不同布局中的 findViewById（找不到 BottomNavigationView）

Question

我正在开发一个应用程序，因此当您单击登录按钮时，它会显示一个带有底部菜单的屏幕。但是我在将侦听器设置为菜单中的项目时遇到了问题。问题是当我尝试使用 findViewById 查找我的 BottomNavigationView 时，它会在我的 activity_main 而不是我放置它的片段 (welcome_fragment) 中寻找它，因为我只希望它在什么时候显示有人已登录。因此我将获得 null 作为 BottomNavigationView。

我已经尝试在我的方法 "welcomePage" 中设置 setContentView(R.layout.welcome_fragment) ，它确实做到了，这样它就会找到它并且它不会为空。但是，这会导致许多其他错误，例如 “没有找到 id 0x7f080032 (com.example.MyAPP:id/container) 片段 WelcomePage{9547e9f #1 id=0x7f080032} 的视图”，所以我认为这不是正确的处理方式。

这是我的 MainActivity：

    public class MainActivity extends AppCompatActivity {

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


        FragmentManager fm = getFragmentManager();
        Login loggingIn= new Login();
        fm.beginTransaction().replace(R.id.container, loggingIn).commit();
    }

     //When button is pressed we get into this function
     public void finishProcess(){

        WelcomePage wp = new WelcomePage();
        FragmentManager fm = getFragmentManager();
        fm.beginTransaction().addToBackStack(null);
        fm.beginTransaction().replace(R.id.container, wp).commit();


        try {
         //Here is where I get null, because we are looking in activity_main
         BottomNavigationView bottomNav=findViewById(R.id.bottomnavigate);
         bottomNavigation.setOnNavigationItemSelectedListener(menuListener);}
            catch (Exception e) {
                System.out.println(e);
            }
        }}

    //Have tried this one and it works fine
    private BottomNavigationView.OnNavigationItemSelectedListener menuListener 
     = new BottomNavigationView.OnNavigationItemSelectedListener() {...}
}

这是我的 WelcomeFragment：

    public class WelcomePage extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
        return inflater.inflate(R.layout.welcome_fragment, container, false)}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}

这是我对 welcome_fragment 的布局：


<RelativeLayout 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"
    tools:context=".WelcomePage"
    android:background="@drawable/welcomegradient">

    <FrameLayout
        android:id="@+id/showing_page"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/bottomnavigate">
    </FrameLayout>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/bottomnavigate"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        app:menu="@menu/mymenu"
        android:background="?android:attr/windowBackground" />


</RelativeLayout>

正如我之前提到的，问题是 findViewById 找不到 BottomNavigationView，因为它在 activity_main 而不是 welcome_fragment 中查找，我不想将我的菜单放在 activity_main 因为我只想在用户登录时显示它。我该如何解决这个问题？

Answer 1

试试这个，应该可以。欢迎页面

public class WelcomePage extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.welcome_fragment, container, false);

        //Have tried this one and it works fine
        BottomNavigationView.OnNavigationItemSelectedListener menuListener 
        = new BottomNavigationView.OnNavigationItemSelectedListener() {...}

        BottomNavigationView bottomNav = view.findViewById(R.id.bottomnavigate);
        bottomNav.setOnNavigationItemSelectedListener(menuListener);

        return view;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}

主要活动

   public class MainActivity extends AppCompatActivity {

   private FragmentManager fm;

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

       fm = getSupportFragmentManager();
       Login loggingIn= new Login();
       fm.beginTransaction().replace(R.id.container, loggingIn).commit();
   }

   //When button is pressed we get into this function
   public void finishProcess() {

        WelcomePage wp = new WelcomePage();
        fm.beginTransaction().addToBackStack(null);
        fm.beginTransaction().replace(R.id.container, wp).commit();
    }
}

不同布局中的 findViewById（找不到 BottomNavigationView）

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