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[android] 轮播图-无限循环

2023-02-18 15:46:57 时间

 

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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