Как создать прямоугольник с изменяемым размером с событиями касания пользователя на Android?

Чтобы реализовать собственное представление, вы получаете класс от представления :) Переопределите onDraw() для внешнего вида, переопределите onTouchEvent() для обработки ввода. Обратите внимание, что в Android вы не можете рисовать в представлении за пределами onDraw(); если вы хотите обновить представление, вызовите invalidate().

Вы можете реализовать перетаскиваемые углы как отдельные представления. Для внешнего вида просто используйте готовые изображения (не стесняйтесь получать от ImageView). Перетаскивание реализовано как перемещение вашего представления в ответ на события касания. RelativeLayout — ваш друг для произвольного позиционирования.

Вы можете добавить в макет самодельные виды; просто перейдите к редактированию XML и введите элемент <com.mypackage.MyViewClass>.

Ответ Чинтана Ратода был отличным решением, но что-то не так, когда он рисует прямоугольник. Я просто редактирую некоторые строки кода, чтобы он правильно работал с событием касания пользователя. Теперь вы можете добавить этот вид в свой макет, а затем коснуться, чтобы нарисовать.

import java.util.ArrayList;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import com.ihnel.englishpronounciation.R;

public class DrawView extends View {

    Point[] points = new Point[4];

    /**
     * point1 and point 3 are of same group and same as point 2 and point4
     */
    int groupId = -1;
    private ArrayList<ColorBall> colorballs = new ArrayList<ColorBall>();
    // array that holds the balls
    private int balID = 0;
    // variable to know what ball is being dragged
    Paint paint;
    Canvas canvas;

    public DrawView(Context context) {
        super(context);
        paint = new Paint();
        setFocusable(true); // necessary for getting the touch events
        canvas = new Canvas();
    }

    public DrawView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public DrawView(Context context, AttributeSet attrs) {
        super(context, attrs);
        paint = new Paint();
        setFocusable(true); // necessary for getting the touch events
        canvas = new Canvas();
    }

    // the method that draws the balls
    @Override
    protected void onDraw(Canvas canvas) {
        if(points[3]==null) //point4 null when user did not touch and move on screen.
            return;
        int left, top, right, bottom;
        left = points[0].x;
        top = points[0].y;
        right = points[0].x;
        bottom = points[0].y;
        for (int i = 1; i < points.length; i++) {
            left = left > points[i].x ? points[i].x:left;
            top = top > points[i].y ? points[i].y:top;
            right = right < points[i].x ? points[i].x:right;
            bottom = bottom < points[i].y ? points[i].y:bottom;
        }
        paint.setAntiAlias(true);
        paint.setDither(true);
        paint.setStrokeJoin(Paint.Join.ROUND);
        paint.setStrokeWidth(5);

        //draw stroke
        paint.setStyle(Paint.Style.STROKE);
        paint.setColor(Color.parseColor("#AADB1255"));
        paint.setStrokeWidth(2);
        canvas.drawRect(
                    left + colorballs.get(0).getWidthOfBall() / 2,
                    top + colorballs.get(0).getWidthOfBall() / 2, 
                    right + colorballs.get(2).getWidthOfBall() / 2, 
                    bottom + colorballs.get(2).getWidthOfBall() / 2, paint);
        //fill the rectangle
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(Color.parseColor("#55DB1255"));
        paint.setStrokeWidth(0);
        canvas.drawRect(
                left + colorballs.get(0).getWidthOfBall() / 2,
                top + colorballs.get(0).getWidthOfBall() / 2, 
                right + colorballs.get(2).getWidthOfBall() / 2, 
                bottom + colorballs.get(2).getWidthOfBall() / 2, paint);

        //draw the corners
        BitmapDrawable bitmap = new BitmapDrawable();
        // draw the balls on the canvas
        paint.setColor(Color.BLUE);
        paint.setTextSize(18);
        paint.setStrokeWidth(0);
        for (int i =0; i < colorballs.size(); i ++) {
            ColorBall ball = colorballs.get(i);
            canvas.drawBitmap(ball.getBitmap(), ball.getX(), ball.getY(),
                    paint);

            canvas.drawText("" + (i+1), ball.getX(), ball.getY(), paint);
        }
    }

    // events when touching the screen
    public boolean onTouchEvent(MotionEvent event) {
        int eventaction = event.getAction();

        int X = (int) event.getX();
        int Y = (int) event.getY();

        switch (eventaction) {

        case MotionEvent.ACTION_DOWN: // touch down so check if the finger is on
                                        // a ball
            if (points[0] == null) {
                //initialize rectangle.
                points[0] = new Point();
                points[0].x = X;
                points[0].y = Y;

                points[1] = new Point();
                points[1].x = X;
                points[1].y = Y + 30;

                points[2] = new Point();
                points[2].x = X + 30;
                points[2].y = Y + 30;

