仅在第二次导航到 Fragment 时导致 java.IllegalStateException 错误，No Activ

问题描述

我遇到了一个非常令人费解的错误，我什至不知道如何开始解决.

I am getting a very puzzling bug that I have no idea how to even begin working through.

我有一个带有一个活动的简单应用程序，视图是用片段实现的.其中一个片段内部有一个 ViewPager；所以我决定我想使用 v4 支持库的 getChildFragmentManager 类.我还必须使用 ActionBarSherlock，这会导致问题，因为它没有随 v4 库的 v11 一起提供.

I have a simple app with one activity, the views are implemented with Fragments. One of the fragments has a ViewPager inside of it; so I decided I that I wanted to use the getChildFragmentManager class of the v4 support library. I also had to use ActionBarSherlock, which caused a problem, because it does not ship with the v11 of the v4 library.

我通过将 ABS 中的 v4 支持库替换为 v11 库来解决此问题，并且所有内容都已编译并似乎可以正常工作，包括 ViewPager.

I fixed this by replacing the v4 support library in ABS with the v11 library, and everything compiled and appeared to be working, including the ViewPager.

这是奇怪的部分:

第一次打开带有 ViewPager 的 Fragment，它可以正常工作；但是第二次导航到，应用程序崩溃，给出一个无用的堆栈跟踪.通过调试，我发现问题出在 getChildFragmentManager 返回的 FragmentManager 上；它抛出无活动错误.

The first time the fragment with the ViewPager opens, it works properly; but the SECOND time it is navigated to, the app crashes, giving a useless stack trace. From debugging, I discovered that the problem was with the FragmentManager returned by getChildFragmentManager; it throws the No Activity error.

有人知道是什么原因造成的吗?

Does anybody have any idea what could be causing this?

我将发布您认为相关的代码.

I will post code that you think is relevant.

谢谢你，大卫

推荐答案

我点击了 jeremyvillalobos answer 中的链接(其中非常有帮助)这导致我这个解决方法.

I followed the link in jeremyvillalobos answer (which was very helpful) that led me to this workaround.

public class CustomFragment extends Fragment {
    private static final Field sChildFragmentManagerField;

    static {
        Field f = null;
        try {
            f = Fragment.class.getDeclaredField("mChildFragmentManager");
            f.setAccessible(true);
        } catch (NoSuchFieldException e) {
            Log.e(LOGTAG, "Error getting mChildFragmentManager field", e);
        }
        sChildFragmentManagerField = f;
    }

    @Override
    public void onDetach() {
        super.onDetach();

        if (sChildFragmentManagerField != null) {
            try {
                sChildFragmentManagerField.set(this, null);
            } catch (Exception e) {
                Log.e(LOGTAG, "Error setting mChildFragmentManager field", e);
            }
        }
    }

    ...
}

它对我很有效，无需重新实例化片段.

It works for me well, without the need to reinstantiate the fragment.

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