Java 尝试在抽屉菜单中设置项目标题时出现NullPointerException
在一个带有min SDK v的Android应用程序上。16和目标SDK v。23我想以编程方式更改属于抽屉菜单的菜单项的标题。我认为这将是一个简单的事情：Java 尝试在抽屉菜单中设置项目标题时出现NullPointerException,java,android,nullpointerexception,menuitem,navigation-drawer,Java,Android,Nullpointerexception,Menuitem,Navigation Drawer,在一个带有min SDK v的Android应用程序上。16和目标SDK v。23我想以编程方式更改属于抽屉菜单的菜单项的标题。我认为这将是一个简单的事情： MenuItem myMenuItem = (MenuItem) findViewById(R.id.nav_gallery); myMenuItem.setTitle("New title"); // <---------- NullPointerException 有什么想法吗？以下是相关代码： 活动\u main.xml &l
MenuItem myMenuItem = (MenuItem) findViewById(R.id.nav_gallery);
myMenuItem.setTitle("New title"); // <---------- NullPointerException
<?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" />
<?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>
<?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" />
<?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>
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)
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;
}
...
public类MainActivity扩展了AppCompatActivity
实现NavigationView.OnNavigationItemSelectedListener{
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
Toolbar Toolbar=（Toolbar）findViewById（R.id.Toolbar）；
设置支持操作栏（工具栏）；
FloatingActionButton fab=（FloatingActionButton）findViewById（R.id.fab）；
fab.setOnClickListener（新视图.OnClickListener（）{
@凌驾
公共void onClick（视图）{
Snackbar.make（查看“替换为您自己的操作”，Snackbar.LENGTH\u LONG）
.setAction（“Action”，null）.show（）；
}
});
抽屉布局抽屉=（抽屉布局）findViewById（R.id.抽屉布局）；
ActionBarDrawerToggle切换=新建ActionBarDrawerToggle(
这，抽屉，工具栏，R.string.navigation\u drawer\u open，R.string.navigation\u drawer\u close）；
抽屉。设置抽屉定位器（开关）；
toggle.syncState（）；
NavigationView NavigationView=（NavigationView）findViewById（R.id.nav_视图）；
navigationView.setNavigationItemSelectedListener（此）；
}
@凌驾
公共布尔onCreateOptions菜单（菜单）{
//为菜单充气；这会将项目添加到操作栏（如果存在）。
getMenuInflater（）.充气（R.menu.main，menu）；
MenuItem myMenuItem=（MenuItem）findViewById（R.id.nav_画廊）；
myMenuItem.setTitle（“新标题”）；//您应该改用navigationView.getMenu（）.findItem（R.id.nav_gallery）
。您应该改用navigationView.getMenu（）.findItem（R.id.nav_gallery）
。使用以下代码获取菜单项：
@Override
public void onPrepareOptionsMenu(Menu menu) {
MenuItem gallery = menu.findItem(R.id.nav_gallery);
gallery.setTitle("New title");
}
使用以下代码获取菜单项：
@Override
public void onPrepareOptionsMenu(Menu menu) {
MenuItem gallery = menu.findItem(R.id.nav_gallery);
gallery.setTitle("New title");
}
将activity\u main\u drawer.xml
添加到菜单的位置？可能重复将activity\u main\u drawer.xml
添加到菜单的位置？可能重复此操作会引发相同的NullPointerException。在public void onPrepareOptions菜单（菜单菜单菜单）中使用此代码{}方法相同问题。请注意，它应该是“public boolean”.NavigationView nav_draw=（NavigationView）FindView nav_draw=（R.id.nav_视图）；nav_draw.getMenu（）.findItem（R.id.nav_gallery）.设置标题（“新标题”）；NavigationView nav_draw=（NavigationView）findViewById（R.id.nav_视图）；nav_draw.getMenu（）.findItem（R.id.nav_gallery）.setTitle（“新标题”）；