                points[3] = new Point();
                points[3].x = X +30;
                points[3].y = Y;

                balID = 2;
                groupId = 1;
                 // declare each ball with the ColorBall class
                for (Point pt : points) {
                     colorballs.add(new ColorBall(getContext(), R.drawable.ic_circle, pt));
                }
            } else {
                //resize rectangle
                balID = -1;
                groupId = -1;
                for (int i = colorballs.size()-1; i>=0; i--) {
                    ColorBall ball = colorballs.get(i);
                    // check if inside the bounds of the ball (circle)
                    // get the center for the ball
                    int centerX = ball.getX() + ball.getWidthOfBall();
                    int centerY = ball.getY() + ball.getHeightOfBall();
                    paint.setColor(Color.CYAN);
                    // calculate the radius from the touch to the center of the
                    // ball
                    double radCircle = Math
                            .sqrt((double) (((centerX - X) * (centerX - X)) + (centerY - Y)
                                    * (centerY - Y)));

                    if (radCircle < ball.getWidthOfBall()) {

                        balID = ball.getID();
                        if (balID == 1 || balID == 3) {
                            groupId = 2;
                        } else {
                            groupId = 1;
                        }
                        invalidate();
                        break;
                    }
                    invalidate();
                }
            }
            break;

        case MotionEvent.ACTION_MOVE: // touch drag with the ball


            if (balID > -1) {
                // move the balls the same as the finger
                colorballs.get(balID).setX(X);
                colorballs.get(balID).setY(Y);

                paint.setColor(Color.CYAN);
                if (groupId == 1) {
                    colorballs.get(1).setX(colorballs.get(0).getX());
                    colorballs.get(1).setY(colorballs.get(2).getY());
                    colorballs.get(3).setX(colorballs.get(2).getX());
                    colorballs.get(3).setY(colorballs.get(0).getY());
                } else {
                    colorballs.get(0).setX(colorballs.get(1).getX());
                    colorballs.get(0).setY(colorballs.get(3).getY());
                    colorballs.get(2).setX(colorballs.get(3).getX());
                    colorballs.get(2).setY(colorballs.get(1).getY());
                }

                invalidate();
            }

            break;

        case MotionEvent.ACTION_UP:
            // touch drop - just do things here after dropping

            break;
        }
        // redraw the canvas
        invalidate();
        return true;

    }


    public static class ColorBall {

        Bitmap bitmap;
        Context mContext;
        Point point;
        int id;
        static int count = 0;

        public ColorBall(Context context, int resourceId, Point point) {
            this.id = count++;
            bitmap = BitmapFactory.decodeResource(context.getResources(),
                    resourceId);
            mContext = context;
            this.point = point;
        }

        public int getWidthOfBall() {
            return bitmap.getWidth();
        }

        public int getHeightOfBall() {
            return bitmap.getHeight();
        }

        public Bitmap getBitmap() {
            return bitmap;
        }

        public int getX() {
            return point.x;
        }

        public int getY() {
            return point.y;
        }

        public int getID() {
            return id;
        }

        public void setX(int x) {
            point.x = x;
        }

        public void setY(int y) {
            point.y = y;
        }
    }
}

Следующий код предназначен для рисования прямоугольника на сенсорной базе.

import java.util.ArrayList;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import com.common.Utils;
import com.example.rectangleoverlay.R;

public class DrawView extends View {

    Point point1, point3;
    Point point2, point4;

    /**
     * point1 and point 3 are of same group and same as point 2 and point4
     */
    int groupId = -1;
    private ArrayList<ColorBall> colorballs = new ArrayList<ColorBall>();
    // array that holds the balls
    private int balID = 0;
    // variable to know what ball is being dragged
    Paint paint;
    Canvas canvas;

    public DrawView(Context context) {
        super(context);
        paint = new Paint();
        setFocusable(true); // necessary for getting the touch events
        canvas = new Canvas();
        // setting the start point for the balls
        point1 = new Point();
        point1.x = 50;
        point1.y = 20;

        point2 = new Point();
        point2.x = 150;
        point2.y = 20;

        point3 = new Point();
        point3.x = 150;
        point3.y = 120;

        point4 = new Point();
        point4.x = 50;
        point4.y = 120;

        // declare each ball with the ColorBall class
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point1));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point2));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point3));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point4));

    }

    public DrawView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public DrawView(Context context, AttributeSet attrs) {
        super(context, attrs);
        paint = new Paint();
        setFocusable(true); // necessary for getting the touch events
        canvas = new Canvas();
        // setting the start point for the balls
        point1 = new Point();
        point1.x = 50;
        point1.y = 20;

        point2 = new Point();
        point2.x = 150;
        point2.y = 20;

        point3 = new Point();
        point3.x = 150;
        point3.y = 120;

        point4 = new Point();
        point4.x = 50;
        point4.y = 120;

        // declare each ball with the ColorBall class
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point1));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point2));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point3));
        colorballs.add(new ColorBall(context, R.drawable.gray_circle, point4));

    }

    // the method that draws the balls
    @Override
    protected void onDraw(Canvas canvas) {
        // canvas.drawColor(0xFFCCCCCC); //if you want another background color

        paint.setAntiAlias(true);
        paint.setDither(true);
        paint.setColor(Color.parseColor("#55000000"));
        paint.setStyle(Paint.Style.FILL);
        paint.setStrokeJoin(Paint.Join.ROUND);
        // mPaint.setStrokeCap(Paint.Cap.ROUND);
        paint.setStrokeWidth(5);

        canvas.drawPaint(paint);
        paint.setColor(Color.parseColor("#55FFFFFF"));

        if (groupId == 1) {
            canvas.drawRect(point1.x + colorballs.get(0).getWidthOfBall() / 2,
                    point3.y + colorballs.get(2).getWidthOfBall() / 2, point3.x
                            + colorballs.get(2).getWidthOfBall() / 2, point1.y
                            + colorballs.get(0).getWidthOfBall() / 2, paint);
        } else {
            canvas.drawRect(point2.x + colorballs.get(1).getWidthOfBall() / 2,
                    point4.y + colorballs.get(3).getWidthOfBall() / 2, point4.x
                            + colorballs.get(3).getWidthOfBall() / 2, point2.y
                            + colorballs.get(1).getWidthOfBall() / 2, paint);
        }
        BitmapDrawable mBitmap;
        mBitmap = new BitmapDrawable();

        // draw the balls on the canvas
        for (ColorBall ball : colorballs) {
            canvas.drawBitmap(ball.getBitmap(), ball.getX(), ball.getY(),
                    new Paint());
        }
    }

    // events when touching the screen
    public boolean onTouchEvent(MotionEvent event) {
        int eventaction = event.getAction();

        int X = (int) event.getX();
        int Y = (int) event.getY();

        switch (eventaction) {

        case MotionEvent.ACTION_DOWN: // touch down so check if the finger is on
                                        // a ball
            balID = -1;
            groupId = -1;
            for (ColorBall ball : colorballs) {
                // check if inside the bounds of the ball (circle)
                // get the center for the ball
                Utils.logd("Id : " + ball.getID());
                Utils.logd("getX : " + ball.getX() + " getY() : " + ball.getY());
                int centerX = ball.getX() + ball.getWidthOfBall();
                int centerY = ball.getY() + ball.getHeightOfBall();
                paint.setColor(Color.CYAN);
                // calculate the radius from the touch to the center of the ball
                double radCircle = Math
                        .sqrt((double) (((centerX - X) * (centerX - X)) + (centerY - Y)
                                * (centerY - Y)));

                Utils.logd("X : " + X + " Y : " + Y + " centerX : " + centerX
                        + " CenterY : " + centerY + " radCircle : " + radCircle);

                if (radCircle < ball.getWidthOfBall()) {

                    balID = ball.getID();
                    Utils.logd("Selected ball : " + balID);
                    if (balID == 1 || balID == 3) {
                        groupId = 2;
                        canvas.drawRect(point1.x, point3.y, point3.x, point1.y,
                                paint);
                    } else {
                        groupId = 1;
                        canvas.drawRect(point2.x, point4.y, point4.x, point2.y,
                                paint);
                    }
                    invalidate();
                    break;
                }
                invalidate();
            }

            break;

        case MotionEvent.ACTION_MOVE: // touch drag with the ball
            // move the balls the same as the finger
            if (balID > -1) {
                Utils.logd("Moving Ball : " + balID);

                colorballs.get(balID).setX(X);
                colorballs.get(balID).setY(Y);

                paint.setColor(Color.CYAN);

                if (groupId == 1) {
                    colorballs.get(1).setX(colorballs.get(0).getX());
                    colorballs.get(1).setY(colorballs.get(2).getY());
                    colorballs.get(3).setX(colorballs.get(2).getX());
                    colorballs.get(3).setY(colorballs.get(0).getY());
                    canvas.drawRect(point1.x, point3.y, point3.x, point1.y,
                            paint);
                } else {
                    colorballs.get(0).setX(colorballs.get(1).getX());
                    colorballs.get(0).setY(colorballs.get(3).getY());
                    colorballs.get(2).setX(colorballs.get(3).getX());
                    colorballs.get(2).setY(colorballs.get(1).getY());
                    canvas.drawRect(point2.x, point4.y, point4.x, point2.y,
                            paint);
                }

                invalidate();
            }

            break;

        case MotionEvent.ACTION_UP:
            // touch drop - just do things here after dropping

            break;
        }
        // redraw the canvas
        invalidate();
        return true;

    }

    public void shade_region_between_points() {
        canvas.drawRect(point1.x, point3.y, point3.x, point1.y, paint);
    }
}

Следующий класс используется для хранения объектов

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Point;

public class ColorBall {

    Bitmap bitmap;
    Context mContext;
    Point point;
    int id;
    static int count = 0;

    public ColorBall(Context context, int resourceId, Point point) {
        this.id = count++;
        bitmap = BitmapFactory.decodeResource(context.getResources(),
                resourceId);
        mContext = context;
        this.point = point;
    }

    public int getWidthOfBall() {
        return bitmap.getWidth();
    }

    public int getHeightOfBall() {
        return bitmap.getHeight();
    }

    public Bitmap getBitmap() {
        return bitmap;
    }

    public int getX() {
        return point.x;
    }

    public int getY() {
        return point.y;
    }

    public int getID() {
        return id;
    }

    public void setX(int x) {
        point.x = x;
    }

    public void setY(int y) {
        point.y = y;
    }
}

Рабочая демонстрация https://www.youtube.com/watch?v=BfYd7Xa-tCc

Я не был доволен ответами с самым высоким рейтингом по нескольким причинам.

1. их было нелегко использовать в качестве представления в xml — атрибуты отсутствуют, поэтому представление не может быть легко переработано.

2. казалось глупым создавать растровые изображения, когда проще добавить рисуемый объект в xml

3. они не учитывают края обзора

4. они не предотвращают инверсию прямоугольника, перетаскивая его слишком далеко влево или вверх

5. они не учитывают смещение от положения касания до центра угловых точек

6. они оба зависят от устаревшего метода растрового изображения.

7. и самое главное, я не мог заставить ни один из них на самом деле работать

Я признаю, что мое решение специализировано для квадратного вида, но его можно довольно легко настроить, чтобы иметь независимые длины сторон X и Y.

поместите это в папку res/values:

custom_attributes.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="IconCropView">
        <attr name="minimumSide" format="dimension"/>
        <attr name="resizeCornerDrawable" format="reference"/>
        <attr name="moveCornerDrawable" format="reference"/>
        <attr name="cornerColor" format="color"/>
        <attr name="edgeColor" format="color" />
        <attr name="outsideCropColor" format="color" />
        <attr name="cornerSize" format="dimension" />
    </declare-styleable>
</resources>

Добавьте это в пакет Java IconCropView.java.

package your_package;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import your_package.R;

public class IconCropView extends View {

//contants strings
private static final String TAG = "IconCropView";

//drawing objects
private Paint paint;

//point objects
private Point[] points;
private Point start;
private Point offset;

//variable ints
private int minimumSideLength;
private int side;
private int halfCorner;
private int cornerColor;
private int edgeColor;
private int outsideColor;
private int corner = 5;

//variable booleans
private boolean initialized = false;

//drawables
private Drawable moveDrawable;
private Drawable resizeDrawable1, resizeDrawable2, resizeDrawable3;

//context
Context context;

public IconCropView(Context context) {
    super(context);
    this.context = context;
    init(null);
}

public IconCropView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    this.context = context;
    init(attrs);
}

public IconCropView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    this.context = context;
    init(attrs);
}

public IconCropView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    this.context = context;
    init(attrs);
}

private void init(@Nullable AttributeSet attrs){

    paint = new Paint();
    start = new Point();
    offset = new Point();

    TypedArray ta = context.getTheme().obtainStyledAttributes(attrs, R.styleable.IconCropView, 0, 0);

    //initial dimensions
    minimumSideLength = ta.getDimensionPixelSize(R.styleable.IconCropView_minimumSide, 20);
    side = minimumSideLength;
    halfCorner = (ta.getDimensionPixelSize(R.styleable.IconCropView_cornerSize, 20))/2;

    //colors
    cornerColor = ta.getColor(R.styleable.IconCropView_cornerColor, Color.BLACK);
    edgeColor = ta.getColor(R.styleable.IconCropView_edgeColor, Color.WHITE);
    outsideColor = ta.getColor(R.styleable.IconCropView_outsideCropColor, Color.parseColor("#00000088"));

    //initialize corners;
    points = new Point[4];

    points[0] = new Point();
    points[1] = new Point();
    points[2] = new Point();
    points[3] = new Point();

    //init corner locations;
    //top left
    points[0].x = 0;
    points[0].y = 0;

    //top right
    points[1].x = minimumSideLength;
    points[1].y = 0;

    //bottom left
    points[2].x = 0;
    points[2].y = minimumSideLength;

    //bottom right
    points[3].x = minimumSideLength;
    points[3].y = minimumSideLength;

    //init drawables
    moveDrawable = ta.getDrawable(R.styleable.IconCropView_moveCornerDrawable);
    resizeDrawable1 = ta.getDrawable(R.styleable.IconCropView_resizeCornerDrawable);
    resizeDrawable2 = ta.getDrawable(R.styleable.IconCropView_resizeCornerDrawable);
    resizeDrawable3 = ta.getDrawable(R.styleable.IconCropView_resizeCornerDrawable);

