导航抽屉头文本视图nullpointerexception [英] Navigation drawer header textview nullpointerexception
本文介绍了导航抽屉头文本视图nullpointerexception的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有2个活动和一个服务，首先我有导航抽屉，标题中有2个文本视图，我必须有时更改文本，在服务中有一些我需要的数据
在第一次运行时，一切都很完美，但是当我从第二个进行第一个活动时，我在textviews中有nullpointerexception。是什么导致它，以及如何解决？
I have an 2 activity and a service, in first I have navigation drawer, and 2 textviews in its header, and I must change their text sometimes, in service there is some data that i need
On first run everything is perfect, but when I go to the first activity from second, I have nullpointerexception in textviews. What causes it, and how to fix?
//First
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Navigation drawer init
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbarMain);
setSupportActionBar(toolbar);
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.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view_main);
navigationView.setNavigationItemSelectedListener(this);
intent = new Intent("playbackservice");
sConn = new ServiceConnection() {
public void onServiceConnected(ComponentName name, IBinder binder) {
Log.d(LOG_TAG, "MainActivity onServiceConnected");
service = ((PlaybackService.PlaybackServiceBinder) binder).getService();
bound = true;
prepareLayout();
}
public void onServiceDisconnected(ComponentName name) {
Log.d(LOG_TAG, "MainActivity onServiceDisconnected");
bound = false;
}
};
}
private void prepareLayout() {
Log.d(LOG_TAG, "prepareLayout: Running");
((TextView) findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
((TextView) findViewById(R.id.artistNavhead)).setText(currentSong.getArtist());
}
和
//Layout nav_header_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="@dimen/nav_header_height"
android:gravity="bottom"
android:orientation="vertical"
android:background="@color/colorPrimaryDark"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:theme="@style/ThemeOverlay.AppCompat.Dark">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="@string/default_song_name"
android:id="@+id/songNameNavhead"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/default_artist"
android:id="@+id/artistNavhead"/>
</LinearLayout>
和
//activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
android:id="@+id/drawer_layout"
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: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_main"
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"/>
</android.support.v4.widget.DrawerLayout>
错误
05-12 19:34:05.001 11086-11086/iskandarovlev.myitschool.ru.lyricplayer E/AndroidRuntime: FATAL EXCEPTION: main
Process: iskandarovlev.myitschool.ru.lyricplayer, PID: 11086
java.lang.NullPointerException
//MainActivity.java:302 is
//((TextView) header.findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
//this line
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity.prepareLayout(MainActivity.java:302)
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity.access$700(MainActivity.java:48)
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity$3.onServiceConnected(MainActivity.java:355)
at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1140)
at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1157)
at android.os.Handler.handleCallback(Handler.java:808)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5542)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:657)
at dalvik.system.NativeStart.main(Native Method)
推荐答案
要在Navigation Drawer的标题中成功查找小部件，你需要首先获得它的标题视图，这可以通过使用 getHeaderView（）方法：
To successfuly look for widget in Navigation Drawer's header, you need to obtain its header view first, which can be achieved with use of getHeaderView() method:
View header = ((NavigationView)findViewById(R.id.navigation_view)).getHeaderView(0);
然后，指向右边的标题 ViewGroup ，您可以像往常一样使用常规 findViewById（）：
Then, having header pointing to the right ViewGroup, you can use regular findViewById() on it as usual:
TextView tv = header.findViewById(R.id.songNameNavhead);
tv.setText(currentSong.getName());
或者更紧凑：
((TextView)header.findViewById(R.id.songNameNavhead))
.setText(currentSong.getName());
这篇关于导航抽屉头文本视图nullpointerexception的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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