public void onBackPressed() {    //Preferences 中獲取是否雙擊退出    boolean isDoubleClick = true;    //BaseApplication.get("ifDoubleClickedBack", true);    if (isDoubleClick) {      long curTime = SystemClock.uptimeMillis();      if ((curTime - mBackPressedTime) < (2 * 1000)) {        finish();        //activity棧管理        AppManager.getAppManager().AppExit();      } else {        mBackPressedTime = curTime;        Toast.makeText(this, "再次點擊退出", Toast.LENGTH_SHORT).show();      }    } else {      finish();    }  }

public class AppManager {  private static Stack<Activity> activityStack;  private static AppManager instance;  private AppManager() {  }  /**   * 單一實例   */  public static AppManager getAppManager() {    if (instance == null) {      instance = new AppManager();    }    if (activityStack == null) {      activityStack = new Stack<Activity>();    }    return instance;  }  /**   * 獲取指定的Activity   *   * @author kymjs   */  public static Activity getActivity(Class<?> cls) {    if (activityStack != null)      for (Activity activity : activityStack) {        if (activity.getClass().equals(cls)) {          return activity;        }      }    return null;  }  /**   * 添加Activity到堆棧   */  public void addActivity(Activity activity) {    activityStack.add(activity);  }  /**   * 獲取當前Activity（堆棧中最后一個壓入的）   */  public Activity currentActivity() {    Activity activity = activityStack.lastElement();    return activity;  }  /**   * 結束當前Activity（堆棧中最后一個壓入的）   */  public void finishActivity() {    Activity activity = activityStack.lastElement();    finishActivity(activity);  }  /**   * 結束指定的Activity   */  public void finishActivity(Activity activity) {    if (activity != null && activityStack.contains(activity)) {      activityStack.remove(activity);      activity.finish();    }  }  /**   * 結束指定的Activity   */  public void removeActivity(Activity activity) {    if (activity != null && activityStack.contains(activity)) {      activityStack.remove(activity);    }  }  /**   * 結束指定類名的Activity   */  public void finishActivity(Class<?> cls) {    for (Activity activity : activityStack) {      if (activity.getClass().equals(cls)) {        finishActivity(activity);        break;      }    }  }  /**   * 結束所有Activity   */  public void finishAllActivity() {    for (int i = 0, size = activityStack.size(); i < size; i++) {      if (null != activityStack.get(i)) {        finishActivity(activityStack.get(i));      }    }    activityStack.clear();  }  /**   * 退出應用程序   */  public void AppExit() {    try {      finishAllActivity();      // System.exit(0);    } catch (Exception e) {    }  }}