    //set drawable colors
    moveDrawable.setTint(cornerColor);
    resizeDrawable1.setTint(cornerColor);
    resizeDrawable2.setTint(cornerColor);
    resizeDrawable3.setTint(cornerColor);

    //recycle attributes
    ta.recycle();

    //set initialized to true
    initialized = true;

}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //set paint to draw edge, stroke
    if(initialized) {
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeJoin(Paint.Join.ROUND);
        paint.setColor(edgeColor);
        paint.setStrokeWidth(4);

        //crop rectangle
        canvas.drawRect(points[0].x + halfCorner,points[0].y + halfCorner, points[0].x + halfCorner + side, points[0].y + halfCorner + side, paint);

        //set paint to draw outside color, fill
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(outsideColor);

        //top rectangle
        canvas.drawRect(0, 0, canvas.getWidth(), points[0].y + halfCorner, paint);
        //left rectangle
        canvas.drawRect(0, points[0].y + halfCorner, points[0].x + halfCorner, canvas.getHeight(), paint);
        //right rectangle
        canvas.drawRect(points[0].x + halfCorner + side, points[0].y + halfCorner, canvas.getWidth(), points[0].y + halfCorner + side, paint);
        //bottom rectangle
        canvas.drawRect(points[0].x + halfCorner, points[0].y + halfCorner + side, canvas.getWidth(), canvas.getHeight(), paint);

        //set bounds of drawables
        moveDrawable.setBounds(points[0].x, points[0].y, points[0].x + halfCorner*2, points[0].y + halfCorner*2);
        resizeDrawable1.setBounds(points[1].x, points[1].y, points[1].x + halfCorner*2, points[1].y + halfCorner*2);
        resizeDrawable2.setBounds(points[2].x, points[2].y, points[2].x + halfCorner*2, points[2].y + halfCorner*2);
        resizeDrawable3.setBounds(points[3].x, points[3].y, points[3].x + halfCorner*2, points[3].y+ halfCorner*2);

        //place corner drawables
        moveDrawable.draw(canvas);
        resizeDrawable1.draw(canvas);
        resizeDrawable2.draw(canvas);
        resizeDrawable3.draw(canvas);

    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    //return super.onTouchEvent(event);
    switch(event.getActionMasked()){
        case MotionEvent.ACTION_DOWN:{

            //get the coordinates
            start.x = (int)event.getX();
            start.y = (int)event.getY();

            //get the corner touched if any
            corner = getCorner(start.x, start.y);

            //get the offset of touch(x,y) from corner top-left point
            offset = getOffset(start.x, start.y, corner);

            //account for touch offset in starting point
            start.x = start.x - offset.x;
            start.y = start.y - offset.y;

            break;
        }
        case MotionEvent.ACTION_UP:{

        }
        case MotionEvent.ACTION_MOVE:{
            if(corner == 0) {
                points[0].x = Math.max(points[0].x + (int) Math.min(Math.floor((event.getX() - start.x - offset.x)), Math.floor(getWidth() - points[0].x - 2*halfCorner - side)), 0);
                points[1].x = Math.max(points[1].x + (int) Math.min(Math.floor((event.getX() - start.x - offset.x)), Math.floor(getWidth() - points[1].x - 2*halfCorner)), side);
                points[2].x = Math.max(points[2].x + (int) Math.min(Math.floor((event.getX() - start.x - offset.x)), Math.floor(getWidth() - points[2].x - 2*halfCorner - side)), 0);
                points[3].x = Math.max(points[3].x + (int) Math.min(Math.floor((event.getX() - start.x - offset.x)), Math.floor(getWidth() - points[3].x - 2*halfCorner)), side);

                points[0].y = Math.max(points[0].y + (int) Math.min(Math.floor((event.getY() - start.y - offset.y)), Math.floor(getHeight() - points[0].y - 2*halfCorner - side)), 0);
                points[1].y = Math.max(points[1].y + (int) Math.min(Math.floor((event.getY() - start.y - offset.y)), Math.floor(getHeight() - points[1].y - 2*halfCorner - side)), 0);
                points[2].y = Math.max(points[2].y + (int) Math.min(Math.floor((event.getY() - start.y - offset.y)), Math.floor(getHeight() - points[2].y - 2*halfCorner)), side);
                points[3].y = Math.max(points[3].y + (int) Math.min(Math.floor((event.getY() - start.y - offset.y)), Math.floor(getHeight() - points[3].y - 2*halfCorner)), side);

                start.x = points[0].x;
                start.y = points[0].y;
                invalidate();
            }else if (corner == 1){
                side = Math.min((Math.min((Math.max(minimumSideLength, (int)(side + Math.floor(event.getX()) - start.x - offset.x))), side + (getWidth() - points[1].x - 2* halfCorner ))),side + (getHeight() - points[2].y - 2* halfCorner ));
                points[1].x = points[0].x + side;
                points[3].x = points[0].x + side;
                points[3].y = points[0].y + side;
                points[2].y = points[0].y + side;
                start.x = points[1].x;
                invalidate();
            }else if (corner == 2){
                side =  Math.min((Math.min((Math.max(minimumSideLength, (int)(side + Math.floor(event.getY()) - start.y - offset.y))), side + (getHeight() - points[2].y - 2* halfCorner ))),side + (getWidth() - points[1].x - 2* halfCorner ));
                points[2].y = points[0].y + side;
                points[3].y = points[0].y + side;
                points[3].x = points[0].x + side;
                points[1].x = points[0].x + side;
                start.y = points[2].y;
                invalidate();

            }else if (corner == 3){
                side = Math.min((Math.min((Math.min((Math.max(minimumSideLength, (int)(side + Math.floor(event.getX()) - start.x - offset.x))), side + (getWidth() - points[3].x - 2* halfCorner ))),side + (getHeight() - points[3].y - 2* halfCorner ))), Math.min((Math.min((Math.max(minimumSideLength, (int)(side + Math.floor(event.getY()) - start.y - offset.y))), side + (getHeight() - points[3].y - 2* halfCorner ))),side + (getWidth() - points[3].x - 2* halfCorner )));
                points[1].x = points[0].x + side;
                points[3].x = points[0].x + side;
                points[3].y = points[0].y + side;
                points[2].y = points[0].y + side;
                start.x = points[3].x;

                points[2].y = points[0].y + side;
                points[3].y = points[0].y + side;
                points[3].x = points[0].x + side;
                points[1].x = points[0].x + side;
                start.y = points[3].y;
                invalidate();

            }
            break;
        }
    }
    return true;
}

private int getCorner(float x, float y){
    int corner = 5;
    for (int i = 0; i < points.length; i++){
        float dx = x - points[i].x;
        float dy = y - points[i].y;
        int max = halfCorner * 2;
        if(dx <= max && dx >= 0 && dy <= max && dy >= 0){
            return i;
        }
    }
    return corner;
}

private Point getOffset(int left, int top, int corner){
    Point offset = new Point();
    if(corner == 5){
        offset.x = 0;
        offset.y = 0;
    }else{
        offset.x = left - points[corner].x;
        offset.y = top - points[corner].y;
    }
    return offset;
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
}

В XML-файле вашего макета:

1. Вы должны указать рисуемый угол перемещения

2. Вы должны указать рисование для изменения размера углов

3. размер угла по умолчанию равен 20px

4. Минимальная сторона должна быть не меньше размера угла — значение по умолчанию — 20 пикселей.

5. Вы должны включить пространство имен http://schemas.android.com/apk/res-auto в ваше корневое представление (я использовал псевдоним, xlmn:app=http://schemas.android.com /apk/рес-авто)

пример XML-макета

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="@color/primary"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


<ImageView
    android:id="@+id/crop_image"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginStart="10dp"
    android:layout_marginTop="10dp"
    android:layout_marginEnd="10dp"
    android:layout_marginBottom="10dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.0"
    app:srcCompat="@mipmap/ic_launcher" />

<your_package.IconCropView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/transparent"
    app:minimumSide="60dp"
    app:resizeCornerDrawable="@drawable/adjust_edge_circle"
    app:moveCornerDrawable="@drawable/move_box_circle"
    app:cornerColor="@color/turq"
    app:edgeColor="@color/colorPrimary"
    app:outsideCropColor="@color/transparent_50"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:cornerSize="20dp"/>

Отредактированный ответ Нгуен Минь Биня сработал для меня. Но мне нужно было добавить облегченное исправление, чтобы идентификатор мяча не выходил за пределы досягаемости. Это происходило для меня, если мне приходилось повторно открывать действие, в котором размещено пользовательское представление. Я исправил эти строки:

this.id = количество++;

to:

if (count > 3) count = 0; 
this.id = count++;

Следующий код представляет собой версию C# (в настоящее время я разрабатываю приложение на MonoDroid/Xamarin) запрошенного кода, но с некоторыми улучшениями и возможностью перетаскивания прямоугольника. Еще хочу добавить некоторые функции, отредактирую позже.

namespace ImagePlayground
{
[Activity (Label = "MyView2")]          
public class MyView2 : View
{
    Graphics.Point[] points = new Graphics.Point[4];

    // Array that hold the circle
    private List<ResizeCircle> circles = new List<ResizeCircle>();

    // Variable to keep tracking of which circle is being dragged
    private int circleId = -1;

