Exception dispatching input event，Exception in MessageQueue callback: handleReceiveCallback，空指针

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最新推荐文章于 2021-09-03 15:24:50 发布

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分类专栏：错误累积（错题本）文章标签： SurfaceView SurfaceHolder.Callback

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本文详细解析了一次在自定义SurfaceView中遇到的空指针异常问题，通过错误信息定位到MySurfaceView类的onTouchEvent方法，发现DrawingThread对象未正确初始化。问题在于未在构造方法中调用initParams方法添加SurfaceHolder.Callback监听，导致surfaceCreated方法未被调用。

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一、错误信息

02-12 19:49:22.167 30890-30890/com.luminal.imageview.draw.myapplication E/InputEventReceiver: Exception dispatching input event.
02-12 19:49:22.167 30890-30890/com.luminal.imageview.draw.myapplication E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
02-12 19:49:22.167 30890-30890/com.luminal.imageview.draw.myapplication E/MessageQueue-JNI: java.lang.NullPointerException
at com.luminal.imageview.draw.myapplication.MySurfaceView.onTouchEvent(MySurfaceView.java:83)
at android.view.View.dispatchTouchEvent(View.java:7706)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2216)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2068)
at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1515)
at android.app.Activity.dispatchTouchEvent(Activity.java:2458)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2016)
at android.view.View.dispatchPointerEvent(View.java:7886)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:3978)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3857)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3423)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3473)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3442)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3549)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3450)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3606)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3423)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3473)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3442)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3450)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3423)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5626)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5606)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5577)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5706)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:138)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:5019)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)

二、解决方式

1、根据错误信息，空指针异常，我们知道某个对象为空

2、根据错误第83行，我们知道定位错误出现在哪一行。我们可以输出对象查看

如：我自定义的SurfaceView类MySurfaceView，里面自定义了绘制线程DrawingThread，打印输出后drawingThread对象为null

    //7、添加触摸事件，创建DrawingItem对象
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //监听down事件
        if(event.getAction() == MotionEvent.ACTION_DOWN){

            Log.v("SurfaceView@@@","点击屏幕后："+drawingThread);
            //添加图片对象
            drawingThread.addItem(event.getX(),event.getY());

        }
        return super.onTouchEvent(event);
    }

而DrawingThread对象是在，surfaceCreated方法里面调用的

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        //创建
        //6、通过SurfaceView的生命周期来执行我们的线程，绘制我们的图片
        //此图片为资源文件里面的默认图片
        drawingThread = new DrawingThread(getHolder(),
                BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher));
        drawingThread.start();
    }

那么什么时候调用surfaceCreated方法呢？

1、MySurfaceView类实现接口SurfaceHolder.Callback，重写回调方法surfaceCreated

2、添加对接口SurfaceHolder.Callback的监听

就是在MySurfaceView构造方法里面，没有调用initParams方法，没有实现接口的监听，才会报错。

    public MySurfaceView(Context context) {
        super(context);
        initParams();
    }

    public MySurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initParams();
    }

    //2、监听SurfaceView的生命周期
    private void initParams(){
        getHolder().addCallback(this);
    }