Android开发案例 - 注册登录

本文只涉及UI方面的内容, 如果您是希望了解非UI方面的访客, 请跳过此文. 在微博, 微信等App的注册登录过程中有这样的交互场景(如下图):

1. 打开登录界面
2. 在登录界面中, 点击注册, 跳转到注册界面
3. 如果取消注册, 则回退到登录界面, 如果完成注册,跳转到主页面

在整个交互场景里有个问题, 就是如何在完成注册之后关闭之前已经打开过的界面. 那如果层级更深的话, 应该如何处理?

 

注: 按此文分割线以下的方式处理, 存在一些问题, 如下:
> 假设注册登录之前的界面是欢迎界面, 并注册登录成功
> 这时, 以Intent.FLAG_ACTIVITY_CLEAR_TASK & Intent.FLAG_ACTIVITY_NEW_TASK方式启动主界面
> 进入应用管理强制停止应用, 再从最近使用过应用的列表进入应用
> 这时, 问题就来了, 应用没有进入欢迎界面, 而是直接进入了主界面

建议使用Intent.FLAG_ACTIVITY_CLEAR_TOP来实现注册登录的界面跳转, 大体思路, 如下:
> 设置欢迎界面的activity.launchMode属性为singleTop, 并接管onNewIntent(Intent), 若满足跳转主界面的条件, 则直接进入主界面
> 注册登录成功后, 使用Intent.FLAG_ACTIVITY_CLEAR_TOP方式跳转到欢迎界面
> 这时, 程序会运行到欢迎界面的onNewIntent(Intent), 这是因为欢迎界面现在是BackStack的栈顶activity了. 最后将直接进入主界面

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知识要点

• Intent.FLAG_ACTIVITY_CLEAR_TASK
• Intent.FLAG_ACTIVITY_NEW_TASK

P.S. Intent.FLAG_ACTIVITY_CLEAR_TASK与 Intent.FLAG_ACTIVITY_CLEAR_TOP不同, 它是在API-Level-11时引入的, 使用它会清空当前task, 并让新activity成为一个空task的root activity, 另外它要求与Intent.FLAG_ACTIVITY_NEW_TASK一起使用. 而Intent.FLAG_ACTIVITY_CLEAR_TOP的调用效果同activity的singTask启动模式.

　　官方文档如下:

public static final int FLAG_ACTIVITY_CLEAR_TASK

Added in API level 11

If set in an Intent passed to Context.startActivity(), this flag will cause any existing task that would be associated with the activity to be cleared before the activity is started. That is, the activity becomes the new root of an otherwise empty task, and any old activities are finished. This can only be used in conjunction with FLAG_ACTIVITY_NEW_TASK.

public static final int FLAG_ACTIVITY_NEW_TASK

Added in API level 1

If set, this activity will become the start of a new task on this history stack. A task (from the activity that started it to the next task activity) defines an atomic group of activities that the user can move to. Tasks can be moved to the foreground and background; all of the activities inside of a particular task always remain in the same order. See Tasks and Back Stack for more information about tasks.

This flag is generally used by activities that want to present a "launcher" style behavior: they give the user a list of separate things that can be done, which otherwise run completely independently of the activity launching them.

When using this flag, if a task is already running for the activity you are now starting, then a new activity will not be started; instead, the current task will simply be brought to the front of the screen with the state it was last in. See FLAG_ACTIVITY_MULTIPLE_TASK for a flag to disable this behavior.

This flag can not be used when the caller is requesting a result from the activity being launched.

实现代码

> 定义

• LoginActivity - 登录界面
• RegisterActivity - 注册界面
• MainActivity - 主界面

> LoginActivity.java

略. 常规代码实现, 即直接调用startActivity来启动注册界面, 因此, 在注册界面按回退键后, 还是会回到该界面.

> RegisterActivity.java

import ...

public class RegisterActivity extends Activity {
    ...

    /**
     * 注册成功, 跳转到主界面
     */
    private void finishWhenRegisterSucceeded() {
        ComponentName component = new ComponentName(this, MainActivity.class);
        Intent intent = IntentCompat.makeRestartActivityTask(component);
        startActivity(intent);
    }
}

在上述代码中, 使用了android-support-v4中的IntentCompat类, 该类封装了上述两个Intent-Flag.

到这里, 注册成功后, 进入了MainActivity后, MainActivity就是一个新task的root activity了, 而其他activity则都被清理了. 需要说明的是, finishWhenRegisterSucceeded() 没有对启动RegisterActivity的LoginActivity做任何处理或者Intent回传.

END.