[android] 实现返回键操作思路

    /**
     * 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<? 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<? 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);
    }