Introduce Drag And Drop for Android 3.0+

Start from Android 3.0, API Level 11, Android support Drag and Drop natually. With the Android drag/drop framework, you can allow your users to move data from one View to another View in the current layout using a graphical drag and drop gesture. The framework includes a drag event class, drag listeners, and helper methods and classes.

It's a example show how to handle the basic operation of Drag And Drop. User can drag the button1~4 over buttonTarget. As a example, it do nothing except display the events in a TextView.



A common View.OnDragListener, MyDragEventListener, is implement for all view listen to the Darg and Drop operation.

When a view (button1~4) is onLongClick, it start the Drag And Drop by calling startDrag().

Then a event of ACTION_DRAG_STARTED will be passed to the OnDragListener of all view with setOnDragListener. In order to accept it, all view should return true; otherwise it will not receive any other event in current Drap And Drop operation.

When user Drop it on any involved view, event of ACTION_DROP will be passed to the landing view. And finally, ACTION_END will passed to all involved views.

package com.exercise.com;

import android.app.Activity;
import android.content.ClipData;
import android.content.ClipDescription;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Point;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.DragEvent;
import android.view.View;
import android.view.View.DragShadowBuilder;
import android.widget.Button;
import android.widget.TextView;

public class AndroidDragAndDropActivity extends Activity {

Button button1, button2, button3, button4, buttonTarget;
Button dragSourceButton;
TextView comments;

String commentMsg;

MyDragEventListener myDragEventListener = new MyDragEventListener();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    button1 = (Button)findViewById(R.id.button1);
    button2 = (Button)findViewById(R.id.button2);
    button3 = (Button)findViewById(R.id.button3);
    button4 = (Button)findViewById(R.id.button4);
    buttonTarget = (Button)findViewById(R.id.buttonTarget);
    comments = (TextView)findViewById(R.id.comments);

    // Create and set the tags for the Buttons
    final String BUTTON1_TAG = "button1";
    final String BUTTON2_TAG = "button2";
    final String BUTTON3_TAG = "button3";
    final String BUTTON4_TAG = "button4";
    button1.setTag(BUTTON1_TAG);
    button2.setTag(BUTTON2_TAG);
    button3.setTag(BUTTON3_TAG);
    button4.setTag(BUTTON4_TAG);

    button1.setOnLongClickListener(sourceButtonsLongClickListener);
    button2.setOnLongClickListener(sourceButtonsLongClickListener);
    button3.setOnLongClickListener(sourceButtonsLongClickListener);
    button4.setOnLongClickListener(sourceButtonsLongClickListener);

    button1.setOnDragListener(myDragEventListener);
    button2.setOnDragListener(myDragEventListener);
    button3.setOnDragListener(myDragEventListener);
    button4.setOnDragListener(myDragEventListener);
    buttonTarget.setOnDragListener(myDragEventListener);
}

Button.OnLongClickListener sourceButtonsLongClickListener
= new Button.OnLongClickListener(){

 @Override
 public boolean onLongClick(View v) {
  ClipData.Item item = new ClipData.Item((CharSequence)v.getTag());
  String[] clipDescription = {ClipDescription.MIMETYPE_TEXT_PLAIN};
  ClipData dragData = new ClipData((CharSequence)v.getTag(),
    clipDescription,
    item);
  DragShadowBuilder myShadow = new MyDragShadowBuilder(v);
 
  v.startDrag(dragData,
                myShadow,
                null,
                0);
 
  commentMsg = v.getTag() + " : onLongClick.\n";
  comments.setText(commentMsg);
 
  return true;
 }};

private static class MyDragShadowBuilder extends View.DragShadowBuilder {
 private static Drawable shadow;

 public MyDragShadowBuilder(View v) {
  super(v);
  shadow = new ColorDrawable(Color.LTGRAY);
    }

 @Override
    public void onProvideShadowMetrics (Point size, Point touch){
        int width = getView().getWidth();
        int height = getView().getHeight();

        shadow.setBounds(0, 0, width, height);
        size.set(width, height);
        touch.set(width / 2, height / 2);
    }

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

}

protected class MyDragEventListener implements View.OnDragListener {

 @Override
 public boolean onDrag(View v, DragEvent event) {
  final int action = event.getAction();
 
  switch(action) {
  case DragEvent.ACTION_DRAG_STARTED:
   //All involved view accept ACTION_DRAG_STARTED for MIMETYPE_TEXT_PLAIN
            if (event.getClipDescription()
              .hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN))
            {
             commentMsg += ((Button)v).getText()
               + " : ACTION_DRAG_STARTED accepted.\n";
             comments.setText(commentMsg);
             return true; //Accept
            }else{
             commentMsg += ((Button)v).getText()
               + " : ACTION_DRAG_STARTED rejected.\n";
             comments.setText(commentMsg);
             return false; //reject
            }
  case DragEvent.ACTION_DRAG_ENTERED:
   commentMsg += ((Button)v).getText() + " : ACTION_DRAG_ENTERED.\n";
   comments.setText(commentMsg);
   return true;
  case DragEvent.ACTION_DRAG_LOCATION:
   commentMsg += ((Button)v).getText() + " : ACTION_DRAG_LOCATION - "
    + event.getX() + " : " + event.getY() + "\n";
   comments.setText(commentMsg);
   return true;
  case DragEvent.ACTION_DRAG_EXITED:
   commentMsg += ((Button)v).getText() + " : ACTION_DRAG_EXITED.\n";
   comments.setText(commentMsg);
   return true;
  case DragEvent.ACTION_DROP:
   // Gets the item containing the dragged data
            ClipData.Item item = event.getClipData().getItemAt(0);

            commentMsg += ((Button)v).getText() + " : ACTION_DROP"
              + " - from " + item.getText().toString() + "\n";
   comments.setText(commentMsg);
        
            return true;
  case DragEvent.ACTION_DRAG_ENDED:
   if (event.getResult()){
    commentMsg += ((Button)v).getText() + " : ACTION_DRAG_ENDED - success.\n";
    comments.setText(commentMsg);
   } else {
    commentMsg += ((Button)v).getText() + " : ACTION_DRAG_ENDED - fail.\n";
    comments.setText(commentMsg);
   };
            return true;
  default: //unknown case
   commentMsg += ((Button)v).getText() + " : UNKNOWN !!!\n";
   comments.setText(commentMsg);
   return false;

  }

 }}

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello" />
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Drag Source" />
<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal" >
    <Button
        android:id="@+id/button1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="#FF0000"
        android:text="Red" />
    <Button
        android:id="@+id/button2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="#00FF00"
        android:text="Green" />
    <Button
        android:id="@+id/button3"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="#0000FF"
        android:text="Blue" />
    <Button
        android:id="@+id/button4"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="#A0A0A0"
        android:text="Gray" />
</LinearLayout>
<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/ic_launcher" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Drop Target"
    android:layout_gravity="center" />
<Button
        android:id="@+id/buttonTarget"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:background="#404040"
        android:text="Dark Gray" />
<ScrollView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView
        android:id="@+id/comments"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
</ScrollView>
</LinearLayout>

Download the files.

Next:
- Passing object in Drap And Drop using myLocalState