java - fragment 错误中的 Android getListView()

Question

我的 Android 应用程序一直有问题，在选项卡之间滑动时它崩溃并出现以下错误:

09-16 16:19:27.142    4750-4750/com.khackett.runmate E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.khackett.runmate, PID: 4750
    java.lang.IllegalStateException: Content view not yet created
            at android.support.v4.app.ListFragment.ensureList(ListFragment.java:328)
            at android.support.v4.app.ListFragment.getListView(ListFragment.java:222)
            at com.khackett.runmate.ui.MyRunsFragment$1.done(MyRunsFragment.java:167)
            at com.khackett.runmate.ui.MyRunsFragment$1.done(MyRunsFragment.java:135)
            at com.parse.ParseTaskUtils$2$1.run(ParseTaskUtils.java:115)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

这是 MyRunsFragment:

public class MyRunsFragment extends ListFragment {

    protected SwipeRefreshLayout mSwipeRefreshLayout;

    // member variable to store the list of routes the user has accepted
    protected List<ParseObject> mAcceptedRoutes;

    private int MY_STATUS_CODE = 1111;

    // Default constructor for MyRunsFragment
    public MyRunsFragment() {
    }

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

        View rootView = inflater.inflate(R.layout.fragment_my_runs, container, false);

        // Set SwipeRefreshLayout component
        mSwipeRefreshLayout = (SwipeRefreshLayout) rootView.findViewById(R.id.swipeRefreshLayout);
        // Set the onRefreshListener
        mSwipeRefreshLayout.setOnRefreshListener(mOnRefreshListener);
        mSwipeRefreshLayout.setColorSchemeResources(
                R.color.swipeRefresh1,
                R.color.swipeRefresh2,
                R.color.swipeRefresh3,
                R.color.swipeRefresh4);

        return rootView;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        // Retrieve the accepted routes from the Parse backend
        retrieveAcceptedRoutes();
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        // create the message object which is set to the message at the current position
        ParseObject route = mAcceptedRoutes.get(position);

        // String messageType = message.getString(ParseConstants.KEY_FILE_TYPE);

        JSONArray parseList = route.getJSONArray(ParseConstants.KEY_LATLNG_POINTS);
        JSONArray parseListBounds = route.getJSONArray(ParseConstants.KEY_LATLNG_BOUNDARY_POINTS);
        String objectId = route.getObjectId();
        String routeName = route.getString(ParseConstants.KEY_ROUTE_NAME);
        // JSONArray ids = route.getJSONArray(ParseConstants.KEY_RECIPIENT_IDS);

        // Start a map activity to display the route
        Intent intent = new Intent(getActivity(), MapsActivityTrackRun.class);
        intent.putExtra("parseLatLngList", parseList.toString());
        intent.putExtra("parseLatLngBoundsList", parseListBounds.toString());
        intent.putExtra("myRunsObjectId", objectId);
        intent.putExtra("myRunsRouteName", routeName);

        // Start the MapsActivityDisplayRoute activity
        startActivityForResult(intent, MY_STATUS_CODE);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {

    }

    private void retrieveAcceptedRoutes() {
        // query the routes class/table in parse
        // get messages where the logged in user ID is in the list of the recipient ID's (we only want to retrieve the messages sent to us)
        // querying the message class is similar to how we have been querying users
        ParseQuery<ParseObject> queryRoute = new ParseQuery<ParseObject>(ParseConstants.CLASS_ROUTES);
        // use the 'where' clause to search through the messages to find where our user ID is one of the recipients
        queryRoute.whereEqualTo(ParseConstants.KEY_ACCEPTED_RECIPIENT_IDS, ParseUser.getCurrentUser().getObjectId());
        // order results so that most recent message are at the top of the inbox
        queryRoute.addDescendingOrder(ParseConstants.KEY_CREATED_AT);
        // query is ready - run it
        queryRoute.findInBackground(new FindCallback<ParseObject>() {
            // When the retrieval is done from the Parse query, the done() callback method is called
            @Override
            public void done(List<ParseObject> routes, ParseException e) {
                // dismiss the progress indicator here
                // getActivity().setProgressBarIndeterminateVisibility(false);

                // End refreshing once routes are retrieved
                // done() is called from onResume() and the OnRefreshListener
                // Need to check that its called from the the OnRefreshListener before ending it
                if (mSwipeRefreshLayout.isRefreshing()) {
                    mSwipeRefreshLayout.setRefreshing(false);
                }

