/**
 * 透明度可變的標(biāo)題欄
 * 
 * @author Zhao KaiQiang
 * 
 * @Time 2014-6-20 上午11:46:42
 */
public class MainActivity extends Activity implements OnScrollListener {

 private XListView listView;
 // 標(biāo)題欄的布局
 private RelativeLayout rl_title;
 // ListView的頭布局
 private View headerView;
 // 頭布局的高度
 private int headerHeight;
 private LayoutInflater inflater;
 private Handler handler = new Handler();

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

 rl_title = (RelativeLayout) findViewById(R.id.rl_title);
 listView = (XListView) findViewById(R.id.list);

 rl_title.getBackground().setAlpha(0);
 inflater = LayoutInflater.from(this);
 headerView = inflater.inflate(R.layout.header_listview, null);
 // 添加頭布局
 listView.addHeaderView(headerView);
 listView.setAdapter(new MyAdapter());
 // 設(shè)置滾動監(jiān)聽
 listView.setOnScrollListener(this);
 // 設(shè)置可以刷新與加載更多
 listView.setPullLoadEnable(true);
 listView.setPullRefreshEnable(true);
 listView.setXListViewListener(new IXListViewListener() {

  @Override
  public void onRefresh() {
  // 單純的模擬刷新過程
  handler.postDelayed(new Runnable() {

   @Override
   public void run() {
   listView.stopRefresh();
   }
  }, 500);
  }

  @Override
  public void onLoadMore() {
  // 單純的模擬加載過程
  handler.postDelayed(new Runnable() {

   @Override
   public void run() {
   listView.stopLoadMore();
   }
  }, 500);
  }
 });

 }

 // 自定義適配器
 private class MyAdapter extends BaseAdapter {

 // 默認(rèn)顯示10個(gè)item
 @Override
 public int getCount() {
  return 10;
 }

 @Override
 public Object getItem(int position) {
  return position;
 }

 @Override
 public long getItemId(int position) {
  return position;
 }

 @Override
 public View getView(int position, View convertView, ViewGroup parent) {
  if (convertView == null) {
  convertView = inflater.inflate(R.layout.item_list, null);
  }

  return convertView;
 }

 }

 @Override
 public void onScrollStateChanged(AbsListView view, int scrollState) {

 }

 // 最重要的方法，標(biāo)題欄的透明度變化在這個(gè)方法實(shí)現(xiàn)
 @Override
 public void onScroll(AbsListView listView, int firstVisibleItem,
  int visibleItemCount, int totalItemCount) {
 // 判斷當(dāng)前最上面顯示的是不是頭布局，因?yàn)閄listview有刷新控件，所以頭布局的位置是1，即第二個(gè)
 if (firstVisibleItem == 1) {
  // 獲取頭布局
  View view = listView.getChildAt(0);
  if (view != null) {
  // 獲取頭布局現(xiàn)在的最上部的位置的相反數(shù)
  int top = -view.getTop();
  // 獲取頭布局的高度
  headerHeight = view.getHeight();
  // 滿足這個(gè)條件的時(shí)候，是頭布局在XListview的最上面第一個(gè)控件的時(shí)候，只有這個(gè)時(shí)候，我們才調(diào)整透明度
  if (top <= headerHeight && top >= 0) {
   // 獲取當(dāng)前位置占頭布局高度的百分比
   float f = (float) top / (float) headerHeight;
   rl_title.getBackground().setAlpha((int) (f * 255));
   // 通知標(biāo)題欄刷新顯示
   rl_title.invalidate();
  }
  }
 } else if (firstVisibleItem > 1) {
  rl_title.getBackground().setAlpha(255);
 } else {
  rl_title.getBackground().setAlpha(0);
 }
 }

}