我正在尝试向 ImageView 添加滑动手势。我正在使用这段代码
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;
}
}
}
但这根本行不通。日志显示 nullpointerexception，它指的是这一行 imageView.setOnTouchListener(new OnTouchListener() {
我的错误在哪里？我错过了什么吗？
最佳答案
您的 imageView 返回 null，因为您在实际获取 imageview 之前没有 setContentView()
setContentView(R.layout.yourlayout) 在获取 ImageView 之前在 onCreate 中
关于java - 向 ImageView 添加滑动手势，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14911302/