                // the list being returned is a list of routes
                if (e == null) {
                    // successful - routes found.  They are stored as a list in messages
                    mAcceptedRoutes = routes;

                    // adapt this data for the list view, showing the senders name

                    // create an array of strings to store the usernames and set the size equal to that of the list returned
                    String[] usernames = new String[mAcceptedRoutes.size()];
                    // enhanced for loop to go through the list of users and create an array of usernames
                    int i = 0;
                    for (ParseObject message : mAcceptedRoutes) {
                        // get the specific key
                        usernames[i] = message.getString(ParseConstants.KEY_SENDER_NAME);
                        i++;
                    }

                    // Create the adapter once and update its state on each refresh
                    if (getListView().getAdapter() == null) {
                        // the above adapter code is now replaced with the following line
                        RouteMessageAdapter adapter = new RouteMessageAdapter(getListView().getContext(), mAcceptedRoutes);

                        // Force a refresh of the list once data has changed
                        adapter.notifyDataSetChanged();

                        // need to call setListAdapter for this activity.  This method is specifically from the ListActivity class
                        setListAdapter(adapter);
                    } else {
                        // refill the adapter
                        // cast it to RouteMessageAdapter
                        ((RouteMessageAdapter) getListView().getAdapter()).refill(mAcceptedRoutes);
                    }
                }
            }
        });
    }

    protected SwipeRefreshLayout.OnRefreshListener mOnRefreshListener = new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            // When list is swiped down to refresh, retrieve the users runs from the Parse backend
            retrieveAcceptedRoutes();
        }
    };

}

和 fragment_my_runs 布局文件:

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity$PlaceholderFragment">

    <android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/swipeRefreshLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true">

        <ListView
            android:id="@android:id/list"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:clipToPadding="false"
            android:paddingBottom="@dimen/inbox_vertical_margin"/>

    </android.support.v4.widget.SwipeRefreshLayout>

    <TextView
        android:id="@android:id/empty"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/empty_inbox_label"
        android:textSize="@dimen/default_text_size"/>

</RelativeLayout>

TabFragmentContainer

public class TabFragmentContainer extends Fragment {

    // Create the FragmentPagerAdapter that will provide and manage tabs for each section.
    public static MyFragmentPagerAdapter myFragmentPagerAdapter;

    public static TabLayout tabLayout;

    // The ViewPager is a layout widget in which each child view is a separate tab in the layout.
    // It will host the section contents.
    public static ViewPager viewPager;

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

        // Inflate tab_layout_fragment_container view and setup views for the TabLayout and ViewPager items.
        View view = inflater.inflate(R.layout.tab_layout_fragment_container, null);

        tabLayout = (TabLayout) view.findViewById(R.id.tabs);

        // Set up the ViewPager with the sections adapter.
        viewPager = (ViewPager) view.findViewById(R.id.viewpager);

        // Instantiate the adapter that will return a fragment for each of the three sections of the main activity
        myFragmentPagerAdapter = new MyFragmentPagerAdapter(getActivity(), getChildFragmentManager());

        // Set up the adapter for the ViewPager
        viewPager.setAdapter(myFragmentPagerAdapter);

        // Runnable() method required to implement setupWithViewPager() method
        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
                viewPager.setCurrentItem(1, false);
                // tabLayout.getTabAt(1).select();
            }
        });

        // Return the created View
        return view;
    }

}

FragmentPagerAdapter:

public class MyFragmentPagerAdapter extends FragmentPagerAdapter {

    // The context to be passed in when the adapter is created.
    private Context mContext;
    // The number of tabs in the layout.
    public static int numberOfTabs = 3;

    /**
     * Default constructor that accepts a FragmentManager parameter to add or remove fragments.
     *
     * @param context         the context from the activity using the adapter.
     * @param fragmentManager the FragmentManager for managing Fragments inside of the TabFragmentContainer.
     */
    public MyFragmentPagerAdapter(Context context, FragmentManager fragmentManager) {
        super(fragmentManager);
        mContext = context;
    }

    /**
     * Method to return the relevant fragment for the selected tab.
     */
    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new MyRunsFragment();
            case 1:
                return new InboxRouteFragment();
            case 2:
                return new FriendsFragment();
        }
        return null;
    }

    /**
     * Method that gets the number of tabs in the layout.
     *
     * @return the number of tabs in the layout.
     */
    @Override
    public int getCount() {
        return numberOfTabs;
    }

