Android-在应用中使用拖拽教程

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该教程介绍了如何在Android 4.0及更高版本中实现视图的拖放功能，包括启用视图拖放、定义拖放目标，并提供了一个练习来创建允许相互拖放的多个视图组。

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Android-在应用中使用拖拽教程

Lars Vogel

Version 1.3
Copyright © 2012-2014 vogella GmbH
21.11.2014
在Android中使用拖拽

这个教程描述在Android中如何使用拖拽

Android拖拽
1.1在Android中使用拖拽
1.2允许view拖拽
1.3定义拖动目标
练习：拖拽
2.1这个练习的目标
2.2创建项目
2.3创建 xml Drawable
2.4Activity和layout

1.Android拖拽

1.1在Android中使用拖拽
Android4.0支持在view或viewGroup上的拖拽view
1.2允许view拖拉
你注册一个onTouchListener或LongClickListener在被拖拽的view上使其能够拖拽
View的startDrag方法开始一个拖拽操作。在这个方法你也可以通过ClipData的实例指定按下拖拽目标数据
你也可以通过DragShadowBuilder实例的startDrag方法。这个对象指定图像用于拖拽操作。例如你可以直接地通过View，在拖拽操作中展现一个view的图像
下面的例子演示在TouchListener下的拖拉操作设置

    // Assign the touch listener to your view which you want to move
            findViewById(R.id.myimage1).setOnTouchListener(new MyTouchListener());

    // This defines your touch listener
    private final class MyTouchListener implements OnTouchListener {
      public boolean onTouch(View view, MotionEvent motionEvent) {
if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
  ClipData data = ClipData.newPlainText("", "");
  DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
  view.startDrag(data, shadowBuilder, view, 0);
  view.setVisibility(View.INVISIBLE);
  return true;
} else {
return false;
}
     }
    }

1.3 定义拖拉目标

能够拖拽的view得到一个onDragListener分配的实例。在这个拖拽监听，你接收预定义的拖拽相关事件回调

DragEvent.ACTION_DRAG_STARTED
DragEvent.ACTION_DRAG_ENTERED
DragEvent.ACTION_DRAG_EXITED
DragEvent.ACTION_DROP

DragEvent.ACTION_DRAG_ENDED
一个有onDragListener的view是可以拖拽的区域，通过setonDragListener得到一个分配onDragListener

 findViewById(R.id.bottomright).setOnDragListener(new MyDragListener());

class MyDragListener implements OnDragListener {
  Drawable enterShape = getResources().getDrawable(R.drawable.shape_droptarget);
  Drawable normalShape = getResources().getDrawable(R.drawable.shape);

  @Override
  public boolean onDrag(View v, DragEvent event) {
    int action = event.getAction();
    switch (event.getAction()) {
    case DragEvent.ACTION_DRAG_STARTED:
// do nothing
  break;
  case DragEvent.ACTION_DRAG_ENTERED:
    v.setBackgroundDrawable(enterShape);
    break;
  case DragEvent.ACTION_DRAG_EXITED:        
    v.setBackgroundDrawable(normalShape);
    break;
  case DragEvent.ACTION_DROP:
    // Dropped, reassign View to ViewGroup
    View view = (View) event.getLocalState();
            ViewGroup owner = (ViewGroup) view.getParent();
    owner.removeView(view);
    LinearLayout container = (LinearLayout) v;
    container.addView(view);
    view.setVisibility(View.VISIBLE);
    break;
  case DragEvent.ACTION_DRAG_ENDED:
    v.setBackgroundDrawable(normalShape);
    default:
    break;
  }
  return true;
}
}

练习：拖拽

2.1练习目标
在这个练习中，你创建多个允许他们之间拖动views的Viewgroup
2.2创建项目
创建一个新的名为com.vogella.android.draganddrop的Android 项目和一个叫DragActivity的Activity
创建 XMLDrawables
在这个练习你能够使用 XML Drawable
在这个部分你在res/drawable文件夹创建多个XML Drawable
创建下面shape.xml文件在这个文件夹

    <?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle" >

<stroke
    android:width="2dp"
    android:color="#FFFFFFFF" />

<gradient
    android:angle="225"
    android:endColor="#DD2ECCFA"
    android:startColor="#DD000000" />

