Question

我一直在尝试在Android中实现一个非常简单的拖放操作，其中拖动的项目与放置它的项目交换位置。

我已经成功实现了onLongClick和onDrag监听器。当我拖放一个项目时，它会替换掉它所放置的项目，但我无法弄清楚如何使被替换的项目取代被拖动的项目。

我花了一些时间寻找答案，但大多数答案只是链接了涉及许多代码的拖放的复杂实现，我无法理解它们以将它们应用到我的代码中。

我最初假设我没有使用

获得ImageView的真实副本

ImageView temp = (ImageView) event.getLocalState();

所以我试过

ImageView dragged = (ImageView) findViewById(temp.getId());

但这并没有什么不同。

我几乎可以肯定问题出现在'OnDragListener'中，在'case DragEvent.ACTION_DROP：'中。这是我的代码（来自Main.java）：

public class Main extends ActionBarActivity {

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

        findViewById(R.id.ball1).setOnLongClickListener(listenClick);
        findViewById(R.id.ball1).setOnDragListener(listenDrag);
        findViewById(R.id.target1).setOnLongClickListener(listenClick);
        findViewById(R.id.target1).setOnDragListener(listenDrag);
        findViewById(R.id.target2).setOnDragListener(listenDrag);
        findViewById(R.id.target2).setOnLongClickListener(listenClick);
        findViewById(R.id.target3).setOnDragListener(listenDrag);
        findViewById(R.id.target3).setOnLongClickListener(listenClick);



View.OnLongClickListener listenClick = new View.OnLongClickListener()
    {
        @Override
        public boolean onLongClick(View v)
        {

            ClipData data = ClipData.newPlainText("","");
            DragShadow dragShadow = new DragShadow(v);

            v.startDrag(data, dragShadow, v, 0);

            return false;
        }
    };

    private class DragShadow extends View.DragShadowBuilder
    {
        ColorDrawable greyBox;

        public DragShadow(View view)
        {
            super(view);
            greyBox = new ColorDrawable(Color.LTGRAY);
        }

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

        @Override
        public void onProvideShadowMetrics(Point shadowSize,
                                           Point shadowTouchPoint)
        {
            View v = getView();

            int height = (int) v.getHeight();
            int width = (int) v.getWidth();

            greyBox.setBounds(0, 0, width, height);

            shadowSize.set(width, height);

            shadowTouchPoint.set((int)width/2, (int)height/2);
        }
    }



View.OnDragListener listenDrag = new View.OnDragListener() {

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

            switch (dragEvent)
            {
                case DragEvent.ACTION_DRAG_ENTERED:
                    Log.i("Drag Event", "Entered");
                    break;

                case DragEvent.ACTION_DRAG_EXITED:
                    Log.i("Drag Event", "Exited");
                    break;

                case DragEvent.ACTION_DROP:
                    ImageView target = (ImageView) v;

                    ImageView temp = (ImageView) event.getLocalState();
                    ImageView dragged = (ImageView) findViewById(temp.getId());


                    target.setId(dragged.getId());
                    target.setImageDrawable(dragged.getDrawable());

                    dragged.setId(temp.getId());
                    dragged.setImageDrawable(temp.getDrawable());

                    break;

            }

            return true;
        }
    };

如果有人能告诉我为什么setImageDrawable在目标上工作，而不是在拖动，我会非常感激。

Answer 1

进入计算机科学的一大乐趣就是学习谦虚。至少有90％的时间，这个任务的答案是：“为什么这不起作用？”是你告诉电脑做错了。

在“case DragEvent.ACTION_DROP：”中我得到了对两个视图的引用。我出于某种原因没有意识到的是，当我做的时候

target.setImageDrawable(dragged.getDrawable());

我也在改变temp的drawable，因为temp指的是实际的视图。因为那时我做了

dragged.setImageDrawable(temp.getDrawable());

我实际上只是将拖动的drawable设置为原来的状态。这是更正后的代码。

            case DragEvent.ACTION_DROP:
                ImageView target = (ImageView) v;

                ImageView dragged = (ImageView) event.getLocalState();

                Drawable target_draw = target.getDrawable();
                Drawable dragged_draw = dragged.getDrawable();

                dragged.setImageDrawable(target_draw);
                target.setImageDrawable(dragged_draw);

                break;

Answer 2

我更新了答案，可以实际交换视图而不是交换图像；

@RequiresApi(Build.VERSION_CODES.JELLY_BEAN)
private fun initView(view: View) {
    view.setOnDragListener(View.OnDragListener { target, event ->
        when (event.action) {
            DragEvent.ACTION_DRAG_STARTED -> return@OnDragListener true

            DragEvent.ACTION_DRAG_ENTERED -> {
                target.setBackgroundColor(ContextCompat.getColor(this, R.color.colorAccent))
                return@OnDragListener true
            }

            DragEvent.ACTION_DRAG_LOCATION -> return@OnDragListener true

            DragEvent.ACTION_DRAG_EXITED -> {
                target.setBackgroundColor(ContextCompat.getColor(this, R.color.colorPrimary))
                return@OnDragListener true
            }

            DragEvent.ACTION_DROP -> {
                target.setBackgroundColor(ContextCompat.getColor(this, R.color.colorPrimary))

                val dragged = event.localState as ImageView
                val targetView = target as ImageView

                //Swap Image
               // val target_draw = targetView!!.drawable
               // val dragged_draw = dragged!!.drawable

               // dragged.setImageDrawable(target_draw)
               // targetView.setImageDrawable(dragged_draw)

                val oldOwner  = dragged.parent as ViewGroup
                val newOwner  = target.parent as ViewGroup

                val draggedPosition = oldOwner.indexOfChild(dragged)
                val targetPosition = oldOwner.indexOfChild(dragged)


                oldOwner.removeView(dragged)
                newOwner.addView(dragged,targetPosition)

                newOwner.removeView(target)
                oldOwner.addView(target,draggedPosition)

                return@OnDragListener true
            }

            DragEvent.ACTION_DRAG_ENDED -> return@OnDragListener true

            else -> {
            }
        }
        false
    })


    view.setOnLongClickListener { v ->

        val dummyData = ClipData.newPlainText("dummyData", "") // don't forget to pass empty String
        val shadowBuilder = View.DragShadowBuilder(v)
        v.startDrag(dummyData, shadowBuilder, v, 0)

        //val data = ClipData.newPlainText("value", "1")
        // view.startDrag(data, View.DragShadowBuilder(v), null, 0)
        true
    }
}

如何在Android中使用拖放交换两个图片视图？

2 个答案: