使用底部导航时出现运行时错误

Question

我是安卓工作室的新手。我需要使用底部导航和不同的fragemnet。当我运行应用程序时，会出现"应用程序停止响应"消息。我找不到这个问题。我有一个运行时错误，上面写着：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: np.com.app.journeyjournal, PID: 28863
java.lang.RuntimeException: Unable to start activity 
ComponentInfo{np.com.app.journeyjournal/np.com.app.journeyjournal.MainActivity}: 
java.lang.IllegalStateException: Activity np.com.app.journeyjournal.MainActivity@33614f5 does 
not have a NavController set on 2131230919

mainactivity.java文件为：

package np.com.app.journeyjournal;
import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.NavigationUI;

import android.os.Bundle;

import com.google.android.material.bottomnavigation.BottomNavigationView;

public class MainActivity extends AppCompatActivity {


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


NavController navController;
BottomNavigationView bottomNavigationView;
bottomNavigationView = findViewById(R.id.bottomNavigationView);
navController = Navigation.findNavController(this,  R.id.fragment);

NavigationUI.setupWithNavController(bottomNavigationView,navController);

}
}

Answer 1

您是否在xml文件中添加了NavHostFragment？

<fragment
android:id="@+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="@navigation/nav_graph" />