简介

其实要实现拖拽的控件是非常简单的事情，和让控件支持点击一样简单！

  1. 我们只需要实现onDragEvent() dispatchDragEvent() setOnDragListener()即可

    是不是和触摸事件的回调差不多呢？
    (onTouchEvent() dispatchTouchEvent() setOnTouchListener())

  2. 我们可以通过View.startDarg(ClipData data, DragShadowBuilder shadowBuilder, Object myLocalState, int flags)来开始拖拽

    • 这里需要我们传入一个 DragShadowBuilder 对象，DragShadow 就是拖拽阴影，会在你拖动的时候显示出来

Drag

实现

MainActivity.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
package cn.gavinliu.drag;

import android.app.Activity;
import android.content.ClipData;
import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.view.DragEvent;
import android.view.View;
import android.view.View.DragShadowBuilder;
import android.view.View.OnDragListener;
import android.view.View.OnLongClickListener;
import android.widget.ImageView;

public class MainActivity extends Activity {

    private String TAG = "DragDemo";

    private ImageView image;
    private ImageView image2;

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

        image = (ImageView) findViewById(R.id.image);
        image2 = (ImageView) findViewById(R.id.image2);

        image.setOnLongClickListener(new OnLongClickListener() {

            @Override
            public boolean onLongClick(View v) {
                // 创建DragShadowBuilder，我把控件本身传进去
                DragShadowBuilder builder = new DragShadowBuilder(v);
                // 剪切板数据，可以在DragEvent.ACTION_DROP方法的时候获取。
                ClipData data = ClipData.newPlainText("dot", "Dot : " + v.toString());
                // 开始拖拽
                v.startDrag(data, builder, v, 0);
                return true;
            }
        });

        image.setOnDragListener(new OnDragListener() {

            @Override
            public boolean onDrag(View v, DragEvent event) {
                final int action = event.getAction();
                switch (action) {
                // 开始拖拽
                case DragEvent.ACTION_DRAG_STARTED:
                    image.setVisibility(View.INVISIBLE);
                    Log.d(TAG, "image1 ACTION_DRAG_STARTED");
                    break;
                // 结束拖拽
                case DragEvent.ACTION_DRAG_ENDED:
                    image.setVisibility(View.VISIBLE);
                    Log.d(TAG, "image1 ACTION_DRAG_ENDED");
                    break;
                // 拖拽进某个控件后，退出
                case DragEvent.ACTION_DRAG_EXITED:
                    Log.d(TAG, "image1 ACTION_DRAG_EXITED");
                    break;
                // 拖拽进某个控件后，保持
                case DragEvent.ACTION_DRAG_LOCATION:
                    Log.d(TAG, "image1 ACTION_DRAG_LOCATION");
                    break;
                // 推拽进入某个控件
                case DragEvent.ACTION_DRAG_ENTERED:
                    Log.d(TAG, "image1 ACTION_DRAG_ENTERED");
                    break;
                // 推拽进入某个控件，后在该控件内，释放。即把推拽控件放入另一个控件
                case DragEvent.ACTION_DROP:
                    Log.d(TAG, "image1 ACTION_DROP");
                    break;
                }
                return true;
            }
        });

        image2.setOnDragListener(new OnDragListener() {

            @Override
            public boolean onDrag(View v, DragEvent event) {
                final int action = event.getAction();
                switch (action) {
                case DragEvent.ACTION_DRAG_STARTED:
                    Log.d(TAG, "image2 ACTION_DRAG_STARTED");
                    break;
                case DragEvent.ACTION_DRAG_ENDED:
                    image2.setBackgroundColor(Color.TRANSPARENT);
                    Log.d(TAG, "image2 ACTION_DRAG_ENDED");
                    break;
                case DragEvent.ACTION_DRAG_EXITED:
                    image2.setBackgroundColor(Color.TRANSPARENT);
                    Log.d(TAG, "image2 ACTION_DRAG_EXITED");
                    break;
                case DragEvent.ACTION_DRAG_ENTERED:
                    image2.setBackgroundColor(Color.BLUE);
                    Log.d(TAG, "image2 ACTION_DRAG_ENTERED");
                    break;
                case DragEvent.ACTION_DRAG_LOCATION:
                    Log.d(TAG, "image2 ACTION_DRAG_LOCATION");
                case DragEvent.ACTION_DROP:
                    Log.d(TAG, "image2 ACTION_DROP");
                }
                return true;
            }
        });
    }

}
activity_main.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/image"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:src="@drawable/ic_launcher" />

    <ImageView
        android:id="@+id/image2"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_alignParentRight="true"
        android:layout_below="@id/image"
        android:src="@drawable/ic_launcher" />

</RelativeLayout>

详细描述请参见官方文档：http://developer.android.com/guide/topics/ui/drag-drop.html