How to place drag event on button in Android?

Question

On my view I want to place a hidden button, and above this hidden button I want to place an image. Whenever the user drags on the image the button's drag event should be called. Can any one suggest how to do this? As there is no in-built method for drag events in Android.

Answer 1

use this code for drag

Main.java

package com.drag;
import android.app.Activity;
import android.os.Bundle;

public class Main extends Activity{

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
{
        super.onCreate(savedInstanceState);

        // draw the view
        setContentView(new DrawView(this));


    }

}

DrawView.java

package com.drag;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Point;
import android.view.MotionEvent;
import android.view.View;

public class DrawView extends View
 {

   private ColorBall[] colorballs = new ColorBall[3]; // array that holds the balls

   private int balID = 0; // variable to know what ball is being dragged

    public DrawView(Context context) {
        super(context);
        setFocusable(true); //necessary for getting the touch events

        // setting the start point for the balls
        Point point1 = new Point();
        point1.x = 50;
        point1.y = 20;
        Point point2 = new Point();
        point2.x = 100;
        point2.y = 20;
        Point point3 = new Point();
        point3.x = 150;
        point3.y = 20;


        // declare each ball with the ColorBall class
        colorballs[0] = new ColorBall(context,R.drawable.bol_groen, point1);
        colorballs[1] = new ColorBall(context,R.drawable.bol_rood, point2);
        colorballs[2] = new ColorBall(context,R.drawable.bol_blauw, point3);


    }

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

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

    }

    // 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 = 0;
            for (ColorBall ball : colorballs) {
                // check if inside the bounds of the ball (circle)
                // get the center for the ball
                int centerX = ball.getX() + 25;
                int centerY = ball.getY() + 25;

                // 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 the radius is smaller then 23 (radius of a ball is 22), then it must be on the ball
                if (radCircle < 23){
                    balID = ball.getID();
                    break;
                }

                // check all the bounds of the ball (square)
                //if (X > ball.getX() && X < ball.getX()+50 && Y > ball.getY() && Y < ball.getY()+50){
                //  balID = ball.getID();
                //  break;
                //}
              }

             break; 


        case MotionEvent.ACTION_MOVE:   // touch drag with the ball
            // move the balls the same as the finger
            if (balID > 0) {
                colorballs[balID-1].setX(X-25);
                colorballs[balID-1].setY(Y-25);
            }

            break; 

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

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

    }
}

ColorBall.java

package com.drag;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Point;

public class ColorBall 
 {

 private Bitmap img; // the image of the ball

 private int coordX = 0; // the x coordinate at the canvas

 private int coordY = 0; // the y coordinate at the canvas

 private int id; // gives every ball his own id, for now not necessary

 private static int count = 1;

 private boolean goRight = true;

 private boolean goDown = true;

    public ColorBall(Context context, int drawable) {

        BitmapFactory.Options opts = new BitmapFactory.Options();
        opts.inJustDecodeBounds = true;
        img = BitmapFactory.decodeResource(context.getResources(), drawable); 
        id=count;
        count++;

    }

    public ColorBall(Context context, int drawable, Point point) {

        BitmapFactory.Options opts = new BitmapFactory.Options();
        opts.inJustDecodeBounds = true;
        img = BitmapFactory.decodeResource(context.getResources(), drawable); 
        id=count;
        count++;
        coordX= point.x;
        coordY = point.y;

    }

    public static int getCount() {
        return count;
    }

    void setX(int newValue) {
        coordX = newValue;
    }

    public int getX() {
        return coordX;
    }

    void setY(int newValue) {
        coordY = newValue;
   }

    public int getY() {
        return coordY;
    }

    public int getID() {
        return id;
    }

    public Bitmap getBitmap() {
        return img;
    }

    public void moveBall(int goX, int goY) {
        // check the borders, and set the direction if a border has reached
        if (coordX > 270){
            goRight = false;
        }
        if (coordX < 0){
            goRight = true;
        }
        if (coordY > 400){
            goDown = false;
        }
        if (coordY < 0){
            goDown = true;
        }
        // move the x and y 
        if (goRight){
            coordX += goX;
        }else
        {
            coordX -= goX;
        }
        if (goDown){
            coordY += goY;
        }else
        {
            coordY -= goY;
        }

    }

}