拖放-java.lang.ArrayIndexOutOfBoundsException

我对android（和Java）是一个完全的新手，我从一个拖放教程中得到了一些示例代码，供大家玩转并尝试理解。做得相当不错，但这段代码会生成java.lang.ArrayIndexOutOfBoundsException错误，并在应用程序启动时每秒强制关闭一次

我猜这可能是关于应用程序没有清除其资源的简单问题，如果有人知道代码的哪一部分导致了它以及为什么会这样，我们将不胜感激。 在1.5和2.2上都试过

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; 

    }
}

---

感谢你对我的帮助

ArrayIndexOutOfBoundsException

ArrayIndexOutOfBoundsException意味着您试图访问数组中不存在的项。例如，您有一个长度为3的数组

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

数组的索引从0开始，因此要获取第一个colorball，您需要
colorballs[0]
，第二个将是
colorballs[1]
，最后是
colorballs[2]

如果您要求使用
colorbolls[3]
，您应该获得execption，因为索引3超出了正确的范围，即0到2（包括0到2）

我不确定代码中的第112行是哪一行，但请查看该行，看看您是否试图使用不在0和2之间的数字访问阵列。
尝试设置

公共静态
int count=0

看看这是否有帮助。
我似乎发现了问题，尽管我不太清楚为什么会发生

在通过后退按钮退出应用程序后，“count”变量显然没有重置，因此它使数组变得疯狂

现在，我更改了代码，以确保每次调用ColorBall（）时计数不超过3（我当前的对象数）（临时解决方法）：

我认为这应该是问题所在：colorballs[balID-1].setY（Y-25）；这很奇怪。我会在那里添加一些日志语句来了解更多的情况，或者在那里放置一个断点并在调试模式下运行，以便您可以看到哪个球导致它崩溃。嗯，不，count必须设置为1，应用程序才能运行。但尝试更改它，错误仍然存在。
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$DecorView.superDispatchTouchEvent(PhoneWindow.java:1671)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at android.app.Activity.dispatchTouchEvent(Activity.java:2086)
10-13 15:15:15.038: ERROR/AndroidRuntime(492):     at com.android.internal.policy.impl.PhoneWindow$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)

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

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;

}