這回寫的是，實現ViewPager底部切換

我寫的這是，點選為true，和為false的兩種顯示，首先在drawable建一個對應的檔案

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

主佈局檔案

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

  
    <androidx.viewpager.widget.ViewPager
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_weight="9"
        android:id="@+id/view_pager"
        />
    <RadioGroup
        android:layout_width="match_parent"
        android:layout_height="75dp"
        android:background="#FFFFF0"
        android:orientation="horizontal"
        android:id="@+id/rg"
        >
        <RadioButton
            android:id="@+id/shouye"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="首頁"
            android:padding="5dp"
            android:button="@null"
            android:gravity="center"
            android:checked="true"
            android:drawableTop="@drawable/shouye"/>
        <RadioButton
            android:id="@+id/dingdan"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="訂單"
            android:padding="5dp"
            android:button="@null"
            android:gravity="center"
            android:drawableTop="@drawable/dingdan"/>
        <RadioButton
            android:id="@+id/wode"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="我的"
            android:padding="5dp"
            android:button="@null"
            android:gravity="center"
            android:drawableTop="@drawable/wode"/>
    </RadioGroup>

</LinearLayout>
 

這個是MainActivity裡的程式碼

package com.example.administrator.myapplication;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.viewpager.widget.ViewPager;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;

import com.example.administrator.myapplication.Fragment.DingDanActivity;
import com.example.administrator.myapplication.Fragment.ShouYieActivity;
import com.example.administrator.myapplication.Fragment.WoDeActivity;


import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    private ViewPager view_pager;
    private RadioButton shouye;
    private RadioButton dingdan;
    private RadioButton wode;
    private RadioGroup rg;
    private ArrayList<Fragment> list;



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

        init();
        setOnListener();
        list = new ArrayList<>();
        list.add(new ShouYieActivity());
        list.add(new DingDanActivity());
        list.add(new WoDeActivity());
        view_pager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {
            @Override
            public Fragment getItem(int i) {
                return list.get(i);
            }

            @Override
            public int getCount() {
                return list.size();
            }
        });
    }

    private void setOnListener() {
        view_pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                switch (position){
                    case 0:
                        rg.check(R.id.shouye);
                        break;
                    case 1:
                        rg.check(R.id.dingdan);
                        break;
                    case 2:
                        rg.check(R.id.wode);
                        break;
                }

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        rg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup radioGroup, int i) {
                switch (i){
                    case R.id.shouye:
                        view_pager.setCurrentItem(0);
                        break;
                    case R.id.dingdan:
                        view_pager.setCurrentItem(1);
                        break;
                    case R.id.wode:
                        view_pager.setCurrentItem(2);
                        break;
                }
            }
        });
    }

    private void init() {
         view_pager = findViewById(R.id.view_pager);
         shouye = findViewById(R.id.shouye);
         dingdan = findViewById(R.id.dingdan);
         wode = findViewById(R.id.wode);
         rg = findViewById(R.id.rg);


    }

}
 

我也沒標，註解，但是每個方法的意思都很簡單，上網上查一下就好