（安卓初步）简单的ViewPager加小圆点实现引导页效果

实现

XML主布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        app:layout_constraintBottom_toBottomOf="@+id/viewPager"
        app:layout_constraintEnd_toEndOf="@+id/viewPager"
        app:layout_constraintStart_toStartOf="@+id/viewPager"
        app:layout_constraintTop_toTopOf="@+id/viewPager"
        app:layout_constraintVertical_bias="0.86">

        <ImageView
            android:id="@+id/dot_1"
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:layout_marginRight="5dp"
            />

        <ImageView
            android:id="@+id/dot_2"
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:layout_margin="5dp"
            />

        <ImageView
            android:id="@+id/dot_3"
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:layout_marginLeft="5dp"
            />
    </LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

主要布局为Viewpager 和里面的LinearLayout中的ImageView，用RelativeLayout亦可；

准备3个View

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="100dp"
        android:gravity="center_horizontal"
        android:text="--1--"
        android:textSize="34sp" />
</LinearLayout>

只有text里的文字不同

PagerAdapter

package com.aaa_xcdq.cthreeday;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;

import java.util.List;

public class MyPagerAdapter extends PagerAdapter {
    private List<View> views;
    private Context context;

    public MyPagerAdapter(List<View> views, Context context) {
        this.views = views;
        this.context = context;
    }

   //获得viewpager中有多少个view
    @Override
    public int getCount() {
        return views.size();
    }

    //判断instantiateItem(ViewGroup, int)函数所返回来的Key与一个页面视图是否是 代表的同一个视图
    // (即它俩是否是对应的，对应的表示同一个View),通常我们直接写 return view == object!
    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view==object;
    }

    //①将给定位置的view添加到ViewGroup(容器)中,创建并显示出来 ②返回一个代表新增页面的Object(key),
    // 通常都是直接返回view本身就可以了,当然你也可以 自定义自己的key,但是key和每个view要一一对应的关系
    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        container.addView(views.get(position));
        return views.get(position);
    }

    //移除一个给定位置的页面
    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView(views.get(position));
    }
}

主Activity

package com.aaa_xcdq.cthreeday;

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

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ViewPager viewPager;
    private List<View> views;
    private MyPagerAdapter pagerAdapter;
    private ImageView dot1,dot2,dot3;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager=findViewById(R.id.viewPager);
        initView();
    }

    private void initView() {
        //每个小点
        dot1=findViewById(R.id.dot_1);
        dot2=findViewById(R.id.dot_2);
        dot3=findViewById(R.id.dot_3);
        //把第一个设置亮其他为暗
        setDot(true,false,false);
        
        //得到view数据
        views=new ArrayList<>();
        LayoutInflater inflater=getLayoutInflater();
        views.add(inflater.inflate(R.layout.view_1,null,false));
        views.add(inflater.inflate(R.layout.view_2,null,false));
        views.add(inflater.inflate(R.layout.view_3,null,false));
        //创建Adapter
        pagerAdapter=new MyPagerAdapter(views,this);
        viewPager.setAdapter(pagerAdapter);
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            
            //当页面滑动时
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            //当页面选中时
            @Override
            public void onPageSelected(int position) {

                switch (position){
                    case 0:
                        setDot(true,false,false);
                        break;
                    case 1:
                        setDot(false,true,false);
                        break;
                    case 2:
                        setDot(false,false,true);
                        break;
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }
    
    //小点的变化方法，为true时背景设亮，为false时背景设暗
    private void setDot(boolean a,boolean b,boolean c){
        if (a){
            dot1.setBackgroundResource(R.drawable.point_on);
        }else {
            dot1.setBackgroundResource(R.drawable.point_off);
        }

        if (b){
            dot2.setBackgroundResource(R.drawable.point_on);
        }else {
            dot2.setBackgroundResource(R.drawable.point_off);
        }

        if (c){
            dot3.setBackgroundResource(R.drawable.point_on);
        }else {
            dot3.setBackgroundResource(R.drawable.point_off);
        }
    }
}