我正在尝试将fling手势添加到imageview。我正在使用此代码
public class MyActivity extends Activity {
private void onCreate() {
final GestureDetector gdt = new GestureDetector(new GestureListener());
final ImageView imageView = (ImageView) findViewById(R.id.image_view);
imageView.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(final View view, final MotionEvent event) {
gdt.onTouchEvent(event);
return true;
}
});
}
private static final int SWIPE_MIN_DISTANCE = 120;
private static final int SWIPE_THRESHOLD_VELOCITY = 200;
private class GestureListener extends SimpleOnGestureListener {
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
return false; // Right to left
} else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
return false; // Left to right
}
if(e1.getY() - e2.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {
return false; // Bottom to top
} else if (e2.getY() - e1.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {
return false; // Top to bottom
}
return false;
}
}
}
但它不起作用。日志表示nullpointerexception,它引用此行imageView.setOnTouchListener(new OnTouchListener() {
我的错误在哪里?我错过了什么吗?
答案 0 :(得分:1)
您的imageView返回null,因为在实际获取imageview之前U没有setContentView()
在获取imageview之前,你的onCreate中的 setContentView(R.layout.yourlayout)