Android Fragment 生命周期超过方向变化 [英] Android Fragment lifecycle over orientation changes

问题描述

使用兼容包以使用 Fragment 来定位 2.2.

Using the compatibility package to target 2.2 using Fragments.

重新编码活动以在应用程序中使用片段后，我无法使方向更改/状态管理正常工作，因此我创建了一个包含单个 FragmentActivity 和单个 Fragment 的小型测试应用程序.

After recoding an activity to use fragments in an app I could not get the orientation changes/state management working so I've created a small test app with a single FragmentActivity and a single Fragment.

方向变化的日志很奇怪，多次调用 OnCreateView 片段.

The logs from the orientation changes are weird, with multiple calls to the fragments OnCreateView.

我显然遗漏了一些东西 - 比如分离片段并重新附加它而不是创建一个新实例，但我看不到任何说明我哪里出错的文档.

I'm obviously missing something - like detatching the fragment and reattaching it rather than creating a new instance, but I can't see any documentation which would indicate where I'm going wrong.

谁能解释一下我在这里做错了什么.谢谢

Can anyone shed some light on what I'm doing wrong here please. Thanks

方向改变后的日志如下.

The log is as follows after orientation changes.

Initial creation
12-04 11:57:15.808: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:57:15.945: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:16.081: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null


Orientation Change 1
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:57:39.031: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:39.167: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null


Orientation Change 2
12-04 11:58:32.162: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:58:32.162: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:58:32.361: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:58:32.498: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.498: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null

主要活动(FragmentActivity)

Main Activity (FragmentActivity)

public class FragmentTestActivity extends FragmentActivity {
/** Called when the activity is first created. */

private static final String TAG = "FragmentTest.FragmentTestActivity";


FragmentManager mFragmentManager;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Log.d(TAG, "onCreate");

    mFragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

    FragmentOne fragment = new FragmentOne();

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

和片段

public class FragmentOne extends Fragment {

private static final String TAG = "FragmentTest.FragmentOne";

EditText mEditText;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    Log.d(TAG, "OnCreateView");

    View v = inflater.inflate(R.layout.fragmentonelayout, container, false);

    // Retrieve the text editor, and restore the last saved state if needed.
    mEditText = (EditText)v.findViewById(R.id.editText1);

    if (savedInstanceState != null) {

        Log.d(TAG, "OnCreateView->SavedInstanceState not null");

        mEditText.setText(savedInstanceState.getCharSequence("text"));
    }
    else {
        Log.d(TAG,"OnCreateView->SavedInstanceState null");
    }
    return v;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    Log.d(TAG, "FragmentOne.onSaveInstanceState");

    // Remember the current text, to restore if we later restart.
    outState.putCharSequence("text", mEditText.getText());
}

清单

<uses-sdk android:minSdkVersion="8" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:label="@string/app_name"
        android:name=".activities.FragmentTestActivity" 
        android:configChanges="orientation">
        <intent-filter >
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

推荐答案

您将 Fragment 一层一层地叠加在一起.

You're layering your Fragments one on top of the other.

当发生配置更改时，旧 Fragment 会在重新创建时将其自身添加到新 Activity.大多数时候，这是背部巨大的疼痛.

When a config change occurs the old Fragment adds itself to the new Activity when it's recreated. This is a massive pain in the rear most of the time.

您可以通过使用相同的 Fragment 而不是重新创建一个新的 Fragment 来阻止错误的发生.只需添加此代码:

You can stop errors occurring by using the same Fragment rather than recreating a new one. Simply add this code:

if (savedInstanceState == null) {
    // only create fragment if activity is started for the first time
    mFragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment);
    fragmentTransaction.commit();
} else {        
    // do nothing - fragment is recreated automatically
}

但请注意:如果您尝试从 Fragment 内部访问活动视图，则会出现问题，因为生命周期会发生微妙的变化.(从 Fragment 的父 Activity 获取视图并不容易).

Be warned though: problems will occur if you try and access Activity Views from inside the Fragment as the lifecycles will subtly change. (Getting Views from a parent Activity from a Fragment isn't easy).

这篇关于Android Fragment 生命周期超过方向变化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！