我的Android应用程序中有一个DrawerLayout，它有一个使用nav_header_main2布局的NavigationView。在nav_header_main2布局文件中有一个ImageView和2个TextViews，在我的MainActivity中我试图抓取那些TextView项目，这样我就可以使用用户名和电子邮件地址动态填写内容，但每当我尝试时，我总是得到一个空引用访问它们。 这是主要的布局文件......
<?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_main2"
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_main2"
app:menu="@menu/activity_main2_drawer"/>
</android.support.v4.widget.DrawerLayout>
如您所见，NavigationView正在使用“nav_header_main2”，这是该文件......
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="@dimen/nav_header_height"
android:background="@drawable/side_nav_bar"
android:gravity="bottom"
android:orientation="vertical"
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">
<de.hdodenhof.circleimageview.CircleImageView
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/menu_user_photo"
android:layout_width="64dp"
android:layout_height="64dp"
android:layout_gravity="center_horizontal"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:src="@drawable/ic_person_white"
app:border_color="@color/colorTransparent"
android:layout_marginStart="10dp"
android:layout_marginLeft="10dp"
android:layout_marginTop="3dp"
android:layout_marginBottom="0dp"
app:border_width="1dp"/>
<!--<ImageView-->
<!--android:id="@+id/imageView"-->
<!--android:layout_width="wrap_content"-->
<!--android:layout_height="wrap_content"-->
<!--android:paddingTop="@dimen/nav_header_vertical_spacing"-->
<!--app:srcCompat="@android:drawable/sym_def_app_icon"/>-->
<TextView
android:id="@+id/menu_username"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="@dimen/nav_header_vertical_spacing"
android:layout_gravity="center_horizontal"
android:gravity="center_horizontal"
android:text="Android Studio"
android:textAppearance="@style/TextAppearance.AppCompat.Body1"/>
<TextView
android:id="@+id/textView"
android:gravity="center_horizontal"
android:layout_gravity="center_horizontal"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="android.studio@android.com"/>
</LinearLayout>
然后在我的MainActivity中，我尝试了多种方法来访问“menu_username”项，但所有这些方法都返回一个空引用。这是我现在的主要课程......
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
public static final String EXTRA_MESSAGE = "text.notreal.justatest.MESSAGE";
public static final int TAG_KEY = 0;
public static final int TAG_VALUE = 0;
public List<Post> posts = new ArrayList<>();
public FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
@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);
//THIS IS WHAT IS FAILING
//I HAVE ALSO TRIED JUST USING findViewById(R.id.menu_username); NULL STILL
TextView menuUserName = (TextView) navigationView.findViewById(R.id.menu_username);
if(menuUserName == null) {
Log.d("MAIN ACTIVITY", "Somehow the menu_username doesn't exist");
}
if(findViewById(R.id.frameLayout) != null) {
if(savedInstanceState != null) {
return;
}
AllPostsFragment fragment = new AllPostsFragment();
fragment.setArguments(getIntent().getExtras());
getSupportFragmentManager().beginTransaction().add(R.id.frameLayout, fragment).commit();
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()) {
case android.R.id.home:
this.finish();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_camera) {
// Handle the camera action
} else if (id == R.id.nav_gallery) {
} else if (id == R.id.nav_slideshow) {
} else if (id == R.id.nav_manage) {
} else if (id == R.id.nav_share) {
} else if (id == R.id.nav_send) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
正如您所看到的，我正在尝试使用NavigationView对象来抓取它，但是我也尝试使用
TextView menuUsername = (TextView) findViewById(R.id.menu_username);
也返回空引用。如何在主活动中获取用户名和电子邮件字段，以便我可以动态填写内容？谢谢
答案 0 :(得分：4)
你不会那样找到它。正确的方法是首先找到您的NavigationView，然后使用getHeaderView()获取HeaderView，然后在HeaverView中搜索您的小部件：
NavigationView nv = findViewById(R.id.nav_view);
TextView menuUsername = nv.getHeaderView(0).findViewById(R.id.menu_username);
或更紧凑的方式
TextView menuUsername = findViewById(R.id.nav_view)
.getHeaderView(0).findViewById(R.id.menu_username);