How to create a resizable rectangle with user touch events on Android?

Question

I want to create a rectangular shape that will be resized with the touches of the user. Below image is a good example of what i want to do:

Is there any example like that? What do I need to study to implement this?

Thanks in advance,

Answer 1

Chintan Rathod's answer was great solution but there are something wrong when He draws the rectangle. I just edit some lines of code to make it works correctly with user touch event. Now, you can add this view to your layout then touch to draw.

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;         }     } } 

Answer 2

To implement a custom view, you derive a class from View :) Override onDraw() for looks, override onTouchEvent() for input processing. Note that in Android, you cannot draw on view outside onDraw(); if you want to refresh the view, call invalidate().

You can implement draggable corners as separate views. For looks, just use ready-made images (feel free to derive from ImageView). Dragging is implemented as moving your view in response to touch events. RelativeLayout is your friend for arbitrary view positining.

You can add homemade views to the layout; just go to XML editing and type a <com.mypackage.MyViewClass> element.