Question

说明

我创建了View，其中我使用canvas绘制了矩形，并在该视图中实现了On Touch Event。

我希望通过这种方式启动新活动。

问题：

现在的问题是，每当我触摸该矩形时，“强制关闭”错误就会弹出。

这是PickCardView.java

  public class PickCardView extends View
    {   
    private Paint mCanvasPaint;

    private Rect mScreenSize = new Rect();

    private Rect mCardSize = new Rect();
    private int mCardCap;

    private Card MCards;

    public PickCardView(Context context) 
    {
        super(context);

        mCanvasPaint = new Paint();
        mCanvasPaint.setColor(0xFF228B22); // Green background
        mCanvasPaint.setAntiAlias(false);
        mCanvasPaint.setFilterBitmap(false);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) 
    {
        super.onSizeChanged(w, h, oldw, oldh);

        // Store current screen size
        mScreenSize.set(0, 0, w, h);

        // Calculate card and decks sizes and positions
        int cw = w / 11;
        mCardSize.set(0, 0, cw, (int) (cw * 1.5));
        Log.v("card size", mCardSize.toString());

        int freeSize = w - cw * 7; //117
        mCardCap = freeSize / (6 + 4 * 2);//5

        int cy = (int) (mScreenSize.height() * 0.35);

        //MIDDLE CARD HOLDER
        MCards = new Card(Card.CardType.PickDeck, mCardCap * 2 + mCardSize.width()*4 - 15, cy - 20, mCardSize.width()+60, mCardSize.height()+60);
    }

    @Override
    public void onDraw(Canvas canvas) 
    {
        mCanvasPaint.setStyle(Style.FILL);
        canvas.drawRect(mScreenSize, mCanvasPaint);

        MCards.doDraw(canvas);     
    }

    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        int action = event.getAction();

        if (action == MotionEvent.ACTION_DOWN) 
        {
            int x = (int) event.getX();
            int y = (int) event.getY();

            Card card = getCardUnderTouch(x, y);

            if(card != null)
            {
                Intent i = new Intent(null, BuildWord.class);  
                startActivity(i);
            }
        }

        return true;
    }

    private void startActivity(Intent i) 
    {
        //Intent i1 = new Intent(null, BuildWord.class);        
    }

    private Card getCardUnderTouch(int x, int y) 
    {
        Card ret = null;

        if (MCards.isUnderTouch(x, y)) 
        {
            return MCards;
        }

        return ret;
    }
}

当触摸该矩形时，这是logcat中显示的错误：

11-13 21:07:12.037: E/InputEventReceiver(712): Exception dispatching input event.
11-13 21:07:12.037: E/MessageQueue-JNI(712): Exception in MessageQueue callback: handleReceiveCallback
11-13 21:07:12.138: E/MessageQueue-JNI(712): java.lang.NullPointerException
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.content.ComponentName.<init>(ComponentName.java:75)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.content.Intent.<init>(Intent.java:3301)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at apk.gameshufflewords.PickCardView.onTouchEvent(PickCardView.java:79)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.View.dispatchTouchEvent(View.java:7127)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1925)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1379)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.app.Activity.dispatchTouchEvent(Activity.java:2396)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1873)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.View.dispatchPointerEvent(View.java:7307)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3174)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3119)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4155)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4134)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4226)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.os.MessageQueue.nativePollOnce(Native Method)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.os.MessageQueue.next(MessageQueue.java:125)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.os.Looper.loop(Looper.java:124)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at android.app.ActivityThread.main(ActivityThread.java:4745)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at java.lang.reflect.Method.invokeNative(Native Method)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at java.lang.reflect.Method.invoke(Method.java:511)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-13 21:07:12.138: E/MessageQueue-JNI(712):    at dalvik.system.NativeStart.main(Native Method)
11-13 21:07:12.167: D/AndroidRuntime(712): Shutting down VM
11-13 21:07:12.167: W/dalvikvm(712): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
11-13 21:07:12.267: E/AndroidRuntime(712): FATAL EXCEPTION: main
11-13 21:07:12.267: E/AndroidRuntime(712): java.lang.NullPointerException
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.content.ComponentName.<init>(ComponentName.java:75)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.content.Intent.<init>(Intent.java:3301)
11-13 21:07:12.267: E/AndroidRuntime(712):  at apk.gameshufflewords.PickCardView.onTouchEvent(PickCardView.java:79)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.View.dispatchTouchEvent(View.java:7127)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
11-13 21:07:12.267: E/AndroidRuntime(712):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1925)
11-13 21:07:12.267: E/AndroidRuntime(712):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1379)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.app.Activity.dispatchTouchEvent(Activity.java:2396)
11-13 21:07:12.267: E/AndroidRuntime(712):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1873)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.View.dispatchPointerEvent(View.java:7307)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3174)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3119)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4155)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4134)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4226)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.os.MessageQueue.nativePollOnce(Native Method)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.os.MessageQueue.next(MessageQueue.java:125)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.os.Looper.loop(Looper.java:124)
11-13 21:07:12.267: E/AndroidRuntime(712):  at android.app.ActivityThread.main(ActivityThread.java:4745)
11-13 21:07:12.267: E/AndroidRuntime(712):  at java.lang.reflect.Method.invokeNative(Native Method)
11-13 21:07:12.267: E/AndroidRuntime(712):  at java.lang.reflect.Method.invoke(Method.java:511)
11-13 21:07:12.267: E/AndroidRuntime(712):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-13 21:07:12.267: E/AndroidRuntime(712):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-13 21:07:12.267: E/AndroidRuntime(712):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

将onTouchEvent更改为

@Override
public boolean onTouchEvent(MotionEvent event)
{
int action = event.getAction();

if (action == MotionEvent.ACTION_DOWN) 
{
    int x = (int) event.getX();
    int y = (int) event.getY();

    Card card = getCardUnderTouch(x, y);

    if(card != null)
    {
        Context context = getContext();
        Intent i = new Intent(context, BuildWord.class);  
        context.startActivity(i);
    }
}

return true;
}

删除你的startActivity方法

Answer 2

您正在以下行中创建一个带有Intent上下文的新null：

Intent i = new Intent(null, BuildWord.class);

您应该执行以下操作：

Context mContext;
public PickCardView(Context context) 
{
    super(context);
    mContext = context;
    ...
}

然后通过以下方式替换意图行：

Intent i = new Intent(mContext, BuildWord.class);

问候。

在Android中的画布错误中的触摸事件

2 个答案: