Question

我有一个Activity，可在ActionBar中加载2个标签。标签1加载Fragment，这将使WebView膨胀，而标签2加载带有地图的Fragment。最初，我遇到了更改标签导致应用程序崩溃的问题。我按照说明here执行了onDestroyView()。

现在的问题是，如果我按Tab 1（WebView）的后退按钮，它会正确退出Activity。但如果我在Tab 2（地图）上这样做，应用程序崩溃了。当我改变方向时，完全相同的情况适用。我确信它与onDestroyView()有关，但我不确定它是什么。

我甚至试图Override后退按钮，但没有任何作用。

这是我提供一些上下文的代码：

活动类：

public class MyActivity extends Activity {

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

    //Displaying the tabs by calling ActionBar
    ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    //Details Tab
    String label1 = getResources().getString(R.string.details);
    Tab tab = actionBar.newTab();
    tab.setText(label1);
    TabListener<DetailsFragment> t1 = new TabListener<DetailsFragment>(this, label1, DetailsFragment.class);
    tab.setTabListener(t1);
    actionBar.addTab(tab);

    //Map Tab
    String label2 = getResources().getString(R.string.map);
    tab = actionBar.newTab();
    tab.setText(label2);
    TabListener<MapFragment> t2 = new TabListener<MapFragment>(this, label2, MapFragment.class);
    tab.setTabListener(t2);
    actionBar.addTab(tab);
}

private class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    /**
     * Constructor used each time a new tab is created.
     * 
     * @param activity
     *            The host Activity, used to instantiate the fragment
     * @param tag
     *            The identifier tag for the fragment
     * @param clz
     *            The fragment's Class, used to instantiate the fragment
     */
    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);

        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            // Detach the fragment, because another one is being attached
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // User selected the already selected tab. Usually do nothing.
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
} }

DetailsFragment：

public class DetailsFragment extends Fragment {


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

    View v = inflater.inflate(R.layout.morning, container, false);
    WebView webview = (WebView) v.findViewById(R.id.details);
    webview.loadUrl("file:///android_asset/pools/details.html");
    return v;
} }

MapFragment：

public class MapFragment extends Fragment {

static final LatLng mapLatLng = new LatLng("some numbers", "some numbers");
private GoogleMap map;

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

    View v = inflater.inflate(R.layout.map, container, false);
    map = ((MapFragment)getFragmentManager().findFragmentById(R.id.map)).getMap();
    Marker amksc = map.addMarker(new MarkerOptions().position(mapLatLng).title("Map"));

    map.moveCamera(CameraUpdateFactory.newLatLngZoom(mapLatLng, 18)); 
    return v;
}


@Override
public void onDestroyView() {
    super.onDestroyView();
    MapFragment destroyMe = (MapFragment)getFragmentManager().findFragmentById(R.id.map);
    if (destroyMe != null) {
        getFragmentManager().beginTransaction().remove(destroyMe).commit();
    }
} }

感谢您阅读这么长的帖子。任何帮助是极大的赞赏。没有笔记本电脑我会离开一段时间（确切地说是15天），所以我可能无法回答并测试你的答案，但请放心，我会=）

提前致谢！

已编辑以包含错误日志（不确定如何格式化）

04-25 11:27:54.333: E/AndroidRuntime(21779): FATAL EXCEPTION: main

04-25 11:27:54.333: E/AndroidRuntime(21779): java.lang.NullPointerException

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1380)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:430)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Handler.handleCallback(Handler.java:615)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Handler.dispatchMessage(Handler.java:92)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Looper.loop(Looper.java:213)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.ActivityThread.main(ActivityThread.java:4786)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at java.lang.reflect.Method.invokeNative(Native Method)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at java.lang.reflect.Method.invoke(Method.java:511)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

我似乎已经解决了后退按钮和方向更改问题。

这里的技巧是不使用onDestroyView()，而是改变处理片段的方式。而不是ft.attach(mFragment)和ft.detach(mFragment)，我将其更改为ft.show(mFragment)和ft.hide(mFragment)。

至于导致应用程序崩溃的方向更改，我相信（如果我错了，请纠正我），只要您没有其他横向布局，就可以将android:configChanges="orientation|screenSize"添加到清单中这个活动，像这样：

<activity 
        android:theme="@style/AppTheme" 
        android:name="MyFragmentActivity" 
        android:label="@string/fragmentActivity" 
        android:configChanges="orientation|screenSize">
    </activity>

Answer 2

GoogleMap需要一点时间加载，因此如果您想使用它，它可能会返回null。尝试在MapFragment的onActivityCreated（）方法中移动此代码

map = ((MapFragment)getFragmentManager().findFragmentById(R.id.map)).getMap();
Marker amksc = map.addMarker(new MarkerOptions().position(mapLatLng).title("Map"));

map.moveCamera(CameraUpdateFactory.newLatLngZoom(mapLatLng, 18));

那曾经适合我。请务必查看Fragment Lifecycle

Answer 3

这对我有用..试试吧下面的代码在onDestroy（）方法中写入

@Override
    public void onDestroy() { 
if (fragment != null
                        && getFragmentManager().findFragmentById(
                                fragment.getId()) != null) {

                    getFragmentManager().beginTransaction().remove(fragment)
                            .commit();
                    fragment = null;
                }
}

当按下后退按钮或方向发生变化时，带有地图的片段会崩溃应用程序

3 个答案: