Drag and drop - java.lang.ArrayIndexOutOfBoundsException

I'm a complete newbie on android (and Java), and got myself some example code from a Drag and Drop tutorial to play around with and try to understand. Doing fairly well, but this code generates the java.lang.ArrayIndexOutOfBoundsException error and a force close every second time the app starts.

I'm guessing it might be something simple about the app not clearing out its resources, would appreciate if someone knows what part of the code is causing it and why. Tried on both 1.5 and 2.2.

Main.java :

package eas.org;

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 eas.org;

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 eas.org;

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;
        }

    }

}

Crash log :

10-13 15:15:15.038: ERROR/AndroidRuntime(492): FATAL EXCEPTION: main
10-13 15:15:15.038: ERROR/AndroidRuntime(492): java.lang.ArrayIndexOutOfBoundsException
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at eas.org.DrawView.onTouchEvent(DrawView.java:112)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.view.View.dispatchTouchEvent(View.java:3766)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:936)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:936)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:936)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1671)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.po开发者_运维百科licy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.app.Activity.dispatchTouchEvent(Activity.java:2086)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1655)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1785)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.os.Looper.loop(Looper.java:123)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.app.ActivityThread.main(ActivityThread.java:4627)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at java.lang.reflect.Method.invokeNative(Native Method)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at java.lang.reflect.Method.invoke(Method.java:521)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at dalvik.system.NativeStart.main(Native Method)

Thankful for any help I can get with this!

An ArrayIndexOutOfBoundsException means that you are trying to access an item in an array that does not exist. For example, you have an array with length 3.

 private ColorBall[] colorballs = new ColorBall[3];

Arrays are indexed starting at 0, so to get the first colorball you would ask for colorballs[0], the second would be colorballs[1] finally collorbals[2].

If you asked for colorballs[3] you should get the execption, because the index, 3, is out of the proper range, 0 to 2 inclusive.

I'm not sure which line 112 is in your code, but look at that line and see if you are trying to access the array with a number not between 0 and 2.

I seem to have found the problem, although I'm not quite sure why it happens.

The "count" variable was apparently not resetting after exiting the app via the back button, and so it made the array go bananas.

I've now changed the code to make sure that count isn't higher than 3 (my current number of objects) every time ColorBall() is called (temporary ugly workaround):

public ColorBall(Context context, int drawable) {

    BitmapFactory.Options opts = new BitmapFactory.Options();
    opts.inJustDecodeBounds = true;
    img = BitmapFactory.decodeResource(context.getResources(), drawable); 
    if (count > 3) count=1;
    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); 
    if (count > 3) count=1;
    id=count;
    count++;
    coordX= point.x;
    coordY = point.y;

}

Try setting

public static int count = 0

And see if that helps.