1. 引言：

为了提高ListView的效率和应用程序的性能，在Android应用程序中不应该一次性载入ListView所要显示的全部信息，而是采取分批载入策略，随著用户的滑动，动态的从后台载入所需的数据，并渲染到ListView组件中，这样可以极大的改善应用程序的性能和用户体验。2. 交互：

进入ListView组件，首先预载入N条记录，当用户滑动到最后一条记录显示载入提示信息，并从后台载入N条数据，接著渲染UI界面。3. 效果图：

4. 程序实现： view plaincopy to clipboard

1. packagecom.focus.loading;
2. importandroid.app.ListActivity;
3. importandroid.os.Bundle;
4. importandroid.os.Handler;
5. importandroid.view.Gravity;
6. importandroid.view.View;
7. importandroid.view.ViewGroup;
8. importandroid.widget.AbsListView;
9. importandroid.widget.BaseAdapter;
10. importandroid.widget.LinearLayout;
11. importandroid.widget.ListView;
12. importandroid.widget.ProgressBar;
13. importandroid.widget.TextView;
14. importandroid.widget.AbsListView.OnScrollListener;
15. importandroid.widget.LinearLayout.LayoutParams;
16. publicclassListViewLoadingActivityextendsListActivityimplements
17. OnScrollListener{
18. @Override
19. publicvoidonCreate(BundlesavedInstanceState){
20. super.onCreate(savedInstanceState);
21. /**
22. *"载入项"布局，此布局被添加到ListView的Footer中。
23. */
24. mLoadLayout=newLinearLayout(this);
25. mLoadLayout.setMinimumHeight(60);
26. mLoadLayout.setGravity(Gravity.CENTER);
27. mLoadLayout.setOrientation(LinearLayout.HORIZONTAL);
28. /**
29. *向"载入项"布局中添加一个圆型进度条。
30. */
31. ProgressBarmProgressBar=newProgressBar(this);
32. mProgressBar.setPadding(0,0,15,0);
33. mLoadLayout.addView(mProgressBar,mProgressBarLayoutParams);
34. /**
35. *向"载入项"布局中添加提示信息。
36. */
37. TextViewmTipContent=newTextView(this);
38. mTipContent.setText("载入中...");
39. mLoadLayout.addView(mTipContent,mTipContentLayoutParams);
40. /**
41. *获取ListView组件，并将"载入项"布局添加到ListView组件的Footer中。
42. */
43. mListView=getListView();
44. mListView.addFooterView(mLoadLayout);
45. /**
46. *组ListView组件设置Adapter,并设置滑动监听事件。
47. */
48. setListAdapter(mListViewAdapter);
49. mListView.setOnScrollListener(this);
50. }
51. publicvoidonScroll(AbsListViewview,intmFirstVisibleItem,
52. intmVisibleItemCount,intmTotalItemCount){
53. mLastItem=mFirstVisibleItem+mVisibleItemCount-1;
54. if(mListViewAdapter.count>mCount){
55. mListView.removeFooterView(mLoadLayout);
56. }
57. }
58. publicvoidonScrollStateChanged(AbsListViewview,intmScrollState){
60. /**
61. *当ListView滑动到最后一条记录时这时，我们会看到已经被添加到ListView的"载入项"布局，这时应该载入剩余数据。
62. */
63. if(mLastItem==mListViewAdapter.count
64. &&mScrollState==OnScrollListener.SCROLL_STATE_IDLE){
65. if(mListViewAdapter.count<=mCount){
66. mHandler.postDelayed(newRunnable(){
67. @Override
68. publicvoidrun(){
69. mListViewAdapter.count+=10;
70. mListViewAdapter.notifyDataSetChanged();
71. mListView.setSelection(mLastItem);
72. }
73. },1000);
74. }
75. }
76. }
77. classListViewAdapterextendsBaseAdapter{
78. intcount=10;
79. publicintgetCount(){
80. returncount;
81. }
82. publicObjectgetItem(intposition){
83. returnposition;
84. }
85. publiclonggetItemId(intposition){
86. returnposition;
87. }
88. publicViewgetView(intposition,Viewview,ViewGroupparent){
89. TextViewmTextView;
90. if(view==null){
91. mTextView=newTextView(ListViewLoadingActivity.this);
92. }else{
93. mTextView=(TextView)view;
94. }
95. mTextView.setText("Item"+position);
96. mTextView.setTextSize(20f);
97. mTextView.setGravity(Gravity.CENTER);
98. mTextView.setHeight(60);
99. returnmTextView;
100. }
101. }
102. privateLinearLayoutmLoadLayout;
103. privateListViewmListView;
104. privateListViewAdaptermListViewAdapter=newListViewAdapter();
105. privateintmLastItem=0;
106. privateintmCount=41;
107. privatefinalHandlermHandler=newHandler();
108. privatefinalLayoutParamsmProgressBarLayoutParams=newLinearLayout.LayoutParams(
109. LinearLayout.LayoutParams.WRAP_CONTENT,
110. LinearLayout.LayoutParams.WRAP_CONTENT);
111. privatefinalLayoutParamsmTipContentLayoutParams=newLinearLayout.LayoutParams(
112. LinearLayout.LayoutParams.WRAP_CONTENT,
113. LinearLayout.LayoutParams.WRAP_CONTENT);
114. }

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