学习笔记------viewpager

看到带view的控件基本都避免不了两个要素：适配器和数据源。
其中适配器是每个安卓开发人员最为头疼的东西。适配器怎么使用呢，一般都是要继承Adapter或其子类。今天来讲讲viewpager的使用。

1. 首先布局中加入viewpager控件：

然后在活动中获取控件对象

   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        ViewPager vp=(ViewPager)findViewById(R.id.vp);
        
    }

2. 构造适配器，创建个viewpager继承PagerAdatper，实现其方法。

class viewpageadapter extends PagerAdapter {
        private List views;//layout集合
        public viewpageadapter(List view) {
            this.views = view;
        }

        @Override
        public int getCount() {
            return views.size();//返回layout数量
        }

        @Override
        public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
            return view == object;
        }

        @NonNull
        @Override
        public Object instantiateItem(@NonNull ViewGroup container, int position) {
            container.addView(views.get(position));//直接添加进viewgroup中
            return views.get(position);
        }

        @Override
        public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
            views.remove(views.get(position));
        }


    }

3. 构造数据源
   我们使用三个layout布局作为viewpager数据
   
   在活动中获取三个layout的对象

  private List viewList=new ArrayList<>();//传layout集合给适配器
  LayoutInflater layout = getLayoutInflater().from(this);
    View layout1 = layout.inflate(R.layout.layout1, null);
    View layout2 = layout.inflate(R.layout.layout2, null);
    View layout3 = layout.inflate(R.layout.layout3, null);
    viewList.add(layout1);
    viewList.add(layout2);
    viewList.add(layout3);

4. 将数据放入适配器

 viewpageadapter viewpageadapter=new viewpageadapter(viewList);//创建适配器对象
        vp.setAdapter(viewpageadapter);//viewpager设置适配器

5. 源码

 package com.example.viewpage;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager.widget.PagerAdapter;
import androidx.viewpager.widget.ViewPager;

import android.content.Context;
import android.os.Bundle;
import android.text.Layout;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

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

public class MainActivity extends AppCompatActivity {

    private List viewList=new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        LayoutInflater layout = getLayoutInflater().from(this);
        View layout1 = layout.inflate(R.layout.layout1, null);
        View layout2 = layout.inflate(R.layout.layout2, null);
        View layout3 = layout.inflate(R.layout.layout3, null);
        viewList.add(layout1);
        viewList.add(layout2);
        viewList.add(layout3);

        ViewPager vp=(ViewPager)findViewById(R.id.vp);
        viewpageadapter viewpageadapter=new viewpageadapter(viewList);
        vp.setAdapter(viewpageadapter);
    }
    class viewpageadapter extends PagerAdapter {
        private List views;//layout集合
        public viewpageadapter(List view) {
            this.views = view;
        }

        @Override
        public int getCount() {
            return views.size();//返回layout数量
        }

        @Override
        public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
            return view == object;
        }

        @NonNull
        @Override
        public Object instantiateItem(@NonNull ViewGroup container, int position) {
            container.addView(views.get(position));//直接
            return views.get(position);
        }

        @Override
        public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
             container.removeView(views.get(position));//移除容器内layout
        }


    }
}

示例：