在导航抽屉标题中添加TextView项目的代码

Question

我目前在我的应用程序中使用NavigationView实施了导航抽屉。抽屉的布局分为标题drawer_header.xml和菜单drawer_menu.xml。它看起来是这样的：

我试图使用setText代替xml但是我收到以下错误，在Java代码中头设置用户名DrawerNameTv：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

这里的Main_Activity.java

TextView DrawerName; 

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

    CustomToolbar = (Toolbar) findViewById(R.id.toolbar); 
    DrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout); 
    NavigationView = (NavigationView) findViewById(R.id.navigation_view); 
    DrawerName = (TextView) findViewById(R.id.DrawerNameTv); 

    DrawerName.setText("Test"); 

    ... 

而drawer_header.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <ImageView 
     android:layout_width="100dp" 
     android:layout_height="100dp" 
     android:src="@drawable/user_pic" /> 

    <TextView 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent" 
     android:textSize="20dp" 
     android:layout_marginTop="120dp" 
     android:id="@+id/DrawerNameTv" /> 

</RelativeLayout> 

对不起，因为我是Android开发新手。

Answer 1

视图DrawerNameTv没有在你指的布局中，这就是为什么它给你一个NullPointerException。您需要像这样在NavigationView内找到DrawerNameTv。

里面你onCreate功能

// lets change the variable names first. 
private NavigationView mNavigationView; 

mNavigationView = (NavigationView) findViewById(R.id.navigation_view); 
DrawerName = (TextView) mNavigationView.getHeaderView(0).findViewById(R.id.DrawerNameTv); 

// Now set the text here 
DrawerName.setText("Test"); 

Answer 2

在你的课堂上添加以下功能。

public boolean onNavigationItemSelected(MenuItem item) { 
    // Handle navigation view item clicks here. 
    int id = item.getItemId(); 

    switch(id){ 
     case R.id.nav_home: 
      // call your page from here 
      break; 
     case R.id.nav_message: 
      // call your page from here 
      break; 
     case R.id.nav_setting: 
      // call your page from here 
      break; 
    } 

DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
       drawer.closeDrawer(GravityCompat.START); 
       return true; 
      }