• 底部导航栏是基于Bottom Navigation Bar 插件使用的
• 这个插件包裹在com.android.support:design:28.0.0，必须引入

1. 设计底部导航栏页面

1.1. 创建必须的文件夹

• 在res下创建color和menu文件夹

color文件夹： 用于存放导航栏的个性化颜色

menu文件夹： 用于存放导航栏的子项

1.2. 设计主页面

• 首先设计子项: menu下新建nav_items.xml文件

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

    <item
        android:id="@+id/nav_homes"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/nav_home" />
    <item
        android:id="@+id/nav_searchs"
        android:icon="@drawable/ic_search_black_24dp"
        android:title="@string/nav_search" />
    <item
        android:id="@+id/nav_accounts"
        android:icon="@drawable/ic_account_circle_black_24dp"
        android:title="@string/nav_account" />
</menu>

• 设计个性化颜色，color文件夹下新建nav_item_color.xml

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

• 然后再主页面中引入子项 ，在activity_main.xml写

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    tools:context=".MainActivity">

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/main_nav"
        android:layout_width="match_parent"
        android:layout_height="56dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentBottom="true"
        app:itemBackground="@color/colorPrimary"
        app:itemIconTint="@color/nav_item_color"
        app:itemTextColor="@color/nav_item_color"
        app:menu="@menu/nav_items"></android.support.design.widget.BottomNavigationView>

    <FrameLayout
        android:id="@+id/main_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@+id/main_nav">

    </FrameLayout>

</RelativeLayout>

2. 设计逻辑函数

点击每个子项都可以跳转到对应的页面上去

• 首先创建三个fragment： MainFragment, SearchFragment, AccountFragment
  
• 然后再主页面中写逻辑函数

package com.example.myapplication;

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.MenuItem;
import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity {

    private BottomNavigationView mMainNav;
    private FrameLayout mMainFrame;
    private HomeFragment homeFragment;
    private SearchFragment searchFragment;
    private AccountFragment accountFragment;

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

        mMainFrame = (FrameLayout)findViewById(R.id.main_frame);
        mMainNav = (BottomNavigationView)findViewById(R.id.main_nav);

        homeFragment = new HomeFragment();
        searchFragment = new SearchFragment();
        accountFragment = new AccountFragment();

        // 设置默认的fragment
        setFragment(homeFragment);

        mMainNav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {


                switch (menuItem.getItemId()){
                    case R.id.nav_homes:
                        setFragment(homeFragment);
                        return true;
                    case R.id.nav_searchs:
                        setFragment(searchFragment);
                        return true;
                    case R.id.nav_accounts:
                        setFragment(accountFragment);
                        return true;
                    default:
                        return false;
                }
            }
        });
    }

//    根据传入的framgment对象，对现在设置新的fragment
    private void setFragment(Fragment fragment) {

        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();

        fragmentTransaction.replace(R.id.main_frame, fragment);

        fragmentTransaction.commit();

    }
}

3. 项目展示

Android应用-底部导航栏的使用