Android实现底部导航菜单的跳转--BottomNavigationView

效果：

项目结构：



需要用到design依赖： 现在是：implementation ‘com.android.support:design:28.0.0’
代码：
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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">
    <FrameLayout
        android:id="@+id/frame_fragment"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@id/bottomNavigationView"/>
    <android.support.design.widget.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:itemBackground="@color/white"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHeight_percent="0.09"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:itemIconTint="@drawable/home_bottom_tab_color_selsctor"
        app:itemTextColor="@drawable/home_bottom_tab_color_selsctor"
        app:menu="@menu/bottom_navigation_main" />
</android.support.constraint.ConstraintLayout>

my_fragment.xml(其他两个类似不在累述)

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    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="fill_parent"
    android:layout_height="fill_parent">

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:text="我的界面"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints" />
</android.support.constraint.ConstraintLayout>

home_bottom_tab_color_selsctor.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:color="@color/black" android:state_checked="false" />
    <item android:color="@color/home_bottom_tab_blue" android:state_checked="true" />
</selector>

home_bottom_tab_my_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:state_checked="false"
        android:drawable="@drawable/home_bottom_tab_icon_my_normal"
       />
    <item
        android:state_checked="true"
        android:drawable="@drawable/home_bottom_tab_icon_my_highlight"
      />
</selector>

MainActivity

import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.MenuItem;
import android.widget.FrameLayout;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {


    private  BottomNavigationView bottomNavigationView;
    private Fragment work_fragment;
    private Fragment message_fragment;
    private Fragment my_fragment;
    private Fragment[] fragments;
    private int lastfragment;//用于记录上个选择的Fragment

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

        initFragment();
    }

    private void initFragment() {
        work_fragment = new Work_Fragment();
        message_fragment = new Message_Fragment();
        my_fragment = new My_Fragment();
        fragments = new Fragment[]{message_fragment, work_fragment, my_fragment};
        lastfragment = 0;
        getSupportFragmentManager().beginTransaction().replace(R.id.frame_fragment, message_fragment).show(message_fragment).commit();
        bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottomNavigationView);

        bottomNavigationView.setOnNavigationItemSelectedListener(changeFragment);
    }
    private BottomNavigationView.OnNavigationItemSelectedListener changeFragment = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {

            switch (item.getItemId()) {
                case R.id.action_message: {
                    if (lastfragment != 0) {
                        switchFragment(lastfragment, 0);
                        lastfragment = 0;
                    }
                    return true;
                }
                case R.id.action_work: {
                    if (lastfragment != 1) {
                        switchFragment(lastfragment, 1);
                        lastfragment = 1;

                    }

                    return true;
                }
                case R.id.action_my: {
                    if (lastfragment != 2) {
                        switchFragment(lastfragment, 2);
                        lastfragment = 2;
                    }
                    return true;
                }
            }
            return false;
        }
    };


    //切换Fragment
    private void switchFragment(int lastfragment, int index) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.hide(fragments[lastfragment]);//隐藏上个Fragment
        if (fragments[index].isAdded() == false) {
            transaction.add(R.id.frame_fragment, fragments[index]);
        }
        transaction.show(fragments[index]).commitAllowingStateLoss();

    }



 /*   public boolean onKeyUp(int keyCode, KeyEvent event) {
        //在主界面，连击连两下退出程序
        if(keyCode==KeyEvent.KEYCODE_BACK){
            long secondTime=System.currentTimeMillis();
            if(secondTime-firstTime>800){
                Toast.makeText(Home_Activity.this,"再按一次返回键退出",Toast.LENGTH_SHORT).show();
                firstTime=secondTime;
                return true;
            }else{
                WelcomeActivity.activity.finish();
                System.exit(0);
            }
        }
        return super.onKeyUp(keyCode, event);
    }*/
}

My_fragment(其他两个类似不在累述)

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class My_Fragment extends Fragment {
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.my_fragment,null);

        return view;
    }
}

全部代码：https://github.com/EternalMsc/BottomNavigationView