我正在开发一个 Android 应用程序，我正在使用拖放 View 。

我在我的 View (屏幕截图中的圆圈)上实现了 onLongClick(实际上使用具有 1.5 秒长点击阈值的 onTouch)。当检测到长按时，我会显示两个拖放区域(单独附加 onDragListener 的 ImageView ，屏幕截图中的绿色框)。

当我的 View 被拖放到任一拖放区域(调用 ACTION_DROP)时，我的代码工作正常，但问题是，我还需要能够判断我的圆圈何时被拖放到拖放区域之外，所以我可以重置状态。在这种情况下，我没有从两个放置区域中的任何一个触发任何回调。我认为我也没有从使用 startDrag 方法的 View 中看到任何可调用的方法。

在将我的 View 放到任何放置区域之外后，我从 logcat 得到的唯一信息是:

I/ViewRootImpl﹕ Reporting drop result: false

有什么方法可以从我的代码中检测到“drop result: false”？帮助将不胜感激!

截图链接如下:

------------ 11 月 21 日更新------------

当我第一次发布这个问题时，我还在努力掌握高级概念，但现在我意识到我应该包含更多细节。

以下是目前在我的应用中使用的一些代码 fragment 。顺便说一下，我在服务中使用那些 View ——圆( anchor )和绿色框(dropRegions)——而不是 Activity ，所以我使用 WindowManager 来添加 View 。

我仍然有同样的问题，我没有得到的主要内容是，ACTION_DRAG_ENTERED 和 ACTION_DRAG_EXITED 从未被调用过。到目前为止，只有 ACTION_DROP 对我有用。我还缺少什么吗？

下面是代码的相关部分。

长按圆圈时调用(根据sandrstar的回应修改了一下):

private void anchorOnLongClick(View view) {
    Log.d("####", "LONG CLICK");
    showAnchorDropRegion();

    ClipData.Item item = new ClipData.Item((String) view.getTag());
    ClipData data = new ClipData((String) view.getTag(),
            new String[]{ClipDescription.MIMETYPE_TEXT_PLAIN}, item);

    View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
    view.startDrag(data, shadowBuilder, null, 0);
    setupAnchorDropRegion();
    showAnchorDropRegion();
}

将拖动监听器附加到绿色框:

/* set up the region where anchor can be drag-and-dropped */
private void setupAnchorDropRegion() {
    ivDropRight = new ImageView(this);
    ivDropRight.setImageDrawable(getResources().getDrawable(R.drawable.dropregion_normal));
    ivDropRight.setOnDragListener(new View.OnDragListener() {
        @Override
        public boolean onDrag(View v, DragEvent event) {
            Log.d("####", "onDrag");
            switch (event.getAction()) {

                case DragEvent.ACTION_DRAG_STARTED:
                    // do nothing
                    return true;

                case DragEvent.ACTION_DRAG_ENTERED:
                    Log.d("####", "DRAG_ENTERED");
                    break;

                case DragEvent.ACTION_DRAG_EXITED:
                    Log.d("####", "DRAG_EXITED");
                    break;

                case DragEvent.ACTION_DROP:
                    Log.d("####", "DROP ON: " + event.getX() + ", " + event.getY());
                    hideDropRegion();
                    // initialize anchor locations to the right
                    break;

                case DragEvent.ACTION_DRAG_ENDED:
                    Log.d("####", "DRAG ENDED");
                    break;

                default:
                    break;
            }
            return true;
        }
    });

// repeat for ivDropLeft

显示绿色框(放置区域):

/* display anchor drop region left and right */
private void showAnchorDropRegion() {
    WindowManager.LayoutParams dropRegionParmas = new WindowManager.LayoutParams(
            app.dropRegionSize, app.dropRegionSize, 0, 0,
            WindowManager.LayoutParams.TYPE_PHONE,
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
            PixelFormat.TRANSLUCENT);
    dropRegionParmas.gravity = Gravity.BOTTOM | Gravity.LEFT;
    mWindowManager.addView(ivDropLeft, dropRegionParmas);

    dropRegionParmas.gravity = Gravity.BOTTOM | Gravity.RIGHT;
    mWindowManager.addView(ivDropRight, dropRegionParmas);
}

最佳答案

主要思想来自 DragEvent.getResult() 的文档:

Returns an indication of the result of the drag and drop operation. This method only returns valid data if the action type is ACTION_DRAG_ENDED. The return value depends on what happens after the user releases the drag shadow.