    // Points are grouped in groups of two so there's always only one fixed point       
    // groupId = 0 > Touch Inside the Rectangle
    // groupId = 1 > Points 0 and 2
    // groupId = 2 > Points 1 and 3
    int groupId = -1;

    // FirstTouch's Coordinate for Tracking on Dragging
    int xFirstTouch = 0;
    int yFirstTouch = 0;

    /** Main Bitmap **/
    private Bitmap mBitmap = null;

    /** Measured Size of the View **/
    private Rect mMeasuredRect;

    /** Paint to Draw Rectangles **/
    private Paint mRectPaint;

    public MyView2(Context ctx) : base (ctx){
        init (ctx);
    }

    public MyView2 (Context ctx, IAttributeSet attrs) : base (ctx, attrs){
        init (ctx);
    }

    public MyView2 (Context ctx, IAttributeSet attrs, int defStyle) : base(ctx,attrs,defStyle){
        init (ctx);
    }

    private void init(Context ctx){
        // For Touch Events
        Focusable = true;
        // Draw the Image on the Background
        mBitmap = BitmapFactory.DecodeResource(ctx.Resources, Resource.Drawable.bg);

        // Sets up the paint for the Drawable Rectangles
        mRectPaint = new Paint ();
        mRectPaint.Color = Android.Graphics.Color.Aqua;
        mRectPaint.StrokeWidth = 4;
        mRectPaint.SetStyle (Paint.Style.Stroke);
    }

    protected override void OnDraw(Canvas canvas){
        // Background Bitmap to Cover all Area
        canvas.DrawBitmap(mBitmap, null, mMeasuredRect, null);

        // Just draw the points only if it has already been initiated
        if (points [3] != null) {               
            int left, top, right, bottom;
            left = points [0].X;
            top = points [0].Y;
            right = points [0].X;
            bottom = points [0].Y;

            // Sets the circles' locations
            for (int i = 1; i < points.Length; i++) {
                left = left > points [i].X ? points [i].X : left;
                top = top > points [i].Y ? points [i].Y : top;
                right = right < points [i].X ? points [i].X : right;
                bottom = bottom < points [i].Y ? points [i].Y : bottom;
            }

            mRectPaint.AntiAlias = true;
            mRectPaint.Dither = true;
            mRectPaint.StrokeJoin = Paint.Join.Round;
            mRectPaint.StrokeWidth = 5;
            mRectPaint.SetStyle (Paint.Style.Stroke);
            mRectPaint.Color = Graphics.Color.ParseColor ("#0079A3");

            canvas.DrawRect (
                left + circles [0].GetCircleWidth () / 2,
                top + circles [0].GetCircleWidth () / 2, 
                right + circles [2].GetCircleWidth () / 2, 
                bottom + circles [2].GetCircleWidth () / 2, mRectPaint);

            // Fill The Rectangle
            mRectPaint.SetStyle (Paint.Style.Fill);
            mRectPaint.Color = Graphics.Color.ParseColor ("#B2D6E3");
            mRectPaint.Alpha = 75;
            mRectPaint.StrokeWidth = 0;

            canvas.DrawRect (
                left + circles [0].GetCircleWidth () / 2,
                top + circles [0].GetCircleWidth () / 2, 
                right + circles [2].GetCircleWidth () / 2, 
                bottom + circles [2].GetCircleWidth () / 2, mRectPaint);

            // DEBUG
            mRectPaint.Color = Graphics.Color.Red;
            mRectPaint.TextSize = 18;
            mRectPaint.StrokeWidth = 0;

            // Draw every circle on the right position
            for (int i = 0; i < circles.Count (); i++) {
                ResizeCircle circle = circles [i];
                float x = circle.GetX ();
                float y = circle.GetY ();
                canvas.DrawBitmap (circle.GetBitmap (), x, y,
                    mRectPaint);

                // DEBUG
  //                    canvas.DrawText ("" + (i + 1), circle.GetX (), circle.GetY (), mRectPaint);
            }
        }
    }

    public override bool OnTouchEvent(MotionEvent e){

        // Get the Coordinates of Touch
        int xTouch = (int) e.GetX ();
        int yTouch = (int) e.GetY ();
        int actionIndex = e.ActionIndex;

        switch (e.ActionMasked) {
        // In case user touch the screen
        case MotionEventActions.Down:

            // If no points were created
            if (points [0] == null) {
                // Offset to create the points
                int offset = 60;
                // Initialize a new Rectangle.
                points [0] = new Graphics.Point ();
                points [0].X = xTouch;
                points [0].Y = yTouch;

                points [1] = new Graphics.Point ();
                points [1].X = xTouch;
                points [1].Y = yTouch + offset;

                points [2] = new Graphics.Point ();
                points [2].X = xTouch + offset;
                points [2].Y = yTouch + offset;

                points [3] = new Graphics.Point ();
                points [3].X = xTouch + offset;
                points [3].Y = yTouch;

