导航抽屉中的片段未加载并导致应用程序崩溃。我能做些什么？

Question

因此，我使用以下代码为我的程序构建了一个导航抽屉：

这是主要的xml:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".HomeScreen">

        <include
            android:id="@+id/eb_bar"
            layout="@layout/eb_bar" />

        <FrameLayout
            android:id="@+id/main_screen"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_below="@+id/eb_bar"
            android:background="@color/frame_layout_bg"/>

    </RelativeLayout>

    <fragment
        android:id="@+id/frag_navigation_drawer"
        android:layout_width="@dimen/navigation_drawer_width"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:layout="@layout/fragment_navigation_drawer"
        android:name="com.myapps.project.NavigationDrawerFragment"
        tools:layout="@layout/fragment_navigation_drawer"
        />

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

这是导航抽屉的 xml：

<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"
    android:background="@color/navigation_drawer_background"
    tools:context="com.myapps.project.NavigationDrawerFragment">

    <FrameLayout
        android:id="@+id/nav_drawer_frame_logo"
        android:layout_width="match_parent"
        android:layout_height="160dp"
        android:background="@color/splash_screen_bg"
        android:elevation="3dp">

        <ImageView
            android:id="@+id/nav_drawer_logo"
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_marginLeft="@dimen/navigation_drawer_center_logo"
            android:layout_marginStart="@dimen/navigation_drawer_center_logo"
            android:src="@drawable/logo"
            tools:ignore="ContentDescription" />
    </FrameLayout>

    <ListView
        android:id="@+id/nav_drawer_menu_ListView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/nav_drawer_frame_logo"
        android:choiceMode="singleChoice"
        android:divider="@color/divider_color"
        android:dividerHeight="1dp"
        />

</RelativeLayout>

这是我要加载的片段的 xml：

<FrameLayout
 xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/Second_screen"
    android:tag="Second"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#00F"
    tools:context="com.myapps.project.Second_Screen"
    android:name="com.myapps.project.Second_Screen"
    tools:layout="@layout/fragment_second_screen">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_second_screen" />

</FrameLayout>

我也有两个.java。一个用于主屏幕，一个用于导航抽屉。在主屏幕上我有这个代码：

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home_screen);


        toolBar = (Toolbar) findViewById(R.id.eb_bar);
        setSupportActionBar(toolBar);

        getSupportActionBar().setTitle(null);

        TextView toolbar_home_title = (TextView) findViewById(R.id.home_toolbar_textview);
        toolbar_home_title.setText(R.string.home_screen_title);
        toolbar_home_title.setTextColor(getResources().getColor(R.color.toolbar_txt_color));

        toolBar.setBackgroundColor(getResources().getColor(R.color.toolbar_bg));

        NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.frag_navigation_drawer);

        navDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawerFragment.setUp(R.id.frag_navigation_drawer,
                navDrawerLayout, toolBar);

        navDrawerMenuItems = getResources().getStringArray(R.array.navigation_drawer_items);

        navDrawerListView = (ListView) findViewById(R.id.nav_drawer_menu_ListView);

        FragNavigationDrawer = (FrameLayout) findViewById(R.id.frag_navigation_drawer);

        navDrawerListView.setAdapter(new ArrayAdapter<String>(
                this,
                R.layout.navigation_drawer_list_item,
                navDrawerMenuItems));

        navDrawerListView.setOnItemClickListener(new DrawerItemClickListener());
    }

    public class DrawerItemClickListener implements ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView parent, View view, int position, long id) {
            selectItem(position);
        }
    }

    public void selectItem(int position) {

        String a = navDrawerMenuItems[position];

        Fragment navFragment = getSupportFragmentManager().findFragmentByTag(a);

        android.support.v4.app.FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.main_screen, navFragment)
                .commit();

        navDrawerListView.setItemChecked(position,true);
        navDrawerLayout.closeDrawer(FragNavigationDrawer);
    }

navDrawerMenuItems 数组具有加载到抽屉中作为可点击项目的名称。它们也是我要在屏幕上加载的每个片段的标签。因此，我在 selectItem 中尝试做的是通过其标签加载片段，将其替换到主屏幕上并在最后关闭抽屉。但是这段代码显示错误：

2449-2449/com.myapps.project E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.myapps.project, PID: 2449
java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference
        at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:416)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:451)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:443)
        at com.myapps.project.MainScreen.selectItem(MainScreen.java:106)
        at com.myapps.project.MainScreen$DrawerItemClickListener.onItemClick(MainScreen.java:88)
        at android.widget.AdapterView.performItemClick(AdapterView.java:300)
        at android.widget.AbsListView.performItemClick(AbsListView.java:1143)
        at android.widget.AbsListView$PerformClick.run(AbsListView.java:3044)
        at android.widget.AbsListView.run(AbsListView.java:3833)
        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:5221)
        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:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

我做错了什么？

Answer 1

您应该导入 android.support。v4.app.FragmentManager 而不是 android.app.FragmentManager。然后试试这个

FragmentManager fragmentManager = getSupportFragmentManager();

更新

你能检查一下吗？

<fragment
    android:id="@+id/frag_navigation_drawer">

xml 中的上一行是片段的 id。您将其作为框架布局投射到 java 文件中。

FragNavigationDrawer = (FrameLayout) findViewById(R.id.frag_navigation_drawer);

导航抽屉中的片段未加载并导致应用程序崩溃。我能做些什么？

Fragment in Navigation Drawer not loading and makes the app crash. What can I do?

navigation

android

drawer

android-fragments