Jump from one Activity to the specified Fragment of another Activity, with the implementation of the bottom menu bar

Implement the bottom menu bar first

This part refers to the B station video Springboot:
2022 latest version] Android Studio installs Android (Android) to develop a zero-based entry to master the full set of tutorials P118-119
renderings:

• I forgot whether to add dependencies. There is a high probability that there is no need to add them, but I still post the possible dependencies first.

    implementation 'androidx.navigation:navigation-fragment:2.3.5'
    implementation 'androidx.navigation:navigation-ui:2.3.5'

• First create a resource file (xml file) of buttom_nav_menu in the menu package under res (if there is no menu package) , the code is:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/bottom_home"
        android:title="@string/bottom_title_home"
        android:icon="@drawable/home"/>
    <item
        android:id="@+id/bottom_notice"
        android:title="@string/bottom_title_notice"
        android:icon="@drawable/notice"
    />
    <item
        android:id="@+id/bottom_mine"
        android:title="@string/bottom_title_mine"
        android:icon="@drawable/person"/>
    <item
        android:id="@+id/bottom_unfold"
        android:title="@string/bottom_title_unfold"
        android:icon="@drawable/more"
        />

</menu>

• Then create four corresponding fragment files based on HomeActivity
• Then the code in HomeActivity

package com.example.academymanageapp.ui;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.content.ClipData;
import android.content.Intent;
import android.os.Bundle;
import android.os.Parcelable;
import android.view.MenuItem;

import com.example.academymanageapp.R;
import com.example.academymanageapp.ui.base.BaseActivity;
import com.example.academymanageapp.ui.home.HomeFragment;
import com.example.academymanageapp.ui.mine.MineFragment;
import com.example.academymanageapp.ui.notice.NoticeFragment;
import com.example.academymanageapp.ui.unfold.UnfoldFragment;
import com.google.android.material.bottomnavigation.BottomNavigationView;

public class HomeActivity extends BaseActivity implements BottomNavigationView.OnNavigationItemSelectedListener {

    private Fragment[] fragments; //fragment数组，用来存储底部菜单栏用到的fragment
    private int lastFragmentIndex = 0;//切换前的fragment
    private int nextFragmentIndex;//切换后的fragment
    private int fragmentFlag;

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

    }

    @Override
    protected void initViews() {

        //初始化fragments
        fragments = new Fragment[]{new HomeFragment(),new NoticeFragment(), new MineFragment(),new UnfoldFragment()};
        //注册一个监听，用来监听用户点击底部菜单里的哪一个fragment
        BottomNavigationView bottomNavigationView = find(R.id.main_bottom_navigation);
        
        //设置默认的
        getSupportFragmentManager().beginTransaction().add(R.id.main_frame,fragments[0]).commit();
    }


    @Override
    protected int getLayoutId() {
        return R.layout.activity_home;
    }

    @Override
    //获得用户点击的menuItem
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
//        item.getItemId();//获得用户点击的部件的Id
        item.setChecked(true);//给点中的item设置checked
        switch (item.getItemId()){
            case R.id.bottom_home:
                switchFragment(0);
                break;
            case R.id.bottom_notice:
                switchFragment(1);
                break;
            case R.id.bottom_mine:
                switchFragment(2);
                break;
            case R.id.bottom_unfold:
                switchFragment(3);
                break;
        }
        return false;
    }

    //默认点击是home，所以要创建一个fragment的切换
    private void switchFragment(int to){
        if (lastFragmentIndex == to){ //如果切换前后一致则不切换
            return;
        }
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        //如果没有添加过,则添加对应的fragment
        if (!fragments[to].isAdded()){
            fragmentTransaction.add(R.id.main_frame,fragments[to]);
        }else {
            fragmentTransaction.show(fragments[to]);//否则就展示出来
        }
        //添加后将之前的隐藏
        fragmentTransaction.hide(fragments[lastFragmentIndex]).commitAllowingStateLoss();
        lastFragmentIndex = to;
    }

}

• The code in the fragment:

package com.example.academymanageapp.ui.mine;

import android.view.View;
import androidx.core.content.ContextCompat;
import com.example.academymanageapp.R;
import com.example.academymanageapp.databinding.FragmentMineBinding;
import com.example.academymanageapp.ui.base.BaseFragment;

public class MineFragment extends BaseFragment {
    private FragmentMineBinding binding;

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        binding = FragmentMineBinding.inflate(inflater, container, false);
        View root = binding.getRoot();
        return root;
        }
        
    @Override
    protected void initViews() {
    }

    @Override
    protected int getLayoutId() {
        return R.layout.fragment_mine;
    }
}

The same goes for other fragments

achieve jump

Reference article: How android jumps from an activity to a fragment specified under another activity

Description of the problem: When completing the design, it is necessary to return from activityA (i.e. ActivityDetailActivity) to the interface before entering (maybe fragmentA (i.e. homeFragment) or fragmentB (i.e. mineFragment) when the return button is clicked. Both belong to HomeActivity).

