活动和片段生命周期和方向变化

Question

我一直有非常奇怪的问题Fragments和方向更改已导致强制关闭而不遵循逻辑模式。

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

以下是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();
    }
}

TestFragment

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（启动Activity ，附加Fragment ，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文档会说：

当发生这样的更改时，Android会重新启动正在运行的Activity（调用onDestroy（），然后调用onCreate（））

这表明它应该关闭Activity及其内容，如生命周期建议（并且它确实）但是然后通过相同的有序流程重新创建新方向的Activity 。 这不会发生，似乎尝试重新创建Fragment ， 然后在活动重新创建中创建一个新Fragment 。

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？ 为什么Fragment引用被保留并重新创建时，它应该是该Activity一部分，据说它被完全破坏并重新创建？ 我可以证明Fragment故意将其与活动分开。 但导致这些问题的原因是为什么原始Fragment在Activity 之前附加并重新创建？ 它似乎并不遵循Android进程其余部分所遵循的逻辑生命周期。

Answer 1

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

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

您可能要检查的源代码在这里 ，并在这里更好地理解这种行为。

Answer 2

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activity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();
}

当发生配置更改时，旧的Fragment不会被销毁 - 它会在重新创建时将其自身添加回Activity。