抽屉关闭时的Android Navigation-Drawer NullPointerException答案

【问题标题】：Android Navigation-Drawer NullPointerException when drawer close抽屉关闭时的Android Navigation-Drawer NullPointerException
【发布时间】：2014-03-03 15:30:52
【问题描述】：

我正在通过修改http://developer.android.com/training/implementing-navigation/nav-drawer.html 处的“示例应用”代码来制作自己的导航抽屉

我不想使用片段。每当我在抽屉中选择一个选项时，我只想去参加一项新活动。问题是，当我从我的 activity_main.xml 中删除 FrameLayout 时，我得到一个 NullPointerException 但如果我不删除它，我不会得到异常......我不明白为什么会发生这种情况，因为我不是在任何地方使用该 FrameLayout。

这是我的 MainActivity。

    public class MainActivity extends Activity {
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

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

    // load slide menu items
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();

    // adding nav drawer items to array
    // History
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
    // Contacts
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
    // Information
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
    // Check out
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button
    getActionBar().setDisplayShowHomeEnabled(true);
    getActionBar().setDisplayHomeAsUpEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            R.drawable.ic_drawer, //nav menu toggle icon
            R.string.app_name, // nav drawer open - description for accessibility
            R.string.app_name // nav drawer close - description for accessibility
            ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(R.string.empty);
            // calling onPrepareOptionsMenu() to show action bar icons
            //              invalidateOptionsMenu();
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(R.string.back_to_JobList);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);
}

/**
 * Slide menu item click listener
 * */
private class SlideMenuClickListener implements
ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {
        // display view for selected nav drawer item
        displayView(position);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

public boolean onOptionsItemSelected(MenuItem item) {


    // toggle nav drawer on selecting action bar app icon/title
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action bar actions click
    // Handle presses on the action bar items
    switch (item.getItemId()) {
    case R.id.map_view:
        Toast.makeText(getApplicationContext(), "Map view pressed",
                Toast.LENGTH_LONG).show();
        //startActivity(GoogleMapsActivity.class);
        return true;


    case R.id.infrastucture_only:
        Toast.makeText(getApplicationContext(),
                "Infrastucture only pressed", Toast.LENGTH_LONG).show();
        return true;
    case R.id.infrastucture_map:
        Toast.makeText(getApplicationContext(),
                "Infrastucture + map pressed", Toast.LENGTH_LONG).show();
        return true;
    case R.id.camera_only:
        Toast.makeText(getApplicationContext(), "Camera only pressed",
                Toast.LENGTH_LONG).show();
        return true;
    case R.id.camera_infrastucture:

        Toast.makeText(getApplicationContext(),
                "Infrastucture + Camera pressed", Toast.LENGTH_LONG).show();
        //startActivity(MetaioActivity.class);
        return true;
    default:
        return super.onOptionsItemSelected(item);
    }
}

/* *
 * Called when invalidateOptionsMenu() is triggered
 */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // if nav drawer is opened, hide the action items
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.dots_menu).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

/**
 * Diplaying fragment view for selected nav drawer list item
 * */
private void displayView(int position) {

    switch (position) {
    case 0:
        Toast.makeText(getApplicationContext(),
                "History pressed", Toast.LENGTH_LONG).show();
        Intent intent = new Intent(this, Teste.class);
        startActivity(intent);
        break;

    case 1:
        Toast.makeText(getApplicationContext(),
                "Contacts pressed", Toast.LENGTH_LONG).show();
        break;

    case 2:
        Toast.makeText(getApplicationContext(),
                "Information pressed", Toast.LENGTH_LONG).show();
        break;

    case 3:
        Toast.makeText(getApplicationContext(),
                "Check out pressed", Toast.LENGTH_LONG).show();
        break;


    default:
        break;
    }       
}


/**
 * When using the ActionBarDrawerToggle, you must call it during
 * onPostCreate() and onConfigurationChanged()...
 */

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggls
    mDrawerToggle.onConfigurationChanged(newConfig);
}

    }

这是我的 activity_main.xml

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

  <!-- Framelayout to display Fragments -->
<FrameLayout
    android:id="@+id/frame_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<!-- Listview to display slider menu -->
<ListView
    android:id="@+id/list_slidermenu"
    android:layout_width="240dp"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:choiceMode="singleChoice"
    android:divider="@color/list_divider"
    android:dividerHeight="1dp"        
    android:listSelector="@drawable/list_selector"
    android:background="@color/list_background"/>
 </android.support.v4.widget.DrawerLayout>

很好，这是 log-cat 的输出

03-03 15:00:07.317: E/Trace(810): error opening trace file: No such file or directory    (2)
03-03 15:00:08.058: I/Choreographer(810): Skipped 41 frames!  The application may be doing too much work on its main thread.
03-03 15:00:08.087: D/gralloc_goldfish(810): Emulator without GPU emulation detected.
03-03 15:00:10.867: E/InputEventReceiver(810): Exception dispatching input event.
03-03 15:00:10.867: E/MessageQueue-JNI(810): Exception in MessageQueue callback: handleReceiveCallback
03-03 15:00:10.938: E/MessageQueue-JNI(810): java.lang.NullPointerException
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at   android.support.v4.widget.DrawerLayout.isContentView(DrawerLayout.java:853)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.support.v4.widget.DrawerLayout.onInterceptTouchEvent(DrawerLayout.java:879)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1822)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1925)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1379)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.app.Activity.dispatchTouchEvent(Activity.java:2396)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1873)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.View.dispatchPointerEvent(View.java:7307)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3174)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3119)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4155)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4134)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4226)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.os.MessageQueue.nativePollOnce(Native Method)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.os.MessageQueue.next(MessageQueue.java:125)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.os.Looper.loop(Looper.java:124)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at android.app.ActivityThread.main(ActivityThread.java:4745)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at java.lang.reflect.Method.invokeNative(Native Method)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at java.lang.reflect.Method.invoke(Method.java:511)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-03 15:00:10.938: E/MessageQueue-JNI(810):    at dalvik.system.NativeStart.main(Native Method)
03-03 15:00:10.938: D/AndroidRuntime(810): Shutting down VM
03-03 15:00:10.938: W/dalvikvm(810): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
03-03 15:00:11.058: E/AndroidRuntime(810): FATAL EXCEPTION: main
03-03 15:00:11.058: E/AndroidRuntime(810): java.lang.NullPointerException
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.support.v4.widget.DrawerLayout.isContentView(DrawerLayout.java:853)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.support.v4.widget.DrawerLayout.onInterceptTouchEvent(DrawerLayout.java:879)
03-03 15:00:11.058: E/AndroidRuntime(810):  at    android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1822)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2176)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1877)
03-03 15:00:11.058: E/AndroidRuntime(810):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.j ava:1925)
03-03 15:00:11.058: E/AndroidRuntime(810):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1379)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.app.Activity.dispatchTouchEvent(Activity.java:2396)
03-03 15:00:11.058: E/AndroidRuntime(810):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1873)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.View.dispatchPointerEvent(View.java:7307)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3174)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3119)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4155)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4134)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4226) 
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.os.MessageQueue.nativePollOnce(Native Method)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.os.MessageQueue.next(MessageQueue.java:125)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.os.Looper.loop(Looper.java:124)
03-03 15:00:11.058: E/AndroidRuntime(810):  at android.app.ActivityThread.main(ActivityThread.java:4745)
03-03 15:00:11.058: E/AndroidRuntime(810):  at java.lang.reflect.Method.invokeNative(Native Method)
03-03 15:00:11.058: E/AndroidRuntime(810):  at java.lang.reflect.Method.invoke(Method.java:511)
03-03 15:00:11.058: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-03 15:00:11.058: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-03 15:00:11.058: E/AndroidRuntime(810):  at dalvik.system.NativeStart.main(Native Method)
03-03 15:00:11.168: D/dalvikvm(810): GC_CONCURRENT freed 257K, 10% free 7438K/8199K, paused 74ms+16ms, total 207ms
03-03 15:05:11.188: I/Process(810): Sending signal. PID: 810 SIG: 9

【问题讨论】：

标签： android nullpointerexception navigation-drawer android-framelayout

【解决方案1】：

如您附加的链接中所述：

要添加导航抽屉，请使用 DrawerLayout 对象声明您的用户界面作为布局的根视图。在 DrawerLayout 中，添加一个包含屏幕主要内容的视图（隐藏抽屉时的主要布局）和另一个包含导航抽屉内容的视图。

这意味着 DrawerLayout 期望获得 2 个视图 - 一个是主视图，另一个是抽屉。如果您删除 FrameLayout，则需要添加一个虚拟视图。

【讨论】：

【解决方案2】：

根据Android Doc about create an Navigation Drawer，您需要为具有两个子视图的布局创建android.support.v4.widget.DrawerLayout 作为根：FragmentLayout 和ListView

因为the XML order implies z-ordering and the drawer must be on top of the content.

如果你不需要使用FragmentLayout视图，你可以让它的visibility是gone

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

      <!-- Framelayout to display Fragments -->
    <FrameLayout
        android:id="@+id/frame_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone" />

    <!-- Listview to display slider menu -->
    <ListView
        android:id="@+id/list_slidermenu"
        android:layout_width="240dp"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:choiceMode="singleChoice"
        android:divider="@color/list_divider"
        android:dividerHeight="1dp"        
        android:listSelector="@drawable/list_selector"
        android:background="@color/list_background"/>
</android.support.v4.widget.DrawerLayout>

【讨论】：