ViewPager

ViewPager是google SDk中自带的一个附加包的一个类，可以用来实现屏幕间的切换

今天要讲的是用ViewPager实现图片的自动轮播，也可以用此控件加载页面，我前面有写过此案例，感兴趣的人可以去看看。好了，开始今天的学习；

Activity中

package com.example.viewpager;
//导包
import android.app.Activity;
import android.app.ListActivity;
import android.os.Handler;
import android.os.Message;
import android.support.v4.view.ViewPager;

import android.os.Bundle;

import android.widget.RadioGroup;

import java.util.ArrayList;
import java.util.List;
//类
public class MainActivity extends Activity {
ViewPager viewPager;
    int i = 0;
//主线程更改UI
 Handler h = new Handler(){
        @Override
        public void handleMessage(Message msg) {
//接受发过来的消息，改变数据位置
 if(msg.what==0){
                i = viewPager.getCurrentItem();
                viewPager.setCurrentItem(i+1);
            }
        }
    };
    private List<Integer> list;
    private RadioGroup radio;
    private Myadper myadper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//加载布局
        setContentView(R.layout.activity_main);
//获取资源id
        radio = (RadioGroup) findViewById(R.id.radio);
        viewPager = (ViewPager) findViewById(R.id.viewpager);
//定义一个集合，把数据放入集合
        list = new ArrayList<Integer>();
 //图片放入res文件下的mipmap-xxx下  
        list.add(R.mipmap.a1);
        list.add(R.mipmap.a2);
        list.add(R.mipmap.a3);
        list.add(R.mipmap.a4);


//适配器，适配数据
        myadper = new Myadper(list,this);
        viewPager.setAdapter(myadper);
//图片自动轮播跟着的小圆点的设置
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                switch (position% list.size()){
                    case 0:
                        radio.check(R.id.b1);
                        break;
                    case 1:
                        radio.check(R.id.b2);
                        break;
                    case 2:
                        radio.check(R.id.b3);
                        break;
                    case 3:
                        radio.check(R.id.b4);
                        break;
                }
            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
//定义个子线程，两秒发送消息，主线程去更改UI
        new Thread(){
            @Override
            public void run() {
                try {
                    while(true){

                    sleep(2000);
                    h.sendEmptyMessage(0);
                   }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

适配器

package com.example.viewpager;

import android.content.Context;

import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView

import java.util.List;


//类继承PagerAdapter,实现四个方法
public class Myadper extends PagerAdapter{

 //通过构造器传递数据

 List<Integer> list;
    Context context;

    public Myadper(List<Integer> list, Context context) {
        this.list = list;
        this.context = context;
    }
//返回一个最大值
    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }
//创建
    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView image = new ImageView(context);
        image.setImageResource(list.get(position%list.size()));
        image.setScaleType(ImageView.ScaleType.FIT_XY);
        container.addView(image);
        return image;
    }
//销毁
    @Override
        public void destroyItem(ViewGroup container, int position, Object object) {

        container.removeView((View) object);
    }
}

XML文件

<?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:id="@+id/activity_main"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.viewpager.MainActivity">

  <android.support.v4.view.ViewPager
      android:id="@+id/viewpager"
      android:layout_height="match_parent"
      android:layout_width="match_parent"
      />

    <RadioGroup
        android:id="@+id/radio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:orientation="horizontal">
        <RadioButton
            android:id="@+id/b1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />
        <RadioButton
            android:id="@+id/b2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />
        <RadioButton
            android:id="@+id/b3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />
        <RadioButton
            android:id="@+id/b4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />
    </RadioGroup>
</RelativeLayout>

实现的案例效果