package com.example.navigation;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import androidx.navigation.NavController;

import androidx.navigation.Navigation;

import androidx.navigation.ui.NavigationUI;

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

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

        NavigationUI.setupActionBarWithNavController(this,navController);

    }

    @Override

    public boolean onSupportNavigateUp() {

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

        return navController.navigateUp();

    }

}

package com.example.navigation;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v4.app.Fragment;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Button;

import androidx.navigation.NavAction;

import androidx.navigation.NavController;

import androidx.navigation.Navigation;

/**

 * A simple {@link Fragment} subclass.

 */

public class Home_Fragment extends Fragment {

    public Home_Fragment() {

        // Required empty public constructor

    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        return inflater.inflate(R.layout.fragment_home_, container, false);

    }

    @Override

    public void onActivityCreated(@Nullable Bundle savedInstanceState) {

        super.onActivityCreated(savedInstanceState);

        Button button = getView().findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                NavController navController = Navigation.findNavController(v);

                navController.navigate(R.id.action_home_Fragment_to_detail_Fragment);

            }

        });

    }

}

package com.example.navigation;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v4.app.Fragment;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Button;

import androidx.navigation.NavController;

import androidx.navigation.Navigation;

/**

 * A simple {@link Fragment} subclass.

 */

public class Detail_Fragment extends Fragment {

    public Detail_Fragment() {

        // Required empty public constructor

    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        return inflater.inflate(R.layout.fragment_detail_, container, false);

    }

    @Override

    public void onActivityCreated(@Nullable Bundle savedInstanceState) {

        super.onActivityCreated(savedInstanceState);

//        Button button = getView().findViewById(R.id.button2);

//        button.setOnClickListener(new View.OnClickListener() {

//            @Override

//            public void onClick(View v) {

//                NavController navController = Navigation.findNavController(v);

//                navController.navigate(R.id.action_detail_Fragment_to_home_Fragment);

//            }

//        });

        getView().findViewById(R.id.button2).setOnClickListener(Navigation.createNavigateOnClickListener(R.id.action_detail_Fragment_to_home_Fragment));//上方注释的整体写法，功能一样

    }

}