Android 导航问题如果我有多个底部导航视图怎么办

您好，我在实现这一点时遇到了很多问题。我在主要活动中有以下xml

主要内容

    <LinearLayout 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"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:context=".MainActivity"
        android:orientation="vertical"
        tools:showIn="@layout/app_bar_main">

      <fragment
            android:id="@+id/nav_host"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:name="androidx.navigation.fragment.NavHostFragment"
            app:navGraph="@navigation/bottom_nav_usuario_auto"
            app:defaultNavHost="true"
            android:layout_weight="6">

        </fragment>

        <FrameLayout
            android:id="@+id/bottom_nav_container"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="0.8"
           />

    </LinearLayout>

这是底部配置和

fragment\u Bottom\u nav\u usuario\u auto

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".BottomNavUsuarioAuto">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">


    <!-- TODO: Update blank fragment layout -->
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_nav_switcher"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:menu="@menu/nav_usuario_auto"
        android:layout_gravity="start"
        android:text="@string/hello_blank_fragment" />
    </LinearLayout>

</FrameLayout>

我在这个过程中看到了两种类型的错误

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.franco.mac.jetpacknavigation2/com.franco.mac.jetpacknavigation2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation.BottomNavigationView.setOnNavigationItemSelectedListener(com.google.android.material.bottomnavigation.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference

以及：

---

如果你现在不知道答案，请不要回答。我想知道完成此练习的正确方法。

代码不完整。也许当你调用

BottomNavigationView-BottomNavigationView=findViewById（R.id.bottom\u nav\u switcher）

时，没有视图，

BottomNavigationView

为

null

。你好，Gabriele，我注释掉了代码，最终在frameLayout中得到了一个视图，所以情况并非如此。这取决于调用代码的位置以及片段是否刚刚初始化。

<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:title="Inicio"
        android:id="@+id/fragmento_a_usuario_auto"
        android:icon="@drawable/ic_menu_camera"
        android:iconTint="#FF9800"
        />
    <item android:title="Mi carro"
        android:icon="@drawable/ic_menu_manage"
        android:id="@+id/fragmento_b_usuario_auto"
        android:iconTint="#FF9800"
        />
    <item android:title="Comercial"
        android:id="@+id/fragmento_c_usuario_auto"
        android:icon="@drawable/ic_menu_send"
        android:iconTint="#FF9800"
        />
    <item
        android:title="Cita taller"
        android:id="@+id/fragmento_d_usuario_auto"
        android:icon="@drawable/ic_menu_share"
        android:iconTint="#FF9800"

        />
</menu>

NavController navController= Navigation.findNavController(this,R.id.nav_host);
BottomNavigationView bottomNavigationView=findViewById(R.id.bottom_nav_switcher);           
NavigationUI.setupWithNavController(bottomNavigationView,navController);

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.franco.mac.jetpacknavigation2/com.franco.mac.jetpacknavigation2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation.BottomNavigationView.setOnNavigationItemSelectedListener(com.google.android.material.bottomnavigation.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference

  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.franco.mac.jetpacknavigationexample/com.franco.mac.jetpacknavigationexample.MainActivity}: android.view.InflateException: `Binary XML file line #11: Binary XML file line #12: Error inflating class fragment`