Android Fragment生命周期随方向变化而变化

使用兼容性包以Fragments为目标2.2。

重新编码活动以在应用程序中使用片段后，我无法进行方向更改/状态管理，因此我创建了一个具有单个FragmentActivity和单个Fragment的小型测试应用程序。

来自方向更改的日志很奇怪，有多个对片段OnCreateView的调用。

我显然丢失了一些东西-例如分离片段并重新附加它，而不是创建新实例，但是我看不到任何文档来表明我要去哪里。

任何人都可以告诉我我在做什么错。谢谢

方向更改后，日志如下。

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）

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();
}

和碎片

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());
}

表现

<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>

您正在将片段一个接一个地分层。

发生配置更改时，旧的Fragment在重新创建时会将其自身添加到新的Activity中。在大多数情况下，这是后方的巨大痛苦。

您可以通过使用相同的片段而不是重新创建一个片段来阻止发生的错误。只需添加以下代码：

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
}

不过请注意：如果尝试从Fragment内部访问“活动视图”，则会发生问题，因为生命周期会微妙地改变。（从片段获取父活动的视图并不容易）。

引用这本书，“为了确保一致的用户体验，当由于配置更改而重新启动Activity时，Android会保留Fragment布局和相关的后向堆栈。” （第124页）

解决该问题的方法是，首先检查Fragment back堆栈是否已被填充，然后仅在尚未填充时才创建新的片段实例：

@Override
public void onCreate(Bundle savedInstanceState) {

        ...    

    FragmentOne fragment = (FragmentOne) mFragmentManager.findFragmentById(R.id.fragment_container); 

    if (fragment == null) {
        FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragment_container, new FragmentOne());
        fragmentTransaction.commit();
    }
}

如您所见，在方向更改后将调用活动的onCreate（）方法。因此，请勿在活动方向更改后执行添加片段的FragmentTransaction。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState==null) {
        //do your stuff
    }
}

片段应该并且必须保持不变。

您可以@Override使用FragmentActivity onSaveInstanceState()。请确保不要super.onSaveInstanceState()在方法中调用。

我们应该始终尝试防止nullpointer异常，因此我们必须首先在saveinstance方法中检查分发包信息。有关简短说明，请查看此博客链接

public static class DetailsActivity extends Activity {

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

        if (getResources().getConfiguration().orientation
            == Configuration.ORIENTATION_LANDSCAPE) {
            // If the screen is now in landscape mode, we can show the
            // dialog in-line with the list so we don't need this activity.
            finish();
            return;
        }

        if (savedInstanceState == null) {
            // During initial setup, plug in the details fragment.
            DetailsFragment details = new DetailsFragment();
            details.setArguments(getIntent().getExtras());
            getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
        }
    } 
}

更改配置后，框架将为您创建该片段的新实例并将其添加到活动中。所以代替这个：

FragmentOne fragment = new FragmentOne();

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

做这个：

if (mFragmentManager.findFragmentByTag(FRAG1_TAG) == null) {
    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment, FRAG1_TAG);
}

请注意，除非您调用setRetainInstance（true），否则该框架会在方向更改时添加一个FragmentOne的新实例，在这种情况下，它将添加FragmentOne的旧实例。

如果您只是做一个项目，那么项目经理说您需要实现屏幕切换功能，但是您不想屏幕切换加载不同的布局（可以创建布局和布局端口系统。

您将自动确定屏幕状态，加载相应的布局），由于需要重新初始化活动或片段，用户体验不好，不能直接在屏幕上切换，我指的是？Url = YgNfP-vHy-Nuldi7YHTfNet3AtLdN-w__O3z1wLOnzr3wDjYo7X7PYdNyhw8R24ZE22xiKnydni7R0r35s2fOLcHOiLGYT9Qh_fjqtytJki＆wd = eqa0001 = 25924

前提是您的布局使用权重的方式来布局layout_weight，如下所示：

<LinearLayout
Android:id= "@+id/toplayout"
Android:layout_width= "match_parent"
Android:layout_height= "match_parent"
Android:layout_weight= "2"
Android:orientation= "horizontal" >

所以我的方法是，在屏幕切换时，不需要加载视图文件的新布局，而是在onConfigurationChanged动态权重中修改布局，请执行以下步骤：1首先设置：在Activity属性中设置AndroidManifest.xml：android：configChanges =“ keyboardHidden | orientation | screenSize”为防止屏幕切换，请避免重新加载，以便能够在onConfigurationChanged 2中监视onConfigurationChanged方法中的重写活动或片段。

@Override
Public void onConfigurationChanged (Configuration newConfig) {
    Super.onConfigurationChanged (newConfig);
    SetContentView (R.layout.activity_main);
    if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
        //On the layout / / weight adjustment
        LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
        LinearLayout.LayoutParams LP = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
        Toplayout.setLayoutParams (LP);
        LinearLayout tradespace_layout = (LinearLayout) findViewById(R.id.tradespace_layout);
        LinearLayout.LayoutParams LP3 = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
        Tradespace_layout.setLayoutParams (LP3);
    }
    else if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT)
    {
        //On the layout / / weight adjustment
        LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
        LinearLayout.LayoutParams LP = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
        Toplayout.setLayoutParams (LP);
        LinearLayout tradespace_layout = (LinearLayout) findViewById (R.id.tradespace_layout);
        LinearLayout.LayoutParams LP3 = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
        Tradespace_layout.setLayoutParams (LP3);
    }
}