Android 调用onTouch时，gestureListener为null

由于某种原因，当用户从左向右乱扔时，我的应用程序第一次崩溃。但如果他们从右到左抛，效果很好。 它只在我构建的gridView上执行此操作。我的布局基本上是

家长：线性布局

子：GridView

我试图为整个屏幕实现gestureListener，但是如果我为gridView所在的linearLayout实现gestureListener，它不会注册。所以我必须分开做。当我这样做时，我在gridView的firstAction gestureListener上得到一个空指针。。这是密码

//set swipe listener for the calendar view
        calendar.setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View arg0, MotionEvent event) {
                // TODO Auto-generated method stub
                return gestures.onTouchEvent(event);
            }
        });

        //set swipe listener for rest of the view
        mainView.setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View arg0, MotionEvent event) {
                // TODO Auto-generated method stub
                return gestures.onTouchEvent(event);
            }
        });

            @Override
        public boolean onFling(MotionEvent firstAction, MotionEvent secondAction, float velocityX,
                float velocityY) {
            //change the calendar images based on what the user flings. If they fling in between certain
            //months, change the background.

            Toast.makeText(CalendarDisplay.this, Float.toString(firstAction.getX()) + " : "
                    + Float.toString(secondAction.getX()), Toast.LENGTH_SHORT).show();
            //right to left fling
            if (firstAction.getX() - secondAction.getX() > 120 && Math.abs(velocityX) > 200) {
                mainView.setBackgroundDrawable(getResources().getDrawable(R.drawable.spring_bkgr));
                month -= 1;
                if (month < 0) {
                    month = 11;
                    year -= 1;
                    myCal.set(Calendar.YEAR, year);
                    myCal.set(Calendar.MONTH, month);
                    adapter = new CalendarAdapter(CalendarDisplay.this, year, month, currentDay);
                    calendar.setAdapter(adapter);
                    currentDate.setText(DateFormat.format(dateTemplate, myCal.getTimeInMillis()));
                }
                //sets the new month and resets the adapter
                myCal.set(Calendar.MONTH, month);
                adapter = new CalendarAdapter(CalendarDisplay.this, year, month, currentDay);
                calendar.setAdapter(adapter);
                currentDate.setText(DateFormat.format(dateTemplate, myCal.getTimeInMillis()));

                setBackGrounds();

            }
            //left to right fling
            else if (secondAction.getX() - firstAction.getX() > 120 && Math.abs(velocityX) > 200) {
                mainView.setBackgroundDrawable(getResources().getDrawable(R.drawable.summer_bkgr));
                month += 1;
                if (month > 11) {
                    month = 0;
                    year += 1;
                    myCal.set(Calendar.YEAR, year);
                    myCal.set(Calendar.MONTH, month);
                    adapter = new CalendarAdapter(CalendarDisplay.this, year, month, currentDay);
                    calendar.setAdapter(adapter);
                    currentDate.setText(DateFormat.format(dateTemplate, myCal.getTimeInMillis()));
                }
                //probably inefficient but...yeah it works.
                myCal.set(Calendar.MONTH, month);
                adapter = new CalendarAdapter(CalendarDisplay.this, year, month, currentDay);
                calendar.setAdapter(adapter);
                currentDate.setText(DateFormat.format(dateTemplate, myCal.getTimeInMillis()));

                setBackGrounds();
            }

            return true;
        }

---

试试这个

 private final GestureDetector gestureDetector = new GestureDetector(new GestureListener());

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

        page= (TestLayout) findViewById(R.id.mainpage);
        page.setOnTouchListener(this);

    }   
    @Override
    protected void onPause() {
        super.onPause();
        onStop();
    }
    private final class GestureListener extends SimpleOnGestureListener {

        private static final int SWIPE_THRESHOLD = 100;
        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            boolean result = false;
            try {
                float diffY = e2.getY() - e1.getY();
                float diffX = e2.getX() - e1.getX();
                //if (Math.abs(diffX) > Math.abs(diffY)) {
                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffX > 0) {
                            page.pre();
                        } else {
                           page.next();
                        }
                    }
                //} 

            } catch (Exception exception) {
                exception.printStackTrace();
            }
            return result;
        }

使用您的业务逻辑更改方法

page.pre（）

和

page.post（）

---

希望有帮助。

logcat怎么说？onTouch调用上的null指针，然后在onFling中抛出firstAction或secondAction的第一个实例。我想知道这是否与这样一个事实有关，因为它是一个gridView，所以有几个视图被膨胀，每个视图都有自己的手势听众要求？？？onTouch只调用手势。onTouchEvent（事件）；所以NPE的原因很清楚：手势是无效的，而不是。我已经在mainView上测试了它，它可以工作。两个MotionEvents都不能为null，因为您在Toast中使用了它们，对吗？为什么不在onFling中设置断点并逐步调试此方法？很抱歉，这与我的代码没有太大区别：（.谢谢！

 private final GestureDetector gestureDetector = new GestureDetector(new GestureListener());

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

        page= (TestLayout) findViewById(R.id.mainpage);
        page.setOnTouchListener(this);

    }   
    @Override
    protected void onPause() {
        super.onPause();
        onStop();
    }
    private final class GestureListener extends SimpleOnGestureListener {

        private static final int SWIPE_THRESHOLD = 100;
        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            boolean result = false;
            try {
                float diffY = e2.getY() - e1.getY();
                float diffX = e2.getX() - e1.getX();
                //if (Math.abs(diffX) > Math.abs(diffY)) {
                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffX > 0) {
                            page.pre();
                        } else {
                           page.next();
                        }
                    }
                //} 

            } catch (Exception exception) {
                exception.printStackTrace();
            }
            return result;
        }