因此，在 drop 之后，您可以通过 getResult() 获取结果:如果它返回 true 则它已在某个接受 drop 的 View 中被丢弃。请注意，接受 drop 的 View 返回 true 到 ACTION_DROP:

The View should return true from its onDragEvent(DragEvent) handler or OnDragListener.onDrag() listener if it accepted the drop, and false if it ignored the drop.

下面是一些小例子，类似于显示该方法的布局:

public class MainActivity extends Activity {
    private static final String TAG = "MainActivity";

    private View mCircleView = null;
    private Boolean mDroppedIn = null;

    private View.OnDragListener mLeftDragListener = new View.OnDragListener() {
        private boolean mInView = false;

        @Override
        public boolean onDrag(final View v, final DragEvent event) {
            final int action = event.getAction();

            switch (action) {
                case DragEvent.ACTION_DRAG_STARTED:
                    mDroppedIn = null;
                    mCircleView.setVisibility(View.INVISIBLE);
                    v.setBackgroundResource(android.R.color.holo_green_dark);
                    break;

                case DragEvent.ACTION_DRAG_ENTERED:
                    mInView = true;
                    v.setBackgroundResource(android.R.color.holo_green_light);
                    break;

                case DragEvent.ACTION_DRAG_EXITED:
                    mInView = false;
                    v.setBackgroundResource(android.R.color.holo_green_dark);
                    break;

                case DragEvent.ACTION_DRAG_ENDED:
                    mCircleView.post(new Runnable() {
                        @Override
                        public void run() {
                            if (mCircleView.getVisibility() != View.VISIBLE) {
                                mCircleView.setVisibility(View.VISIBLE);
                            }
                        }
                    });
                    reportResult(R.id.leftView, event.getResult());
                    break;

                case DragEvent.ACTION_DROP:
                    return mInView;
            }

            return true;
        }
    };

    private View.OnDragListener mRightDragListener = new View.OnDragListener() {
        private boolean mInView = false;

        @Override
        public boolean onDrag(final View v, final DragEvent event) {
            final int action = event.getAction();

            switch (action) {
                case DragEvent.ACTION_DRAG_STARTED:
                    mDroppedIn = null;
                    mCircleView.setVisibility(View.INVISIBLE);
                    v.setBackgroundResource(android.R.color.holo_green_dark);
                    break;

                case DragEvent.ACTION_DRAG_ENTERED:
                    mInView = true;
                    v.setBackgroundResource(android.R.color.holo_green_light);
                    break;

                case DragEvent.ACTION_DRAG_EXITED:
                    mInView = false;
                    v.setBackgroundResource(android.R.color.holo_green_dark);
                    break;

                case DragEvent.ACTION_DRAG_ENDED:
                    mCircleView.post(new Runnable() {
                        @Override
                        public void run() {
                            if (mCircleView.getVisibility() != View.VISIBLE) {
                                mCircleView.setVisibility(View.VISIBLE);
                            }
                        }
                    });
                    reportResult(R.id.rightView, event.getResult());
                    break;

                case DragEvent.ACTION_DROP:
                    return mInView;
            }

            return true;
        }
    };

    private void reportResult(final int viewId, final boolean result) {
        if (mDroppedIn == null) {
            mDroppedIn = result;
            Toast.makeText(this, "Dropped in: " + result, Toast.LENGTH_SHORT).show();
        }
    }

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

        mCircleView = findViewById(R.id.circleView);

        mCircleView.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(final View v) {
                final ClipData.Item item = new ClipData.Item((String)v.getTag());
                final ClipData dragData = new ClipData((String)v.getTag(),
                        new String[] {ClipDescription.MIMETYPE_TEXT_PLAIN}, item);

                mCircleView.startDrag(dragData, new CircleShadowBuilder(v), null, 0);
                findViewById(R.id.leftView).setOnDragListener(mLeftDragListener);
                findViewById(R.id.rightView).setOnDragListener(mRightDragListener);
                return true;
            }
        });
    }

    private class CircleShadowBuilder extends View.DragShadowBuilder {

        private final Drawable mShadow;

        CircleShadowBuilder(final View v) {
            super(v);
            mShadow = v.getResources().getDrawable(R.drawable.circle);
        }

        @Override
        public void onProvideShadowMetrics(final Point shadowSize, final Point shadowTouchPoint) {
            int width = getView().getWidth();
            int height = getView().getHeight();

            mShadow.setBounds(0, 0, width, height);
            shadowSize.set(width, height);
            shadowTouchPoint.set(width, height);
        }

        @Override
        public void onDrawShadow(final Canvas canvas) {
            mShadow.draw(canvas);
        }
    }
}

关于android - 如何检测 Android 中可拖动 View 外的拖放，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26911748/