Android導航欄

** 原始碼**

Android Studio匯入Android專案需要洗掉的檔案
1、.idea檔案夾
2、.gradle檔案夾
3、所有的build檔案夾
4、所有的.iml檔案
5、local.properties檔案，

廢話不多說，直接上代碼

java代碼

Mainactivity

package com.example.ex04;//修改為自己的包名


import android.os.Bundle;
import android.view.MenuItem;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;

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

public class MainActivity extends AppCompatActivity {

    private BottomNavigationView navigationView;

    //創建四個Fragment和存放他們的陣列
    private Fragment Fragment1;
    private Fragment Fragment2;
    private Fragment Fragment3;
    private Fragment Fragment4;
    public Fragment[] fragmentlist;

    //用于標識上一個fragment
    private int lastFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //fragment初始化
        initFragment();
    }

    /**
     * 初始化fragment，并將Fragment1顯示出來
     */
    private void initFragment() {
        navigationView = findViewById(R.id.bnv_main);
        //配置選單按鈕顯示圖示
        navigationView.setItemIconTintList(null);
        //將三個fragment先放在陣列里
        Fragment1 = new Fragment1();
        Fragment2 = new Fragment2();
        Fragment3 = new Fragment3();
        Fragment4 = new Fragment4();
        fragmentlist = new Fragment[]{Fragment1, Fragment2, Fragment3, Fragment4};
        lastFragment = 0;
        //為navigationView設定點擊事件
        navigationView.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

        //設定默認頁面為Fragment1
        getSupportFragmentManager().beginTransaction().replace(R.id.fl_main, Fragment1)
                .show(Fragment1).commit();
        navigationView.setSelectedItemId(R.id.navigation_home);
    }

    /**
     * 給BottomNavigationView添加按鈕的點擊事件
     */
    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            //每次點擊后都將所有圖示重置到默認不選中圖片
            resetToDefaultIcon();

            switch (item.getItemId()) {
                case R.id.navigation_home:
                    //判斷要跳轉的頁面是否是當前頁面，若是則不做動作
                    if (lastFragment != 0) {
                        switchFragment(lastFragment, 0);
                        lastFragment = 0;
                    }
                    //設定按鈕
                    item.setIcon(R.drawable.homea);
                    return true;
                case R.id.navigation_buy:
                    if (lastFragment != 1) {
                        switchFragment(lastFragment, 1);
                        lastFragment = 1;
                    }
                    item.setIcon(R.drawable.shopa);
                    return true;
                case R.id.navigation_user:
                    if (lastFragment != 2) {
                        switchFragment(lastFragment, 2);
                        lastFragment = 2;
                    }
                    item.setIcon(R.drawable.usera);
                    return true;
                case R.id.navigation_love:
                    if (lastFragment != 3) {
                        switchFragment(lastFragment, 3);
                        lastFragment = 3;
                    }
                    item.setIcon(R.drawable.lovea);
                    return true;
            }
            return false;
        }
    };

    /**
     * @param lastFragment 表示點擊按鈕前的頁面
     * @param index        表示點擊按鈕對應的頁面
     */
    private void switchFragment(int lastFragment, int index) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        //隱藏上個Fragment
        transaction.hide(fragmentlist[lastFragment]);

        //判斷transaction中是否加載過index對應的頁面，若沒加載過則加載
        if (fragmentlist[index].isAdded() == false) {
            transaction.add(R.id.fl_main, fragmentlist[index]);
        }
        //根據角標將fragment顯示出來
        transaction.show(fragmentlist[index]).commitAllowingStateLoss();
    }


    /**
     * 重新配置每個按鈕的圖示
     */
    private void resetToDefaultIcon() {
        navigationView.getMenu().findItem(R.id.navigation_home).setIcon(R.drawable.homeb);
        navigationView.getMenu().findItem(R.id.navigation_buy).setIcon(R.drawable.shopb);
        navigationView.getMenu().findItem(R.id.navigation_love).setIcon(R.drawable.loveb);
        navigationView.getMenu().findItem(R.id.navigation_user).setIcon(R.drawable.userb);
    }

}

創建四個布局檔案和java檔案
Fragment1.java + fragment_head.xml
Fragment2.java + fragment_order.xml
Fragment3.java + fragment_love.xml
Fragment4.java + fragment_user.xml
這里我就貼出來其中的一個，其他Java代碼和相應的布局檔案都是一樣的，修改修改就行了

Fragment1.java

package com.example.ex04;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

public class Fragment1 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //該View表示該碎片的主界面,最后要回傳該view
        View view=inflater.inflate(R.layout.fragment_head,container,false);
        //fragment_head為對應的布局檔案
      
        //注意：因為主界面現在是view，所以在找尋控制元件時要用view.findViewById
        
        TextView textView=view.findViewById(R.id.tv1);
       //tv1為對應的布局檔案文本框名
       
        return view;
    }
}

fragment_head.xml

 <ScrollView  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">

 <TextView
     android:id="@+id/tv1"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_centerInParent="true"
     android:text="我是首頁"
     android:textSize="30dp" />

 </ScrollView >

還有一個activity_main.xml檔案

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:orientation="vertical"
    tools:context="com.example.ex04.MainActivity">

    <!--用于切換fragment-->
    <FrameLayout
        android:id="@+id/fl_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/bnv_main"/>

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bnv_main"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        app:menu="@menu/navigation"/>
</RelativeLayout>

在res下新建一個menu檔案夾navigation.xml

最后別忘在AndroidManifest.xml里面注冊活動，我把相應的代碼貼出來僅供參考

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ex04">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
             <!--活動的注冊--> 
        <activity android:name=".Fragment1"></activity>
        <activity android:name=".Fragment2"></activity>
        <activity android:name=".Fragment3"></activity>
        <activity android:name=".Fragment4"></activity>
    </application>

</manifest>

最后還有需要的圖片