Idea: When jumping from ActivityDetailActivity, jump with a flag, and jump to the specified fragment according to the flag

The code of the ActivityDetailActivity part:

 Intent intent = new Intent();
 intent.setClass(ActivityDetailActivity.this,HomeActivity.class);
 intent.putExtra("fragment_flag",2);
 startActivity(intent);

The HomeActivity part only needs to make a judgment on the returned value, and switch to the specified fragment according to the value. The added code:

fragmentFlag = getIntent().getIntExtra("fragment_flag",0);
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        switch (fragmentFlag){
            case 0:
                switchFragment(0);
                //使对应的底部菜单栏的Item处于被点击的状态（即点击都更改颜色）
                bottomNavigationView.setSelectedItemId(R.id.bottom_home);
                //调用底部菜单栏函数，以实现根据点击底部菜单栏实现fragment的跳转
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                //记得加break，否则页面不会变化
                break;
            case 1:
                switchFragment(1);
                bottomNavigationView.setSelectedItemId(R.id.bottom_notice);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
            case 2:
                switchFragment(2);
                bottomNavigationView.setSelectedItemId(R.id.bottom_mine);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
            case 3:
                switchFragment(3);
                bottomNavigationView.setSelectedItemId(R.id.bottom_unfold);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
        }
        transaction.commit();

At this point the complete code of HomeActivity is:

package com.example.academymanageapp.ui;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.content.ClipData;
import android.content.Intent;
import android.os.Bundle;
import android.os.Parcelable;
import android.view.MenuItem;

import com.example.academymanageapp.R;
import com.example.academymanageapp.ui.base.BaseActivity;
import com.example.academymanageapp.ui.home.HomeFragment;
import com.example.academymanageapp.ui.mine.MineFragment;
import com.example.academymanageapp.ui.notice.NoticeFragment;
import com.example.academymanageapp.ui.unfold.UnfoldFragment;
import com.google.android.material.bottomnavigation.BottomNavigationView;

public class HomeActivity extends BaseActivity implements BottomNavigationView.OnNavigationItemSelectedListener {

    private Fragment[] fragments; //fragment数组，用来存储底部菜单栏用到的fragment
    private int lastFragmentIndex = 0;//切换前的fragment
    private int nextFragmentIndex;//切换后的fragment
    private int fragmentFlag;

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

    }

    @Override
    protected void initViews() {

        //初始化fragments
        fragments = new Fragment[]{new HomeFragment(),new NoticeFragment(), new MineFragment(),new UnfoldFragment()};
        //注册一个监听，用来监听用户点击底部菜单里的哪一个fragment
        BottomNavigationView bottomNavigationView = find(R.id.main_bottom_navigation);

        fragmentFlag = getIntent().getIntExtra("fragment_flag",0);
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        switch (fragmentFlag){
            case 0:
                switchFragment(0);
                //使对应的底部菜单栏的Item处于被点击的状态（即点击都更改颜色）
                bottomNavigationView.setSelectedItemId(R.id.bottom_home);
                //调用底部菜单栏函数，以实现根据点击底部菜单栏实现fragment的跳转
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                //记得加break，否则页面不会变化
                break;
            case 1:
                switchFragment(1);
                bottomNavigationView.setSelectedItemId(R.id.bottom_notice);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
            case 2:
                switchFragment(2);
                bottomNavigationView.setSelectedItemId(R.id.bottom_mine);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
            case 3:
                switchFragment(3);
                bottomNavigationView.setSelectedItemId(R.id.bottom_unfold);
                bottomNavigationView.setOnNavigationItemSelectedListener(this);
                break;
        }
        transaction.commit();

        //设置默认的
        getSupportFragmentManager().beginTransaction().add(R.id.main_frame,fragments[0]).commit();
    }


    @Override
    protected int getLayoutId() {
        return R.layout.activity_home;
    }

    @Override
    //获得用户点击的menuItem
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
//        item.getItemId();//获得用户点击的部件的Id
        item.setChecked(true);//给点中的item设置checked
        switch (item.getItemId()){
            case R.id.bottom_home:
                switchFragment(0);
                break;
            case R.id.bottom_notice:
                switchFragment(1);
                break;
            case R.id.bottom_mine:
                switchFragment(2);
                break;
            case R.id.bottom_unfold:
                switchFragment(3);
                break;
        }
        return false;
    }

    //默认点击是home，所以要创建一个fragment的切换
    private void switchFragment(int to){
        if (lastFragmentIndex == to){ //如果切换前后一致则不切换
            return;
        }
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        //如果没有添加过,则添加对应的fragment
        if (!fragments[to].isAdded()){
            fragmentTransaction.add(R.id.main_frame,fragments[to]);
        }else {
            fragmentTransaction.show(fragments[to]);//否则就展示出来
        }
        //添加后将之前的隐藏
        fragmentTransaction.hide(fragments[lastFragmentIndex]).commitAllowingStateLoss();
        lastFragmentIndex = to;
    }

}