工具栏（SupportActionBar）标题在方向更改时更改为应用程序名称

Question

我在活动中有以下代码：

protected void onCreate(Bundle savedInstanceState) {
    ...
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    ActionBar actionBar = getSupportActionBar();
    if (actionBar != null) {
      actionBar.setDisplayHomeAsUpEnabled(true);
    }
    ...
}

我正在从onresume()中的不同片段更新ActionBar标题，如下所示：

ActionBar actionBar = ((AppCompatActivity) getActivity()).getSupportActionBar();
if (actionBar != null) {
    actionBar.setTitle(title);
}

final ActionBar actionBar = ((AppCompatActivity)getActivity()).getSupportActionBar();
if (actionBar != null) {
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            Log.d("SWAPNIL", "IN RUN BEFORE: " + actionBar.getTitle());
            actionBar.setTitle(title);
            Log.d("SWAPNIL", "IN RUN AFTER : " + actionBar.getTitle());
        }
    }, 3000);
}

10-13 10:27:04.526 3719-3719/com.example.xxxx D/SWAPNIL: onResumeHelp
10-13 10:27:07.528 3719-3719/com.example.xxxx D/SWAPNIL: IN RUN BEFORE: MY APP NAME
10-13 10:27:07.528 3719-3719/com.example.xxxx D/SWAPNIL: IN RUN AFTER : title
10-13 10:27:21.012 3719-3719/com.example.xxxx D/SWAPNIL: onResumeHelp
10-13 10:27:24.013 3719-3719/com.example.xxxx D/SWAPNIL: IN RUN BEFORE: title
10-13 10:27:24.013 3719-3719/com.example.xxxx D/SWAPNIL: IN RUN AFTER : title

Answer 1

好吧，最后，在花了两天时间在这个愚蠢的事情上，我得到了解决方案（我会说变通）。

这可能是嵌套的片段错误。

我有嵌套片段结构。正如我们所知，fragment.getactivity()返回父级activity。经过大量调试后，我注意到如果在方向改变后调用getactivity()(fragment.onactivitycreate())，它会返回旧的活动的引用，除非在最上层的父片段中正确地返回新创建的活动。

因此，我编写了这个方法来从任何片段获取当前活动:

/**
 * When inside a nested fragment and Activity gets recreated due to reasons like orientation
 * change, {@link android.support.v4.app.Fragment#getActivity()} returns old Activity but the top
 * level parent fragment's {@link android.support.v4.app.Fragment#getActivity()} returns current,
 * recreated Activity. Hence use this method in nested fragments instead of
 * android.support.v4.app.Fragment#getActivity()
 *
 * @param fragment
 *  The current nested Fragment
 *
 * @return current Activity that fragment is hosted in
 */
public Activity getActivity(Fragment fragment) {
    if (fragment == null) {
        return null;
    }
    while (fragment.getParentFragment() != null) {
        fragment = fragment.getParentFragment();
    }
    return fragment.getActivity();
}