NavigationView header中的TextView返回null

Question

我正在使用NavigationView，它有一個標題佈局，該標題佈局包含一個textview，我試圖在我的Activity中訪問它並返回null。

試過花很多時間在上面，沒有希望。

我的動態

public class MainActivity extends AppCompatActivity { 

    private DrawerLayout mDrawerLayout; 
    RelativeLayout headerLL; 
    ImageView userIV; 
    TextView usernameTV; 

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

     headerLL = (RelativeLayout) findViewById(R.id.navHeaderLL); 
     userIV = (ImageView) findViewById(R.id.userDPIV); 
     usernameTV = (TextView) findViewById(R.id.usernameTV); 
     //getting error here 
     usernameTV.setText("Ashiq"); 



     initializeDrawer(); 

    } 
} 

activity_mail.xml

<?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_height="match_parent" 
     android:layout_width="match_parent" 
     android:fitsSystemWindows="true" 
     tools:context=".MainActivity"> 

     <include layout="@layout/include_list_viewpager"/> 

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

    </android.support.v4.widget.DrawerLayout> 

nav_header.xml

<?xml version="1.0" encoding="utf-8"?> 
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
     android:layout_width="match_parent" 
     android:layout_height="192dp" 
     xmlns:tools="http://schemas.android.com/tools" 
     android:background="?attr/colorPrimaryDark" 
     android:padding="16dp" 
     android:id="@+id/navHeaderLL" 
     android:theme="@style/ThemeOverlay.AppCompat.Dark"> 

     <ImageView 
      android:layout_width="100dp" 
      android:layout_height="100dp" 
      android:id="@+id/userDPIV" 
      android:elevation="4dp" 
      android:layout_above="@+id/usernameTV" 
      android:layout_marginBottom="10dp" 
      tools:src="@drawable/ic_menu" 
      /> 

     <TextView 
      android:id="@+id/usernameTV" 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      style="@style/TextViewAppearance.UserName" 
      tools:text="Username" 
     android:layout_alignParentBottom="true" 
     android:textAppearance="@style/TextAppearance.AppCompat.Body1"/> 

</RelativeLayout> 

Answer 1

做次是。

1. 你應該初始化NavigationView

2.After（的未來的setContentView），初始化導航視圖元素

更改代碼如下

public class MainActivity extends AppCompatActivity { 
    private DrawerLayout mDrawerLayout; 
    RelativeLayout headerLL; 
    ImageView userIV; 
    TextView usernameTV; 

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

     // 1 
     initializeDrawer(); 

     //2 

     headerLL = (RelativeLayout) findViewById(R.id.navHeaderLL); 
     userIV = (ImageView) findViewById(R.id.userDPIV); 
     usernameTV = (TextView) findViewById(R.id.usernameTV); 
     //getting error here 
     usernameTV.setText("Ashiq"); 


    } 
} 

希望這有助於。

編碼快樂:)

Answer 2

後初始化NavigationView你趕上與navigationView.getHeaderView充氣頭（0），並使用findViewById獲得查看

navigationView = (NavigationView) findViewById(R.id.nav_view); 
(TextView) navigationView.getHeaderView(0).findViewById(R.id.viewName);