Android，如何保存Fragment的状态

Stack Overflow对此问题的讨论这里

Save state in fragment

在Fragment里面，利用onSaveInstanceState保存数据，并可在onActivityCreated里面恢复数据。

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    ...
    if (savedInstanceState != null) {
        // Restore the fragment's state here
    }
}

public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    // Save the fragment's state here
}

Save state in Activity

接下来重点是，在Activity里面，利用onSaveInstanceState保存Fragment实例的数据，并可在onCreate里面恢复数据。

private Fragment myFragment;

public void onCreate(Bundle savedInstanceState) {
    ...
    if (savedInstanceState == null) {
        // Instantiate fragment
    } else {
        // Restore the fragment's instance
        myFragment = getSupportFragmentManager().getFragment(
                    savedInstanceState, "fragment");
    }
    ...
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    //Save the fragment's instance
    // fragment instance may be null
    if (myFragment != null) {
        getSupportFragmentManager().putFragment(outState, "fragment", myFragment);
    }
}

End

最后，不要忽略状态保存的问题，在内存不足或者系统限制比较苛刻的机器上面，都有可能出现Fragment或Activity被回收，比如经常出现拍照之后返回App，但App里面的数据被清空了，更常见的就是旋转屏幕，所以要保存好自己需要的数据。

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