Question

我有一个抽象基类，用于实例化一个片段的活动：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
         android:id="@+id/fragmentContainer" android:layout_width="match_parent" android:layout_height="match_parent" >
</FrameLayout>


public abstract class SingleFragmentActivity extends Activity {
    protected abstract Fragment createFragment();

    private Fragment m_fragment;
    public Fragment getSingleFragment() { return m_fragment; }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment);

        FragmentManager fm = getFragmentManager();
        m_fragment = fm.findFragmentById( R.id.fragmentContainer );
        Log.d("SingleFragment", "fetching a fragment");
        if ( m_fragment == null ) {
            Log.d("SingleFragment", "SingleFragment requires creating a new one");
            m_fragment = createFragment();
            fm.beginTransaction().add( R.id.fragmentContainer, m_fragment ).commit();
        } else {
            Log.d("SingleFragment", "SingleFragment reusing one from fragment manager");
        }
    }
}

...加上一个简单的活动和片段：

public class LoginActivity extends SingleFragmentActivity {
    private static final String TAG = "LOGIN ACTIVITY";

    private LoginFragment m_loginFragment;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.d(TAG,"onCreate");
        super.onCreate(savedInstanceState);

        m_loginFragment = (LoginFragment) getSingleFragment();
        Log.d(TAG,"...login fragment foo = "+m_loginFragment.getFoo());
        m_loginFragment.setFoo( "Here's a new foo");
    }

    @Override
    public void onPause() { super.onPause(); Log.d(TAG,"onPause"); }

    @Override
    public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); }

    @Override
    public void onResume() { super.onResume(); Log.d(TAG,"onResume"); }


    @Override
    protected Fragment createFragment() {
        Log.d(TAG,"createFragment()");
        return new LoginFragment();
    }
}

public class LoginFragment extends Fragment {
    private static final String TAG = "LOGIN FRAGMENT";

    private String foo = "not set yet";
    public String getFoo() { return foo; }
    public void setFoo(String s) { foo = s; }

    @Override
    public void onCreate( Bundle savedInstanceState ) {
        super.onCreate(savedInstanceState);
        Log.d(TAG,"onCreate");
    }

    @Override
    public void onPause() { super.onPause(); Log.d(TAG,"onPause"); }

    @Override
    public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); }

    @Override
    public void onResume() { super.onResume(); Log.d(TAG,"onResume"); }
}

如果我运行此代码，并在手机启动后旋转手机，我会看到以下日志：

08-07 15:02:51.310: LOGIN ACTIVITY: onCreate
08-07 15:02:51.340: SingleFragment: fetching a fragment
08-07 15:02:51.340: SingleFragment: SingleFragment requires creating a new one
08-07 15:02:51.340: LOGIN ACTIVITY: createFragment()
08-07 15:02:51.340: LOGIN ACTIVITY: ...login fragment foo = not set yet
08-07 15:02:51.340: LOGIN FRAGMENT: onCreate
08-07 15:02:51.340: LOGIN ACTIVITY: onResume
08-07 15:02:51.340: LOGIN FRAGMENT: onResume
08-07 15:02:59.799: LOGIN FRAGMENT: onPause
08-07 15:02:59.799: LOGIN ACTIVITY: onPause
08-07 15:02:59.809: LOGIN FRAGMENT: onDestroy
08-07 15:02:59.809: LOGIN ACTIVITY: onDestroy
08-07 15:02:59.829: LOGIN ACTIVITY: onCreate
08-07 15:02:59.829: LOGIN FRAGMENT: onCreate
08-07 15:02:59.869: SingleFragment: fetching a fragment
08-07 15:02:59.869: SingleFragment: SingleFragment reusing one from fragment manager
08-07 15:02:59.869: LOGIN ACTIVITY: ...login fragment foo = not set yet
08-07 15:02:59.869: LOGIN ACTIVITY: onResume
08-07 15:02:59.869: LOGIN FRAGMENT: onResume

一切都按预期工作：旋转手机会导致活动和碎片被破坏和重建;我看到片段管理器恢复某些东西，但我的问题是“什么？”成员变量foo不会被保留，那么正在恢复的是什么？

Answer 1

我也遇到了同样的问题，有时候发布了一个问题 - After screen rotation, findFragmentById() returns a fragment, even if there's no such ID inside the layout

那时，http://developer.android.com/training/basics/fragments/creating.html的文件提到了这一点：

当配置更改导致托管这些活动时要重新启动的片段，其新实例可能会使用不同的布局不包含与先前布局相同的片段。在这 case仍然会实例化所有以前的片段在新实例中运行。但是，任何不再是与视图层次结构中的标记关联的将不具有它们内容视图已创建，将从isInLayout（）返回false。（该这里的代码还显示了如何确定片段是否放置在容器不再在具有该容器的布局中运行在这种情况下，请避免创建其视图层次结构。）

现在该部分在该文件中不存在。

如果此片段已添加到布局中，您可以查看isInLayout()。

FragmentManager保留了什么？

1 个答案: