如何在Android应用中实现一个返回键功能

  /**
   * 返回键处理
   */
  @Override
  public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode==KeyEvent.KEYCODE_BACK){
      boolean result=MiddleManager.getInstance().goBack();
      if(!result){
        Toast.makeText(MainActivity.this, "是否退出应用", 1).show();
      }
      return false;
    }
    return super.onKeyDown(keyCode, event);
  }

  //操作历史栈
  private LinkedList<String> HISTORY=new LinkedList<String>();
  /**
   * 处理返回键
   * @return 
   */
  public boolean goBack() {
    //如果为空会抛异常
    if(HISTORY.size()>0){
      if(HISTORY.size()==1){
        return false;
      }
      
      HISTORY.removeFirst();
      if(HISTORY.size()>0){
        String key=HISTORY.getFirst();
        BaseView targetView=VIEWCACHE.get(key);
        mainContainer.removeAllViews();
        View child=targetView.getView();
        mainContainer.addView(child);
        child.startAnimation(AnimationUtils.loadAnimation(mainContainer.getContext(), R.anim.left_to_right));
        currentView=targetView;
        return true;
      }
    }
    return false;
  }

  /**
   * 加载界面
   */
  public void loadView(Class<&#63; extends BaseView> baseViewClass) {
    BaseView baseView=null;
    //判断是否存在
    String key=baseViewClass.getSimpleName();
    if(VIEWCACHE.containsKey(key)){
      baseView=VIEWCACHE.get(key);
    }else{
      try {
        Constructor<&#63; extends BaseView> constructor;
        constructor = baseViewClass.getConstructor(Context.class);
        baseView=constructor.newInstance(mainContainer.getContext());
      } catch (Exception e) {
        e.printStackTrace();
      }
      VIEWCACHE.put(key, baseView);
    }
    mainContainer.removeAllViews();
    View child=baseView.getView();
    mainContainer.addView(child);
    child.startAnimation(AnimationUtils.loadAnimation(mainContainer.getContext(), R.anim.left_to_right));
    currentView=baseView;
    //放入栈
    HISTORY.addFirst(key);
  }