您的快速拖动导致您没有处理的甩动，并且拖放工具没有通过正式结束拖动来通知您它没有继续进行。以下更新后的MainActivity.java有以下变化：
- 删除了很多处理与拖动无关的代码。我这样做只是为了简化此处的发布，没有其他原因。
- 引入
GestureDetectorCompat 以检测何时发生投掷。我对此不做任何事情，只是记录它发生了。您可能需要考虑在代码中使用手势检测器来进行触摸。
- 检查
ACTION_UP 事件以在拖动未完成时重置布局 (isDragging == true)。
当拖拽开始时，flings 似乎有一个混乱的结局。下面的代码可以帮助您解决问题。
MainActivity.java
public class MainActivity extends AppCompatActivity {
ImageView ivGrid1, ivGrid2, ivGrid3, ivGrid4;
private GestureDetectorCompat mDetector;
//Drag and Drop
View dragOriginView;
Drawable whiteDrawable;
Drawable tempDrawableStorage;
boolean isDragging = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDetector = new GestureDetectorCompat(this, new MyGestureListener());
ivGrid1 = findViewById(R.id.grid_1);
ivGrid2 = findViewById(R.id.grid_2);
ivGrid3 = findViewById(R.id.grid_3);
ivGrid4 = findViewById(R.id.grid_4);
setupTouchListeners();
setupDragListeners();
whiteDrawable = new ColorDrawable(ContextCompat.getColor(this, android.R.color.white));
}
private void setupTouchListeners() {
View.OnTouchListener listener = new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getActionMasked();
switch (action) {
case MotionEvent.ACTION_DOWN:
return true;
case MotionEvent.ACTION_MOVE:
boolean beyondLeft = event.getX() <= 0;
boolean beyondRight = event.getX() >= v.getWidth();
boolean beyondTop = event.getY() <= 0;
boolean beyondBottom = event.getY() >= v.getHeight();
if (beyondLeft || beyondRight || beyondTop || beyondBottom) {
startDragAndDrop(v);
return true;
}
isDragging = false;
break;
case MotionEvent.ACTION_UP:
if (isDragging) {
dragOriginView.setBackground(tempDrawableStorage);
tempDrawableStorage = null;
v.setAlpha(1.0f);
isDragging = false;
}
}
return false;
}
};
ivGrid1.setOnTouchListener(listener);
ivGrid2.setOnTouchListener(listener);
ivGrid3.setOnTouchListener(listener);
ivGrid4.setOnTouchListener(listener);
}
private void startDragAndDrop(View view) {
if (isDragging) return;
isDragging = true;
dragOriginView = view;
view.setAlpha(0.5f);
ClipData.Item item = new ClipData.Item((String) view.getTag());
ClipData dragData = new ClipData((String) view.getTag(), new String[]{ClipDescription.MIMETYPE_TEXT_PLAIN},
item);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
view.startDragAndDrop(dragData, new View.DragShadowBuilder(view), null, 0);
} else {
view.startDrag(dragData, new View.DragShadowBuilder(view), null, 0);
}
Log.i("dragEvent", "view.startDragAndDrop has been called");
tempDrawableStorage = view.getBackground();
view.setBackground(whiteDrawable);
}
private void setupDragListeners() {
View.OnDragListener listener = new View.OnDragListener() {
@Override
public boolean onDrag(View v, DragEvent event) {
Log.i("dragEvent", "<<<<<<<<<<<<<<called");
switch (event.getAction()) {
case ACTION_DRAG_STARTED:
Log.i("dragEvent", "ACTION_DRAG_STARTED received");
return event.getClipDescription().hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN);
case ACTION_DRAG_ENTERED:
Log.i("dragEvent", "ACTION_DRAG_ENTERED received");
v.setAlpha(0.5f);
return true;
case ACTION_DRAG_LOCATION:
Log.i("dragEvent", "ACTION_DRAG_LOCATION received");
return true;
case ACTION_DRAG_EXITED:
Log.i("dragEvent", "ACTION_DRAG_EXITED received");
v.setAlpha(1f);
return true;
case ACTION_DROP:
Log.i("dragEvent", "ACTION_DROP received");
v.setAlpha(1f);
swapColor(v);
return true;
case ACTION_DRAG_ENDED:
Log.i("dragEvent", "ACTION_DRAG_ENDED received");
if (!event.getResult() && v == dragOriginView) {
dragOriginView.setBackground(tempDrawableStorage);
tempDrawableStorage = null;
}
v.setAlpha(1f);
isDragging = false;
default:
//Do nothing
}
return false;
}
};
ivGrid1.setOnDragListener(listener);
ivGrid2.setOnDragListener(listener);
ivGrid3.setOnDragListener(listener);
ivGrid4.setOnDragListener(listener);
}
private void swapColor(View dragTarget) {
if (dragOriginView == dragTarget) {
//Restore color
dragOriginView.setBackground(tempDrawableStorage);
tempDrawableStorage = null;
return;
}
Drawable targetBackground = dragTarget.getBackground();
dragOriginView.setBackground(targetBackground);
dragTarget.setBackground(tempDrawableStorage);
tempDrawableStorage = null;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
this.mDetector.onTouchEvent(event);
return super.onTouchEvent(event);
}
class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
private static final String DEBUG_TAG = "Gestures";
@Override
public boolean onDown(MotionEvent event) {
Log.d(DEBUG_TAG, "onDown: " + event.toString());
return true;
}
@Override
public boolean onFling(MotionEvent event1, MotionEvent event2,
float velocityX, float velocityY) {
Log.d(DEBUG_TAG, "onFling: " + ((event1 != null) ? event1.toString() : "" + event2.toString()));
return true;
}
}
}