onBackPressed导致FragmentActivity重启

原创

truesea 2013-11-26 17:04:00 ©著作权

文章标签 FragmentActivity重启 onBackPressed 文章分类 Android 移动开发

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问题：onBackPressed导致FragmentActivity重启

描述：

HomeActivity和MyTsyActivity是FragmentActivity的两个子类。

从HomeActivity跳转到MyTsyActivity很流畅，没有出现任何问题。

Intent intent = new Intent(context, MyTsyActivity.class);
startActivity(intent);

从MyTsyActivity返回到HomeActivity中有两种方法

（1）点击标题栏的返回按钮，在返回按钮的clickListener中的onClick方法中调用this.finish()

public void onClick(View v) {
    if(v==btnBack) {
        finish();
    }
}

结果是先调用HomeActivity的onStart方法，再调用MyTsyActivity的onDestroy方法。

（2）点击pad底部的返回按键，触发MyTsyActivity的onBackPressed方法

@Override
public void onBackPressed() {
    Logger.v(TAG, "@onBackPressed.");
    super.onBackPressed();
}

结果会重启HomeActivity，导致返回去比较卡，不流畅。但也不是每次都会重启。

打印出来的日志如下：

11-26 16:46:52.860: V/MyTsyActivity(32384): @onBackPressed.
11-26 16:46:53.190: V/HomeActivity(32384): @onDestroy.
11-26 16:46:53.190: V/HomeActivity(32384): @stopService.
11-26 16:46:53.200: V/MainFragment(32384): @onDestroyView
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroyView
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroy
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroyView
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroy
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroyView
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroy
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroyView
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroy
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroyView
11-26 16:46:53.200: V/HotVideoFragment(32384): @onDestroy
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroyView
11-26 16:46:53.200: V/RecommandFragment(32384): @onDestroy
11-26 16:46:53.210: V/HomeActivity(32384): @onCreate.
11-26 16:46:53.210: V/MainFragment(32384): @onCreate
11-26 16:46:53.210: V/HotVideoFragment(32384): @onCreate
11-26 16:46:53.210: V/RecommandFragment(32384): @onCreate
11-26 16:46:53.210: V/HotVideoFragment(32384): @onCreate
11-26 16:46:53.210: V/RecommandFragment(32384): @onCreate
11-26 16:46:53.210: V/HotVideoFragment(32384): @onCreate
11-26 16:46:53.210: V/RecommandFragment(32384): @onCreate
11-26 16:46:53.250: V/HomeActivity(32384): @launchService.
11-26 16:46:53.250: V/MainFragment(32384): @onCreateView
11-26 16:46:53.260: V/MainFragment(32384): @initializeView. create each fragment.
11-26 16:46:53.260: V/MainFragment(32384): @onActivityCreated. data is null. get data from network.
11-26 16:46:53.270: V/HotVideoFragment(32384): @onCreateView
11-26 16:46:53.290: V/RecommandFragment(32384): @onCreateView
11-26 16:46:53.290: V/HotVideoFragment(32384): @onCreateView

（3）如果使用onKeyDown来处理返回按键，也会出现FragmentActivity重启的问题。

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
        Logger.v(TAG, "@onKeyDown. keyCode is KeyEvent.KEYCODE_BACK");
        this.finish();
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

在onKeyDown中，如果是KEYCODE_BACK，返回true，表示不再执行onBackPressed方法。

打印出来的日志跟调用onBackPressed类似。

多尝试了几次，发现onKeyDown和onBackPressed两个方法引起Activity重启不是每次都发生。其中有一次的现象是：前4、5次都没有重启，再来一次就重启。

在FragmentActivity.onBackPressed文档说明中发现：

Take care of popping the fragment back stack or finishing the activity as appropriate.

没有明白这句话具体意思。

参考资料：

1. ANDROID API：FragmentActivity

http://developer.android.com/reference/android/support/v4/app/FragmentActivity.html