                // Add each circle to circles array
                foreach (Graphics.Point pt in points) {
                    circles.Add (new ResizeCircle (Context, Resource.Drawable.circle, pt));
                }
            } else {
                // Register Which Circle (if any) th user has touched
                groupId = getTouchedCircle (xTouch, yTouch);
                xFirstTouch = xTouch;
                yFirstTouch = yTouch;

            }
            break;
        case MotionEventActions.PointerDown:
            break;

        case MotionEventActions.Move:                                               
            if (groupId == 1 || groupId == 2) {

                // Move touched Circle as the finger moves
                circles[circleId].SetX(xTouch);
                circles[circleId].SetY(yTouch);

                // Move the two other circles accordingly
                if (groupId == 1) {
                    circles[1].SetX(circles[0].GetX());
                    circles[1].SetY(circles[2].GetY());
                    circles[3].SetX(circles[2].GetX());
                    circles[3].SetY(circles[0].GetY());
                } else {                        
                    circles[0].SetX(circles[1].GetX());
                    circles[0].SetY(circles[3].GetY());
                    circles[2].SetX(circles[3].GetX());
                    circles[2].SetY(circles[1].GetY());
                }
                Invalidate();
            } else if (groupId == 0){
                // Calculate the delta for the dragging
                int xDelta =  (xTouch-xFirstTouch);
                int yDelta =  (yTouch-yFirstTouch);
                xFirstTouch = xTouch;
                yFirstTouch = yTouch;

                // Move each circle accordingly
                foreach (ResizeCircle circle in circles) {
                    circle.SetX (circle.GetX () + xDelta);
                    circle.SetY (circle.GetY () + yDelta);
                }

                // Redraw the view
                Invalidate ();              
            }
            break;

        case MotionEventActions.Up:
            break;
        default:
            break;          
        }
        Invalidate ();
        return true;
    }


    private int getTouchedCircle(int xTouch, int yTouch){
        int groupId = -1;
        for (int i = 0; i < circles.Count; i++) {
            ResizeCircle circle = circles [i];

            // Check if the touch was inside the bounds of the circle
            int centerX = circle.GetX () + circle.GetCircleWidth ();
            int centerY = circle.GetY () + circle.GetCircleHeight ();

            // Calculate the radius from the touch to the center of the circle
            double radCircle = Math.Sqrt ((double)(((centerX - xTouch) * (centerX - xTouch)) + (centerY - yTouch)
                * (centerY - yTouch)));

            // If the touch was on one of the circles
            if (radCircle < circle.GetCircleWidth ()) {
                circleId = circle.GetID ();
                if (circleId == 1 || circleId == 3) {
                    groupId = 2;
                    break;
                } else {
                    groupId = 1;
                    break;
                }
            } else {
                // User didn't touch any of the circles nor the inside area
                groupId = -1;
            }
        }
        // If the touch wasn't on one of the circles, check if it was inside the rectangle
        if (groupId == -1) {
            List<int> xCoords = new List<int> ();
            List<int> yCoords = new List<int> ();

            // Gather Coordinates from all circles      
            foreach (ResizeCircle circle in circles){
                xCoords.Add (circle.GetX());
                yCoords.Add (circle.GetY());
            }

            // Store the max and min coordinates
            int minX = xCoords.Min ();
            int maxX = xCoords.Max ();
            int minY = yCoords.Min ();
            int maxY = yCoords.Max ();

            // Check if user has touched inside the rectangle
            if ((xTouch > minX && xTouch < maxX) && (yTouch > minY && yTouch < maxY)) {
                // User has touched inside the Rectangle
                groupId = 0;
            }
        }

        return groupId;
    }

    protected override void OnMeasure(int widthMeasureSpec, int heightMeasureSpec){
        base.OnMeasure (widthMeasureSpec, heightMeasureSpec);

        mMeasuredRect = new Rect (0, 0, MeasuredWidth, MeasuredHeight);
    }

    public class ResizeCircle {

        Bitmap bitmap;
        Graphics.Point point;
        int id;
        static int count = 0;

        public ResizeCircle(Context context, int resourceId, Graphics.Point point) {
            this.id = count++;
            bitmap = BitmapFactory.DecodeResource(context.Resources,
                resourceId);
            Log.Debug("BITMAP" , bitmap.Height.ToString());
            this.point = point;
        }

        public int GetCircleWidth() {
            return bitmap.Width;
        }

        public int GetCircleHeight() {
            return bitmap.Height;
        }

        public Bitmap GetBitmap() {
            return bitmap;
        }

        public int GetX() {
            return point.X;
        }

        public int GetY() {
            return point.Y;
        }

        public int GetID() {
            return id;
        }

        public void SetX(int x) {
            point.X = x;
        }

        public void SetY(int y) {
            point.Y = y;
        }
    }
   }
  }