<corners
    android:bottomLeftRadius="7dp"
    android:bottomRightRadius="7dp"
    android:topLeftRadius="7dp"
    android:topRightRadius="7dp" />

  </shape>

也创建下面的shape——droptarget.xml文件

<?xml version="1.0" encoding="UTF-8"?>
 <shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle" >

<stroke
    android:width="2dp"
    android:color="#FFFF0000" />

<gradient
    android:angle="225"
    android:endColor="#DD2ECCFA"
    android:startColor="#DD000000" />

<corners
    android:bottomLeftRadius="7dp"
    android:bottomRightRadius="7dp"
    android:topLeftRadius="7dp"
    android:topRightRadius="7dp" />

  </shape>

2.4Activity和layout
用下面的代码的修改Activity的layout

        <?xml version="1.0" encoding="utf-8"?>
    <GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:columnCount="2"
android:columnWidth="320dp"
android:orientation="vertical"
android:rowCount="2"
android:stretchMode="columnWidth" >

<LinearLayout
    android:id="@+id/topleft"
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:layout_row="0"
    android:background="@drawable/shape" >

    <ImageView
        android:id="@+id/myimage1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />
</LinearLayout>

<LinearLayout
    android:id="@+id/topright"
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:background="@drawable/shape" >

    <ImageView
        android:id="@+id/myimage2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />
</LinearLayout>

<LinearLayout
    android:id="@+id/bottomleft"
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:background="@drawable/shape" >

    <ImageView
        android:id="@+id/myimage3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />
</LinearLayout>

<LinearLayout
    android:id="@+id/bottomright"
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:background="@drawable/shape" >

    <ImageView
        android:id="@+id/myimage4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />
</LinearLayout>

</GridLayout>

用下面的代码修改你的activity

        package com.vogella.android.draganddrop;

import android.app.Activity;
import android.content.ClipData;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.DragEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.DragShadowBuilder;
import android.view.View.OnDragListener;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.widget.LinearLayout;

public class DragActivity extends Activity {

/** Called when the activity is first created. */

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    findViewById(R.id.myimage1).setOnTouchListener(new MyTouchListener());
    findViewById(R.id.myimage2).setOnTouchListener(new MyTouchListener());
    findViewById(R.id.myimage3).setOnTouchListener(new MyTouchListener());
    findViewById(R.id.myimage4).setOnTouchListener(new MyTouchListener());
    findViewById(R.id.topleft).setOnDragListener(new MyDragListener());
    findViewById(R.id.topright).setOnDragListener(new MyDragListener());
    findViewById(R.id.bottomleft).setOnDragListener(new MyDragListener());
    findViewById(R.id.bottomright).setOnDragListener(new MyDragListener());

  }

  private final class MyTouchListener implements OnTouchListener {
    public boolean onTouch(View view, MotionEvent motionEvent) {
      if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
        ClipData data = ClipData.newPlainText("", "");
        DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
        view.startDrag(data, shadowBuilder, view, 0);
        view.setVisibility(View.INVISIBLE);
        return true;
      } else {
        return false;
      }
    }
  }

  class MyDragListener implements OnDragListener {
    Drawable enterShape = getResources().getDrawable(R.drawable.shape_droptarget);
    Drawable normalShape = getResources().getDrawable(R.drawable.shape);

@Override
public boolean onDrag(View v, DragEvent event) {
  int action = event.getAction();
  switch (event.getAction()) {
  case DragEvent.ACTION_DRAG_STARTED:
    // do nothing
    break;
  case DragEvent.ACTION_DRAG_ENTERED:
    v.setBackgroundDrawable(enterShape);
    break;
  case DragEvent.ACTION_DRAG_EXITED:
    v.setBackgroundDrawable(normalShape);
    break;
  case DragEvent.ACTION_DROP:
    // Dropped, reassign View to ViewGroup
    View view = (View) event.getLocalState();
    ViewGroup owner = (ViewGroup) view.getParent();
    owner.removeView(view);
    LinearLayout container = (LinearLayout) v;
    container.addView(view);
    view.setVisibility(View.VISIBLE);
    break;
  case DragEvent.ACTION_DRAG_ENDED:
    v.setBackgroundDrawable(normalShape);
  default:
    break;
  }
  return true;
}
  }
}

如果你开启这个activity，你应该能够拖动ImageView到其他容
这里写图片描述
原文地址