Android轮播图无限循环 Android实现轮播图无限循环效果

时间:2021-03-24 陶士涵人气:0

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实现无限循环

在getCount()方法中，返回一个很大的值，Integer.MAX_VALUE

在instantiateItem()方法中，获取当前View的索引时，进行取于操作，传递进来的int position是个非常大的数，对他进行求余数

在destroyItem()方法中，同样

在onPageSelected()监听方法中，对传递进来的索引进行取于

反向的无限循环

调用ViewPager对象的setCurrentItem()方法，设置第一次进来时候的当前页，参数：int数字，我们把它定位到Integer.MAX_VALUE的中间，并且保证第一条是当前位置，Integer.MAX_VALUE/2-((Integer.MAX_VALUE/2)%banners.size())

目前有个左划空白页的问题没解决

package com.tsh.myviewpager;

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

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends Activity {
  private ViewPager vp_banner;
  private LinearLayout ll_points;
  private TextView tv_title;
  private List<View> banners;
  private String[] titles=new String[]{
      "新闻标题1",
      "新闻标题2",
      "新闻标题3"
  };
  private List<ImageView> points=new ArrayList<ImageView>();
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 初始化
    vp_banner = (ViewPager) findViewById(R.id.vp_banner);
    ll_points = (LinearLayout) findViewById(R.id.ll_points);
    tv_title = (TextView) findViewById(R.id.tv_title);
    
    // banner部分
    banners = new ArrayList<>();
    ImageView img1 = new ImageView(this);
    img1.setImageResource(R.drawable.a);
    banners.add(img1);
    ImageView img2 = new ImageView(this);
    img2.setImageResource(R.drawable.b);
    banners.add(img2);
    ImageView img3 = new ImageView(this);
    img3.setImageResource(R.drawable.c);
    banners.add(img3);
    
    //小图标
    ll_points=(LinearLayout) findViewById(R.id.ll_points);
    for(int i=0;i<banners.size();i++){
      ImageView image=new ImageView(this);
      image.setImageResource(R.drawable.point_selector);
      LinearLayout.LayoutParams params=new LinearLayout.LayoutParams(5, 5);
      params.rightMargin=4;
      image.setLayoutParams(params);
      
      if(i==0){
        image.setEnabled(true);
      }else{
        image.setEnabled(false);
      }
      points.add(image);
      ll_points.addView(image);
    }
    
    // 设置适配器
    vp_banner.setAdapter(new MyPagerAdapter());
    vp_banner.setCurrentItem(Integer.MAX_VALUE/2-((Integer.MAX_VALUE/2)%banners.size()));
    vp_banner.setOnPageChangeListener(new OnPageChangeListener() {
      @Override
      public void onPageSelected(int arg0) {
        tv_title.setText(titles[arg0%banners.size()]);
        //小图标处理
        for(ImageView point:points){
          point.setEnabled(false);
        }
        points.get(arg0%banners.size()).setEnabled(true);
      }
      
      @Override
      public void onPageScrolled(int arg0, float arg1, int arg2) {
        // TODO Auto-generated method stub
        
      }
      
      @Override
      public void onPageScrollStateChanged(int arg0) {
        // TODO Auto-generated method stub
        
      }
    });
    
  }

  private class MyPagerAdapter extends PagerAdapter {
    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
      System.out.println("销毁："+position);
      container.removeView((View)object);
      object=null;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
      System.out.println("初始化："+position);
      position=position%banners.size();
      
      //解决右划出错
      if(banners.get(position).getParent()!=null){
        //container.removeView(banners.get(position));
      }else{
        container.addView(banners.get(position));
      }
      
      return banners.get(position);
    }

    @Override
    public int getCount() {
      return Integer.MAX_VALUE;
    }

    @Override
    public boolean isViewFromObject(View arg0, Object arg1) {
      return arg0 == arg1;
    }
  }
}

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