经常看到一些教程教你如何写appwidget，但是，你知道你的appwidget是如何被添加到桌面上的吗？
一般的，如果是做桌面的童鞋，基本上都会让自己的桌面支持appwidget。下面说说如何实现。
首先是得定义一个承载appwidget的容器，系统的Launcher里面是用的CellLayout，实现的很不错。我这里就用一个简单的自定义ViewGroup来搞定，它是以长按的坐标处为要添加的appwidget的起始位置，简单点说就是按到哪儿就添加到哪儿.
1.package chroya.demo.widget;
2.
3.import android.content.Context;
4.import android.view.MotionEvent;
5.import android.view.View;
6.import android.view.ViewGroup;
7.
8./**
9. * 承载widget的容器
10. * @author chroya
11. */
12.public class WidgetLayout extends ViewGroup {
13. //存放touch的坐标
14. private int [] cellInfo = new int [ 2 ];
15. private OnLongClickListener mLongClickListener;
16.
17. public WidgetLayout(Context context) {
18. super (context);
19. mLongClickListener = new OnLongClickListener() {
20.
21. @Override
22. public boolean onLongClick(View v) {
23.
24. return false ;
25. }
26. };
27. }
28.
29. public void addInScreen(View child, int width, int height) {
30. LayoutParams lp = new LayoutParams(width, height);
31. lp.x = cellInfo[0 ];
32. lp.y = cellInfo[1 ];
33. child.setOnLongClickListener(mLongClickListener);
34. addView(child, lp);
35. }
36.
37. @Override
38. protected void onMeasure( int widthMeasureSpec, int heightMeasureSpec) {
39. super .onMeasure(widthMeasureSpec, heightMeasureSpec);
40. LayoutParams lp;
41. for ( int index= 0 ; index<getChildCount(); index++) {
42. lp = (LayoutParams) getChildAt(index).getLayoutParams();
43. getChildAt(index).measure(
44. MeasureSpec.makeMeasureSpec(MeasureSpec.EXACTLY, lp.width),
45. MeasureSpec.makeMeasureSpec(MeasureSpec.EXACTLY, lp.height));
46. }
47. }
48.
49. @Override
50. public boolean dispatchTouchEvent(MotionEvent event) {
51. cellInfo[0 ] = ( int )event.getX();
52. cellInfo[1 ] = ( int )event.getY();
53. return super .dispatchTouchEvent(event);
54. }
55.
56. @Override
57. protected void onLayout( boolean changed, int l, int t, int r, int b) {
58. LayoutParams lp;
59. for ( int index= 0 ; index<getChildCount(); index++) {
60. lp = (LayoutParams) getChildAt(index).getLayoutParams();
61. getChildAt(index).layout(lp.x, lp.y, lp.x+lp.width, lp.y+lp.height);
62. }
63. }
64.
65. public static class LayoutParams extends ViewGroup.LayoutParams {
66. int x;
67. int y;
68.
69. public LayoutParams( int width, int height) {
70. super (width, height);
71. }
72. }
73.}
然后是重点了。还记得系统默认的桌面上，长按的时候出现的上下文菜单吗？里面有好几个选项，选择widget之后，会弹出一个已经安装的widget列表，选择一个widget之后，就会添加到桌面。我们可以把第一步去掉，长按之后，直接弹出已安装的widget列表，这是一个activity，用AppWidgetManager.ACTION_APPWIDGET_PICK这个Intent来启动，必须带上Extras，下面给出代码中有，不详叙。
1.package chroya.demo.widget;
2.
3.import static android.util.Log.d;
4.
5.import java.util.ArrayList;
6.
7.import android.app.Activity;
8.import android.appwidget.AppWidgetHost;
9.import android.appwidget.AppWidgetManager;
10.import android.appwidget.AppWidgetProviderInfo;
11.import android.content.ComponentName;
12.import android.content.Intent;
13.import android.os.Bundle;
14.import android.view.View;
15.import android.view.View.OnLongClickListener;
16.
17./**
18. * 添加appwidget
19. * @author chroya
20. *
21. */
22.public class Main extends Activity {
23. private AppWidgetHost mAppWidgetHost;
24. private AppWidgetManager mAppWidgetManager;
25. private WidgetLayout layout;
26.
27. private static final int REQUEST_PICK_APPWIDGET = 1 ;
28. private static final int REQUEST_CREATE_APPWIDGET = 2 ;
29. private static final int APPWIDGET_HOST_ID = 0x100 ;
30. private static final String EXTRA_CUSTOM_WIDGET = "custom_widget" ;
31.
32. @Override
33. public void onCreate(Bundle savedInstanceState) {
34. super .onCreate(savedInstanceState);
35.
36. mAppWidgetManager = AppWidgetManager.getInstance(getApplicationContext());
37. mAppWidgetHost = new AppWidgetHost(getApplicationContext(), APPWIDGET_HOST_ID);
38. //开始监听widget的变化
39. mAppWidgetHost.startListening();
40.
