实现activity管理器一次退出所有activity

private static MyActivityManager instance;
private Stack activityStack;//activity栈

private MyActivityManager() {
}
//单例模式
public static MyActivityManager getInstance() {
    if (instance == null) {
        instance = new MyActivityManager();
    }
    return instance;
}
//把一个activity压入栈中
public void pushOneActivity(Activity actvity) {
    if (activityStack == null) {
        activityStack = new Stack();
    }
    activityStack.add(actvity);
    Log.d("MyActivityManager ", "size = " + activityStack.size());
}
//获取栈顶的activity，先进后出原则
public Activity getLastActivity() {
    return activityStack.lastElement();
}
//移除一个activity
public void popOneActivity(Activity activity) {
    if (activityStack != null && activityStack.size() > 0) {
        if (activity != null) {
            activity.finish();
            activityStack.remove(activity);
            activity = null;
        }

    }
}
//退出所有activity
public void finishAllActivity() {
    if (activityStack != null) {
        while (activityStack.size() > 0) {
            Activity activity = getLastActivity();
            if (activity == null) break;
            popOneActivity(activity);
        }
    }
}}