android.app包中含有一個ActivityGroup類，該類是Activity的容器，可以包含多個嵌套進來的Activitys，這篇文章就是借助ActivityGroup可以嵌套Activity的功能來實現Tab功能。tab這種UI在很多的移動應用中可以看到，包括android、iphone、window phone7等移動終端上都有這樣的應用，Tab這種UI方式具有小視圖大容量的特點。
首先，從SDK中doc文檔中都可以獲知，ActivityGroup類的父類是Activity（見下圖），也就是說二者具有相同的接口和生命周期，同Activity一樣，也有onCreate()、onPause()等函數可供我們重載。

ActivityGroup中有兩個public方法（下圖）：ActivityGroup中可以調用getLocalActivityManage（）方法獲取LocalActityManage來管理Activity。

ActivityGroup實現的tab功能的效果圖如下。

先看一下java代碼：

1. public class MainView extends ActivityGroup {
2. @SuppressWarnings ( “unused” )
3. private LinearLayout bodyView , headview ;
4. private LinearLayout one , two , three , four ;
5. private int flag = 0 ; // 通過標記跳轉不同的頁面，顯示不同的菜單項
6. /** Called when the activity is first created. */
7. @Override
8. public void onCreate ( Bundle savedInstanceState ) {
9. super . onCreate ( savedInstanceState );
10. setContentView ( R . layout . view_main );
11. initMainView ();
12. // 顯示標記頁面
13. showView ( flag );
14. one . setOnClickListener ( new OnClickListener () {
15. public void onClick ( View v ) {
16. // TODO Auto-generated method stub
17. flag = 0 ;
18. showView ( flag );
19. }
20. });
21. two . setOnClickListener ( new OnClickListener () {
22. public void onClick ( View v ) {
23. // TODO Auto-generated method stub
24. flag = 1 ;
25. showView ( flag );
26. }
27. });
28. three . setOnClickListener ( new OnClickListener () {
29. public void onClick ( View v ) {
30. // TODO Auto-generated method stub
31. flag = 2 ;
32. showView ( flag );
33. }
34. });
35. four . setOnClickListener ( new OnClickListener () {
36. public void onClick ( View v ) {
37. // TODO Auto-generated method stub
38. flag = 3 ;
39. showView ( flag );
40. }
41. });
43. }
45. /*
46. * 初始化主界面
47. */
48. public void initMainView () {
49. headview =( LinearLayout ) findViewById ( R . id . head );
50. bodyView =( LinearLayout ) findViewById ( R . id . body );
51. one =( LinearLayout ) findViewById ( R . id . one );
52. two =( LinearLayout ) findViewById ( R . id . two );
53. three =( LinearLayout ) findViewById ( R . id . three );
54. four =( LinearLayout ) findViewById ( R . id . four );
55. }
57. // 在主界面中顯示其他界面
58. public void showView ( int flag ) {
59. switch ( flag ) {
60. case 0 :
61. bodyView . removeAllViews ();
62. View v = getLocalActivityManager (). startActivity ( “one” ,
63. new Intent ( MainView . this , OneView . class )). getDecorView ();
65. one . setBackgroundResource ( R . drawable . frame_button_background );
66. two . setBackgroundResource ( R . drawable . frame_button_nopressbg );
67. three . setBackgroundResource ( R . drawable . frame_button_nopressbg );
68. four . setBackgroundResource ( R . drawable . frame_button_nopressbg );
70. bodyView . addView ( v );
71. break ;
72. case 1 :
73. bodyView . removeAllViews ();
74. bodyView . addView ( getLocalActivityManager (). startActivity ( “two” ,
75. new Intent ( MainView . this , TwoView . class ))
76. . getDecorView ());
77. one . setBackgroundResource ( R . drawable . frame_button_nopressbg );
78. two . setBackgroundResource ( R . drawable . frame_button_background );
79. three . setBackgroundResource ( R . drawable . frame_button_nopressbg );
80. four . setBackgroundResource ( R . drawable . frame_button_nopressbg );
81. break ;
82. case 2 :
83. bodyView . removeAllViews ();
84. bodyView . addView ( getLocalActivityManager (). startActivity (
85. “three” , new Intent ( MainView . this , ThreeView . class ))
86. . getDecorView ());
87. one . setBackgroundResource ( R . drawable . frame_button_nopressbg );
88. two . setBackgroundResource ( R . drawable . frame_button_nopressbg );
89. three . setBackgroundResource ( R . drawable . frame_button_background );
90. four . setBackgroundResource ( R . drawable . frame_button_nopressbg );
91. break ;
92. case 3 :
93. bodyView . removeAllViews ();
94. bodyView . addView ( getLocalActivityManager (). startActivity (
95. “four” , new Intent ( MainView . this , FourView . class ))
96. . getDecorView ());
97. one . setBackgroundResource ( R . drawable . frame_button_nopressbg );
98. two . setBackgroundResource ( R . drawable . frame_button_nopressbg );
99. three . setBackgroundResource ( R . drawable . frame_button_nopressbg );
100. four . setBackgroundResource ( R . drawable . frame_button_background );
101. break ;
102. default :
103. break ;
104. }
105. }
106. }

程序中重要的是如下的方法：

1. bodyView . removeAllViews ();
2. bodyView . addView ( getLocalActivityManager (). startActivity ( “two” ,
3. new Intent ( MainView . this , TwoView . class ))
4. . getDecorView ());

使用view的removeAllViews()方法清除不需要的view，使用addView(View v)方法添加需要的view。

getLocalActivityManager().startActivity(“two”,new Intent(MainView.this, TwoView.class))得到一個window對象，window對象調用

getDecorView()獲取view。關于window的方法可以參考android.app.Window。

通過tab的效果圖可以看到這個效果使用了上、中、下三種布局，layout就可以這樣做了。實現layout就可以實現tab功能了。

Android UI開發第十八篇——ActivityGroup實現tab功能