java - android获取OnTouchEvent即使应用程序不活动，java空指针

Question

我尝试制作一个应用程序，即使它在后台运行，也可以监听触摸事件，在这里我在论坛中找到了解决方案，但我无法运行

How can a service listen for touch gestures/events?

如果我理解正确的话，执行此操作的方法是使用正确的 windowmanager 参数设置一个新 View ，这是我的代码!

主要 Activity :

public class MainActivity extends Activity {


    View mView;
    HUD mHud; 
    HUDView mHUDView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mHud = new HUD();
        mHUDView = new HUDView(this);

    }


    @Override
    public boolean onTouchEvent(MotionEvent e) {
        mHud.onCreate(this);
        return true;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

目前，为了测试，我只想通过第一次触摸来更改 View ，

public class HUD extends Service  {

    HUDView mView;

    public void onCreate(Context mContext) {
        super.onCreate();

        mView = new HUDView(this);
                WindowManager.LayoutParams params = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.TYPE_SYSTEM_ALERT,
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE|WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL|WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH,
                PixelFormat.TRANSLUCENT);

        params.gravity = Gravity.RIGHT | Gravity.TOP;
        params.setTitle("Load Average");
        WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
        wm.addView(mView, params);
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }

}



class HUDView extends ViewGroup {

    public HUDView(Context context) {
        super(context);  
    }


    @Override
    protected void onLayout(boolean arg0, int arg1, int arg2, int arg3, int arg4) {
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d("ontouch", "clicked in the HUD View");
        //Toast.makeText(getContext(),"onTouchEvent", Toast.LENGTH_LONG).show();
        return true;
    }
}

我对java不太有信心，我得到的错误是javaNullPointerException错误。我知道发生这种情况是因为一个对象变成了空，但是我如何将对象传递给类和子类。

这里是日志:

11-18 11:56:03.791: E/AndroidRuntime(5095): FATAL EXCEPTION: main
11-18 11:56:03.791: E/AndroidRuntime(5095): java.lang.NullPointerException
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.content.ContextWrapper.getResources(ContextWrapper.java:80)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.view.View.<init>(View.java:1810)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.view.ViewGroup.<init>(ViewGroup.java:288)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at com.holzi.runinbackground.HUDView.<init>(HUD.java:47)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at com.holzi.runinbackground.HUD.onCreate(HUD.java:22)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at com.holzi.runinbackground.MainActivity.onTouchEvent(MainActivity.java:32)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.app.Activity.dispatchTouchEvent(Activity.java:2096)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1685)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1802)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.os.Looper.loop(Looper.java:143)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at android.app.ActivityThread.main(ActivityThread.java:4914)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at java.lang.reflect.Method.invokeNative(Native Method)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at java.lang.reflect.Method.invoke(Method.java:521)
11-18 11:56:03.791: E/AndroidRuntime(5095):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)

谢谢!

Answer 1

您将 this 作为上下文传递给 HUDView，this 是您的 Service，它不在附加之前有一个基本上下文，因此如果调用 getResources() ，则会抛出异常。

您需要等到attachBaseContext被调用，或者使用另一个Context来实例化HUDView而不是服务，也许是Application上下文。