41. layout = new WidgetLayout( this );
42. layout.setOnLongClickListener(new OnLongClickListener() {
43.
44. @Override
45. public boolean onLongClick(View v) {
46.
47. addWidget();
48. return false ;
49. }
50. });
51. setContentView(layout);
52. }
53.
54. @Override
55. protected void onActivityResult( int requestCode, int resultCode, Intent data) {
56. if (resultCode == RESULT_OK) {
57. switch (requestCode) {
58. case REQUEST_PICK_APPWIDGET:
59. addAppWidget(data);
60. break ;
61. case REQUEST_CREATE_APPWIDGET:
62. completeAddAppWidget(data);
63. break ;
64. }
65. } else if (requestCode == REQUEST_PICK_APPWIDGET &&
66. resultCode == RESULT_CANCELED && data != null ) {
67. // Clean up the appWidgetId if we canceled
68. int appWidgetId = data.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, - 1 );
69. if (appWidgetId != - 1 ) {
70. mAppWidgetHost.deleteAppWidgetId(appWidgetId);
71. }
72. }
73. }
74.
75. /**
76. * 选中了某个widget之后，根据是否有配置来决定直接添加还是弹出配置activity
77. * @param data
78. */
79. private void addAppWidget(Intent data) {
80. int appWidgetId = data.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, - 1 );
81.
82. String customWidget = data.getStringExtra(EXTRA_CUSTOM_WIDGET);
83. d("addAppWidget" , "data:" + customWidget);
84. if ( "search_widget" .equals(customWidget)) {
85. //这里直接将search_widget删掉了
86. mAppWidgetHost.deleteAppWidgetId(appWidgetId);
87. } else {
88. AppWidgetProviderInfo appWidget = mAppWidgetManager.getAppWidgetInfo(appWidgetId);
89.
90. d("addAppWidget" , "configure:" + appWidget.configure);
91. if (appWidget.configure != null ) {
92. //有配置，弹出配置
93. Intent intent = new Intent(AppWidgetManager.ACTION_APPWIDGET_CONFIGURE);
94. intent.setComponent(appWidget.configure);
95. intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);
96.
97. startActivityForResult(intent, REQUEST_CREATE_APPWIDGET);
98. } else {
99. //没有配置，直接添加
100. onActivityResult(REQUEST_CREATE_APPWIDGET, Activity.RESULT_OK, data);
101. }
102. }
103. }
104.
105. /**
106. * 请求添加一个新的widget
107. */
108. private void addWidget() {
109. int appWidgetId = mAppWidgetHost.allocateAppWidgetId();
110.
111. Intent pickIntent = new Intent(AppWidgetManager.ACTION_APPWIDGET_PICK);
112. pickIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);
113. // add the search widget
114. ArrayList<AppWidgetProviderInfo> customInfo =
115. new ArrayList<AppWidgetProviderInfo>();
116. AppWidgetProviderInfo info = new AppWidgetProviderInfo();
117. info.provider = new ComponentName(getPackageName(), "XXX.YYY" );
118. info.label = "Search" ;
119. info.icon = R.drawable.ic_search_widget;
120. customInfo.add(info);
121. pickIntent.putParcelableArrayListExtra(
122. AppWidgetManager.EXTRA_CUSTOM_INFO, customInfo);
123. ArrayList<Bundle> customExtras = new ArrayList<Bundle>();
124. Bundle b = new Bundle();
125. b.putString(EXTRA_CUSTOM_WIDGET, "search_widget" );
126. customExtras.add(b);
127. pickIntent.putParcelableArrayListExtra(
128. AppWidgetManager.EXTRA_CUSTOM_EXTRAS, customExtras);
129. // start the pick activity
130. startActivityForResult(pickIntent, REQUEST_PICK_APPWIDGET);
131. }
132.
133. /**
134. * 添加widget
135. * @param data
136. */
137. private void completeAddAppWidget(Intent data) {
138. Bundle extras = data.getExtras();
139. int appWidgetId = extras.getInt(AppWidgetManager.EXTRA_APPWIDGET_ID, - 1 );
140.
141. d("completeAddAppWidget" , "dumping extras content=" +extras.toString());
142. d("completeAddAppWidget" , "appWidgetId:" + appWidgetId);
143. AppWidgetProviderInfo appWidgetInfo = mAppWidgetManager.getAppWidgetInfo(appWidgetId);
144.
145. View hostView = mAppWidgetHost.createView(this , appWidgetId, appWidgetInfo);
146.
147. layout.addInScreen(hostView, appWidgetInfo.minWidth, appWidgetInfo.minHeight);
148. }
149.}
需要注意的几点：
1。 必须调用AppWidgetHost的startListening方法来监听appwidget的状态变化，否则添加上去的appwidget不会更新的。
2。 需要override一个onActivityResult方法，来接收添加appwidget和appwidget的配置activity的返回值。
3。 启动AppWidgetManager.ACTION_APPWIDGET_PICK这个Intent，必须要给列表中加上自己定义的一个选项，否则出错。如本例中是用的Search。