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我一直遇到非常奇怪的问题Fragments和方向变化，这些问题导致强制关闭并且不遵循逻辑模式。

我创建了一个简单的Activity生命周期调试应用程序，它通过向 logcat 报告调用来Fragment简单地实现Activity 生命周期和Fragment 生命周期的每一步。

这是TestActivity和TestFragment类：

测试活动

public class TestActivity extends Activity {
    Context ct = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Log.e("ACT", "onCreate called");

        ct = getApplicationContext();

        FrameLayout fl = new FrameLayout(ct);
        fl.setId(1000);

        TestFragment tf = new TestFragment();
        getFragmentManager().beginTransaction().add(fl.getId(), tf, "").commit();

        setContentView(fl);
    }

    @Override
    protected void onStart() {
        Log.e("ACT", "onStart called");
        super.onStart();
    }

    @Override
    protected void onResume() {
        Log.e("ACT", "onResume called");
        super.onResume();
    }

    @Override
    protected void onPause() {
        Log.e("ACT", "onPause called");
        super.onPause();
    }

    @Override
    protected void onStop() {
        Log.e("ACT", "onStop called");
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        Log.e("ACT", "onDestroy called");
        super.onDestroy();
    }

    @Override
    protected void onRestart() {
        Log.e("ACT", "onRestart called");
        super.onRestart();
    }
}

测试片段

public class TestFragment extends Fragment {
    Context ctFrag = null;

    @Override
    public void onAttach(Activity activity) {
        Log.e("FRAG", "onAttach called");
        super.onAttach(activity);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Log.e("FRAG", "onCreate called");

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.e("FRAG", "onCreateView called");

        ctFrag = ((TestActivity) getActivity()).ct;

        TextView tv = new TextView(ctFrag);
        tv.setText("My test TextView");

        return tv;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        Log.e("FRAG", "onActivityCreated called");
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onStart() {
        Log.e("FRAG", "onStart called");
        super.onStart();
    }

    @Override
    public void onResume() {
        Log.e("FRAG", "onResume called");
        super.onResume();
    }

    @Override
    public void onPause() {
        Log.e("FRAG", "onPause called");
        super.onPause();
    }

    @Override
    public void onStop() {
        Log.e("FRAG", "onStop called");
        super.onStop();
    }

    @Override
    public void onDestroyView() {
        Log.e("FRAG", "onDestroyView called");
        super.onDestroyView();
    }

    @Override
    public void onDestroy() {
        Log.e("FRAG", "onDestroy called");
        super.onDestroy();
    }

    @Override
    public void onDetach() {
        Log.e("FRAG", "onDetach called");
        super.onDetach();
    }
}

初始化时，Logcat 输出遵循预期的顺序（开始Activity、Fragment连接时、其生命周期调用发生等）：

01-29 10:12:50.270: E/ACT(3321): onCreate called
01-29 10:12:50.760: E/FRAG(3321): onAttach called
01-29 10:12:50.760: E/FRAG(3321): onCreate called
01-29 10:12:50.760: E/FRAG(3321): onCreateView called
01-29 10:12:50.770: E/FRAG(3321): onActivityCreated called
01-29 10:12:50.770: E/ACT(3321): onStart called
01-29 10:12:50.770: E/FRAG(3321): onStart called
01-29 10:12:50.770: E/ACT(3321): onResume called
01-29 10:12:50.770: E/FRAG(3321): onResume called

但问题是，当方向发生变化时，Android 文档说：

当发生这样的变化时，Android会重启正在运行的Activity（onDestroy()被调用，然后是onCreate()）

这表明它应该像生命周期所建议的那样关闭Activity其及其内容（并且确实如此），但然后通过相同的有序过程Activity以新的方向重新创建。这不会发生，似乎Fragment试图重新创建，然后在活动重新创建中创建一个新的。

01-29 10:17:52.249: E/FRAG(3321): onPause called
01-29 10:17:52.259: E/ACT(3321): onPause called
01-29 10:17:52.269: E/FRAG(3321): onStop called
01-29 10:17:52.269: E/ACT(3321): onStop called
01-29 10:17:52.279: E/FRAG(3321): onDestroyView called
01-29 10:17:52.299: E/FRAG(3321): onDestroy called
01-29 10:17:52.299: E/FRAG(3321): onDetach called
01-29 10:17:52.299: E/ACT(3321): onDestroy called
01-29 10:17:52.650: E/FRAG(3321): onAttach called
01-29 10:17:52.650: E/FRAG(3321): onCreate called
01-29 10:17:52.650: E/ACT(3321): onCreate called
01-29 10:17:53.020: E/FRAG(3321): onCreateView called
01-29 10:17:53.020: E/FRAG(3321): onActivityCreated called
01-29 10:17:53.030: E/FRAG(3321): onAttach called
01-29 10:17:53.030: E/FRAG(3321): onCreate called
01-29 10:17:53.030: E/FRAG(3321): onCreateView called
01-29 10:17:53.030: E/FRAG(3321): onActivityCreated called
01-29 10:17:53.060: E/ACT(3321): onStart called
01-29 10:17:53.060: E/FRAG(3321): onStart called
01-29 10:17:53.060: E/FRAG(3321): onStart called
01-29 10:17:53.060: E/ACT(3321): onResume called
01-29 10:17:53.060: E/FRAG(3321): onResume called
01-29 10:17:53.060: E/FRAG(3321): onResume called

显然有很多解决方案可以解决这个问题，但我的问题是为什么会发生这种情况？当引用应该是应该完全销毁和重新创建的引用的一部分时，为什么要Fragment维护和重新创建引用？我可以通过故意与活动分开来证明这一点。但是导致问题的原因是，为什么要在原件之前附加并重新创建原件？它似乎没有遵循 Android 进程的其余部分所做的逻辑生命周期。ActivityFragmentFragmentActivity

4

2 回答 2

10

onSaveInstanceState(Bundle)发生这种情况是因为活动在被销毁之前调用。默认情况下，活动在此方法中保存其片段的状态。

稍后，当重新创建活动时，在活动方法中重新创建旧片段onCreate(Bundle savedInstanceState)。

您可能需要在此处和此处查看源代码以更好地理解此行为。

于 2013-01-30T10:04:41.823 回答
1

这是因为您在重新创建活动时一次又一次地添加片段。您可以在活动的 onCreate 方法中使用以下代码来避免重新创建片段：

if(savedInstanceState == null) 
{
    mFragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment);
    fragmentTransaction.commit();
}

当配置更改发生时，旧的 Fragment 不会被销毁——它会在重新创建时将自身添加回 Activity。

于 2015-12-01T09:26:32.723 回答