    /**
     * Method that returns the title of each tab in the layout.
     */
    @Override
    public CharSequence getPageTitle(int position) {
        Locale locale = Locale.getDefault();
        switch (position) {
            case 0:
                return mContext.getString(R.string.title_section1).toUpperCase(locale);
            case 1:
                return mContext.getString(R.string.title_section2).toUpperCase(locale);
            case 2:
                return mContext.getString(R.string.title_section3).toUpperCase(locale);
        }
        return null;
    }
}

包含 ViewPager 小部件的 tab_layout_fragment_container 文件:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <android.support.design.widget.TabLayout
        android:id="@+id/tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/ColorPrimaryPurple"
        app:tabGravity="fill"
        app:tabIndicatorColor="@color/ColorPrimaryPurple"
        app:tabMode="fixed"
        app:tabSelectedTextColor="@color/textColorPrimary"
        app:tabTextColor="@color/pressedPurpleButton">
    </android.support.design.widget.TabLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </android.support.v4.view.ViewPager>

</LinearLayout>

我的 MainActivity 中的 onCreate() 方法:

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

    setContentView(R.layout.activity_main);

    // Initialise the DrawerLayout and NavigationView views.
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
    mNavigationView = (NavigationView) findViewById(R.id.navigationDrawerMenu);

    // Inflate the first fragment to be displayed when logged into the app.
    mFragmentManager = getSupportFragmentManager();
    mFragmentTransaction = mFragmentManager.beginTransaction();
    mFragmentTransaction.replace(R.id.containerView, new TabFragmentContainer()).commit();

    // Setup click events on the NavigationView items.
    // When an item is selected, replace the tab fragment container with the requested fragment.
    mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem menuItem) {
            mDrawerLayout.closeDrawers();
            if (menuItem.getItemId() == R.id.navItemHome) {
                FragmentTransaction tabFragmentContainer = mFragmentManager.beginTransaction();
                tabFragmentContainer.replace(R.id.containerView, new TabFragmentContainer()).commit();
            }
            if (menuItem.getItemId() == R.id.navItemRunHistory) {
                FragmentTransaction runHistoryFragment = mFragmentManager.beginTransaction();
                runHistoryFragment.replace(R.id.containerView, new RunHistoryFragment()).commit();
            }
            if (menuItem.getItemId() == R.id.navItemSettings) {
                FragmentTransaction settingsFragment = mFragmentManager.beginTransaction();
                settingsFragment.replace(R.id.containerView, new SettingsFragment()).commit();
            }
            if (menuItem.getItemId() == R.id.navItemHelp) {
                FragmentTransaction instructionsFragment = mFragmentManager.beginTransaction();
                instructionsFragment.replace(R.id.containerView, new InstructionsFragment()).commit();
            }
            if (menuItem.getItemId() == R.id.navItemMyProfile) {
                FragmentTransaction myProfileFragment = mFragmentManager.beginTransaction();
                myProfileFragment.replace(R.id.containerView, new MyProfileFragment()).commit();
            }
            if (menuItem.getItemId() == R.id.navItemLogOut) {
                // User has selected log out option. Log user out and return to login screen.
                ParseUser.logOut();
                navigateToLogin();
            }
            return false;
        }
    });

    // Set up the Toolbar.
    setupToolbar();
}

我在这里遵循了其他答案并将 getListView() 功能添加到 onViewCreated() 方法，但问题仍然存在......任何人都可以指出我在哪里可能出错了？

Answer 1

基于这些事实:

• 当done() 调用getListView() 时，还没有 Root View 而抛出异常。
• done() 在 retrieveAcceptedRoutes() 的查询得到响应时调用。
• retrieveAcceptedRoutes 在多个地方调用，包括 OnRefreshListener mOnRefreshListener，它在 onCreateView() 中注册为刷新监听器 之前有一个 Root View (即，在onCreateView() 返回之前)。

...在有 Root View 之前调用 getListView() 是可能的。

尝试将这 3 个语句从 onCreateView() 移至 onViewCreated()，这样刷新监听器只能在有 Root View 时调用。

    // Set SwipeRefreshLayout component 
    mSwipeRefreshLayout = (SwipeRefreshLayout) rootView.findViewById(R.id.swipeRefreshLayout);
    // Set the onRefreshListener 
    mSwipeRefreshLayout.setOnRefreshListener(mOnRefreshListener);
    mSwipeRefreshLayout.setColorSchemeResources(
            R.color.swipeRefresh1,
            R.color.swipeRefresh2,
            R.color.swipeRefresh3,
            R.color.swipeRefresh4);