Android编程实现显示在标题上的进度条功能

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  android:id="@+id/main_layout" 
</LinearLayout 

public class MainActivity extends Activity {
  //图片id数组
  private int[] imageIds = { R.drawable.img01, R.drawable.img02,
      R.drawable.img03, R.drawable.img04 };
  private LinearLayout mainLayout;
  /**
   * Activity的入口方法
   */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //设置标题栏有进度条
    requestWindowFeature(Window.FEATURE_PROGRESS);
    setContentView(R.layout.activity_main);
    mainLayout = (LinearLayout)findViewById(R.id.main_layout);
    //实例化MyTask并开始执行
    new MyTask().execute();
  }
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
  }
  /**
   * 自定义继承AsyncTask的异步类MyTask
   */
  class MyTask extends AsyncTask<Void, Integer, LinearLayout {
    /**
     * 在doInBackground()方法之前执行的方法
     */
    @Override
    protected void onPreExecute() {
      super.onPreExecute();
      //设置标题栏的进度条可见
      setProgressBarVisibility(true);
    }
    /**
     * 后台执行的耗时操作
     */
    @Override
    protected LinearLayout doInBackground(Void... params) {
      LinearLayout ll = new LinearLayout(MainActivity.this);
      ll.setOrientation(LinearLayout.VERTICAL);
      ll.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
      for(int i=1; i<5; i++){
        ImageView iv = new ImageView(MainActivity.this);
        iv.setLayoutParams(new LayoutParams(200, 100));
        iv.setImageResource(imageIds[i-1]);
        ll.addView(iv);
        new Thread(){
          public void run() {
            try {
              //休眠20毫秒
              Thread.sleep(20);
            } catch (Exception e) {
              e.printStackTrace();
            }
          };
        }.start();
        //要求更新进度条，会引起调用onProgressUpdate()方法
        publishProgress(i);
      }
      return ll;
    }
    /**
     * 更新进度条
     */
    @Override
    protected void onProgressUpdate(Integer... values) {
      super.onProgressUpdate(values);
      //参数值为0-10000，所以要乘以2500，values[0]取值分别是1，2，3，4
      setProgress(values[0] * 2500);
    }
    /**
     * 后台操作执行完毕后所要执行的方法
     */
    @Override
    protected void onPostExecute(LinearLayout result) {
      super.onPostExecute(result);
      mainLayout.addView(result);
    }
  }
}