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PORetrieving precise drop position of Android View
 

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  1. PORetrieving precise drop position of Android View
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    <p>The target application allows the user to drag/drop views to move them in a FrameLayout or store them in another LinearLayout.</p> <p>The overall mechanism works but I can't get the precision I need on the position when the view is dropped, it "jumps" a little further. How could I retrieve the position of the drag shadow to put the dropped view exactly where the shadow was, in order to avoid any "jump" artefact?</p> <p>For the sake of the example, the layout is pretty simple, here's an overview with two TextView objects that can be moved around (I removed all the details):</p> <pre class="lang-xml prettyprint-override"><code>&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"&gt; &lt;LinearLayout android:id="@+id/repository"/&gt; &lt;FrameLayout android:id="@+id/frame"&gt; &lt;TextView android:id="@+id/view1"/&gt; &lt;TextView android:id="@+id/view2"/&gt; &lt;/FrameLayout&gt; &lt;/LinearLayout&gt; </code></pre> <p>First, to improve the start position of the drag shadow itself, I'm overriding <code>onProvideShadowMetrics</code>. Thanks to that, the view doesn't jump when the user starts dragging it:</p> <pre class="lang-java prettyprint-override"><code>private class MyDragShadowBuilder extends View.DragShadowBuilder { private float x, y; public MyDragShadowBuilder(View view, float x, float y) { super(view); this.x = x; this.y = y; } @Override public void onProvideShadowMetrics(Point size, Point touchPoint) { super.onProvideShadowMetrics(size, touchPoint); touchPoint.set((int) x, (int) y); } } </code></pre> <p>Then an implementation of the <code>OnTouchListener</code> is used to start the drag operation:</p> <pre class="lang-java prettyprint-override"><code>private class LongClickListener implements View.OnTouchListener { @Override public boolean onTouch(View v, MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_DOWN) { TextView tv = (TextView) v; if (tv != null) { ClipData data = ClipData.newPlainText("", ""); MyDragShadowBuilder shadowBuilder = new MyDragShadowBuilder(v, event.getX(), event.getY()); v.startDrag(data, shadowBuilder, v, 0); v.setVisibility(View.INVISIBLE); return true; } } return false; } } </code></pre> <p>The drop operation is where I would like to retrieve the initial x, y position of the "finger" in the view, to position the view exactly as the shadow.</p> <pre class="lang-java prettyprint-override"><code>private class DragListener implements View.OnDragListener { private final Class&lt;?&gt; FRAMELAYOUT_CLASS = FrameLayout.class; private final Class&lt;?&gt; LINEARLAYOUT_CLASS = LinearLayout.class; private Drawable enterShape = getResources().getDrawable(R.drawable.shape_droptarget); private Drawable normalShape = getResources().getDrawable(R.drawable.shape); @Override public boolean onDrag(View v, DragEvent event) { int action = event.getAction(); switch (action) { case DragEvent.ACTION_DRAG_STARTED: break; case DragEvent.ACTION_DRAG_ENTERED: v.setBackground(enterShape); break; case DragEvent.ACTION_DRAG_EXITED: v.setBackground(normalShape); break; case DragEvent.ACTION_DROP: View view = (View) event.getLocalState(); ViewGroup owner = (ViewGroup) view.getParent(); ViewGroup container = (ViewGroup) v; if (container.getClass() == FRAMELAYOUT_CLASS) { // If I could just get shadowBuilder here, I would be // able to retrieve its initial (x,y) offset // or its final (x,y) position, both work... view.setX(event.getX()); view.setY(event.getY()); } else if (container.getClass() == LINEARLAYOUT_CLASS) { // In a LinearLayout we remove any offset: view.setX(0); view.setY(0); } else return false; owner.removeView(view); container.addView(view); view.setVisibility(View.VISIBLE); break; case DragEvent.ACTION_DRAG_ENDED: v.setBackground(normalShape); default: break; } return true; } } </code></pre> <p>All that is set in the <code>OnCreate</code> method of the activity:</p> <pre class="lang-java prettyprint-override"><code>@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); View v = findViewById(R.id.view1); v.setOnTouchListener(new LongClickListener()); v = findViewById(R.id.view2); v.setOnTouchListener(new LongClickListener()); v = findViewById(R.id.frame); v.setOnDragListener(new DragListener()); v = findViewById(R.id.repository); v.setOnDragListener(new DragListener()); } </code></pre> <p>Thanks in advance for any tip on how I should get this information!</p> <hr> <p><strong>EDIT</strong>: Obviously I could pass the data in the ClipData but that would be awkward (especially if I need to pass larger data sets in the future, serialization is an overkill here):</p> <pre><code>ClipData data = ClipData.newPlainText( "pos", String.format("%d %d", (int)event.getX(), (int)event.getY())); v.startDrag(data, shadowBuilder, v, 0); </code></pre> <p>...</p> <pre><code>if (container.getClass() == FRAMELAYOUT_CLASS) { ClipData data = event.getClipData(); String[] pos = ((String)data.getItemAt(0).getText()).split(" "); int x = Integer.valueOf(pos[0]); int y = Integer.valueOf(pos[1]); view.setX(event.getX() - x); view.setY(event.getY() - y); </code></pre>
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