尝试在抽屉菜单中设置项目的标题时出现NullPointerException

-1

在包含min SDK v。16和目标SDK v。23的Android应用程序中，我想以编程方式更改属于抽屉菜单的菜单项的标题。我认为这将是做一个简单的问题：尝试在抽屉菜单中设置项目的标题时出现NullPointerException

MenuItem myMenuItem = (MenuItem) findViewById(R.id.nav_gallery); 
myMenuItem.setTitle("New title"); // <---------- NullPointerException

，但我显然不正确地访问对象：

logcat的：

02-22 19:10:16.707 5798-5798/? E/AndroidRuntime: FATAL EXCEPTION: main 
java.lang.NullPointerException 
at com.example.myapp.MainActivity.onCreateOptionsMenu(MainActivity.java:86) 
at android.app.Activity.onCreatePanelMenu(Activity.java:2476) 
at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:298) 
at android.support.v7.view.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:85) 
at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.onCreatePanelMenu(AppCompatDelegateImplBase.java:241) 
at android.support.v7.view.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:85) 
at android.support.v7.app.ToolbarActionBar.populateOptionsMenu(ToolbarActionBar.java:443) 
at android.support.v7.app.ToolbarActionBar$1.run(ToolbarActionBar.java:60) 
at android.os.Handler.handleCallback(Handler.java:615) 
at android.os.Handler.dispatchMessage(Handler.java:92) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4745) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
at dalvik.system.NativeStart.main(Native Method)

任何想法？下面是相关代码：

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?> 
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:id="@+id/drawer_layout" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:fitsSystemWindows="true" 
tools:openDrawer="start"> 

<include 
    layout="@layout/app_bar_main" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" /> 

<android.support.design.widget.NavigationView 
    android:id="@+id/nav_view" 
    android:layout_width="wrap_content" 
    android:layout_height="match_parent" 
    android:layout_gravity="start" 
    android:fitsSystemWindows="true" 
    app:headerLayout="@layout/nav_header_main" 
    app:menu="@menu/activity_main_drawer" />

activity_main_drawer.xml

<?xml version="1.0" encoding="utf-8"?> 
<menu xmlns:android="http://schemas.android.com/apk/res/android"> 

<group android:checkableBehavior="single"> 
    <item 
     android:id="@+id/nav_camera" 
     android:icon="@drawable/ic_menu_camera" 
     android:title="Import" /> 
    <item 
     android:id="@+id/nav_gallery" 
     android:icon="@drawable/ic_menu_gallery" 
     android:title="Gallery" />  <!-- I want to change the title of this item --> 
    <item 
     android:id="@+id/nav_slideshow" 
     android:icon="@drawable/ic_menu_slideshow" 
     android:title="Slideshow" /> 
    <item 
     android:id="@+id/nav_manage" 
     android:icon="@drawable/ic_menu_manage" 
     android:title="Tools" /> 
</group> 

<item android:title="Communicate"> 
    <menu> 
     <item 
      android:id="@+id/nav_share" 
      android:icon="@drawable/ic_menu_share" 
      android:title="Share" /> 
     <item 
      android:id="@+id/nav_send" 
      android:icon="@drawable/ic_menu_send" 
      android:title="Send" /> 
    </menu> 
</item>

MainActivity.java：

public class MainActivity extends AppCompatActivity 
    implements NavigationView.OnNavigationItemSelectedListener { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
        .setAction("Action", null).show(); 
     } 
    }); 

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
      this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
    drawer.setDrawerListener(toggle); 
    toggle.syncState(); 

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view); 
    navigationView.setNavigationItemSelectedListener(this); 
} 


@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); 

    MenuItem myMenuItem = (MenuItem) findViewById(R.id.nav_gallery); 
    myMenuItem.setTitle("New title"); // <---------- NullPointerException 

    return true; 
} 
...

来源

2016-02-22 Javide

你在哪里添加你的'activity_main_drawer.xml'到菜单？ –

可能重复http://stackoverflow.com/questions/31265530/how-can-i-get-menu-item-in-navigationview?answertab=oldest#tab-top –

您应该使用navigationView.getMenu().findItem(R.id.nav_gallery)代替。

来源

2016-02-22 08:33:15 Artem

NavigationView nav_draw =（NavigationView）findViewById（R.id .nav_view）; nav_draw.getMenu（）。findItem（R.id.nav_gallery）.setTitle（“New title”）; – Javide

使用下面的代码来获得菜单项：

@Override 
    public void onPrepareOptionsMenu(Menu menu) { 
     MenuItem gallery = menu.findItem(R.id.nav_gallery); 
     gallery.setTitle("New title"); 
    }

来源

2016-02-22 08:37:35

这引发相同的NullPointerException。 – Javide

使用此代码在 public void onPrepareOptionsMenu（Menu menu）{}方法 –

同样的问题。请注意，它应该是“公共布尔”。 – Javide

尝试在抽屉菜单中设置项目的标题时出现NullPointerException

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