Android uses ViewPager to realize left and right infinite sliding

Preface

There are a lot of data about using ViewPager to realize the effect of sliding left and right on the Internet. Most of these data set the return value of getCount () method in PagerAdapter to Integer. MAX_VALUE so that users can't see the boundary, and then get the corresponding data set in instantiateItem () method by position% (the length of the data set to be displayed cyclically). Although this can achieve infinite loop, but there will be two drawbacks: first, it will create a large number of objects, which will easily cause memory overflow (loop loading pictures) and affect performance; Secondly, when you slide to the right from page 1, you can't slide.

What I want to share with you today is another implementation method: Create three picture views and put them into ViewPager to select Page 2 by default. After each slide in the next slide, set the current page number to Page 2, and then set the data set in the view by judging whether it is sliding left to right, so that an infinite loop can be realized, and only three picture view objects will be created.

Sample source code

package com.viewpager; 
 
import java.util.ArrayList; 
import java.util.List; 
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.app.Activity; 
 
public class MainActivity01 extends Activity implements OnPageChangeListener { 
 
 private ViewPager viewPager; 
 static final int arrays[] = { R.drawable.guide1, R.drawable.guide2, 
   R.drawable.guide3, R.drawable.guide4, R.drawable.guide5 }; 
 private List<ImageView> views; 
 private int currentPage = 0; 
 private ImageView imageView; 
 
 private MyViewPagerAdapter viewPagerAdapter; 
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_main); 
  initWidget(); 
 } 
 
 private void initWidget() { 
  viewPager = (ViewPager) findViewById(R.id.viewpager); 
 
  views = new ArrayList<ImageView>(); 
  for (int i = 0; i < 3; i++) { 
   imageView = new ImageView(this); 
   imageView.setLayoutParams(new ViewGroup.LayoutParams( 
     ViewGroup.LayoutParams.MATCH_PARENT, 
     ViewGroup.LayoutParams.MATCH_PARENT)); 
   views.add(imageView); 
  } 
 
  initImageData(); 
 
  viewPagerAdapter = new MyViewPagerAdapter(); 
  viewPager.setAdapter(viewPagerAdapter); 
  viewPager.setCurrentItem(1); 
  viewPager.setOnPageChangeListener(this); 
 } 
 
 private void initImageData() { 
  for (int i = 0; i < 3; i++) { 
   imageView = views.get(i); 
   if (i == 0) { 
    imageView.setImageResource(arrays[arrays.length - 1]); 
   } else { 
    imageView.setImageResource(arrays[i - 1]); 
   } 
  } 
 } 
 
 class MyViewPagerAdapter extends PagerAdapter { 
 
  @Override 
  public int getCount() { 
   // TODO Auto-generated method stub 
   return views.size(); 
  } 
 
  @Override 
  public boolean isViewFromObject(View arg0, Object arg1) { 
   // TODO Auto-generated method stub 
   return arg0 == arg1; 
  } 
 
  @Override 
  public Object instantiateItem(ViewGroup container, int position) { 
   imageView = views.get(position); 
   container.addView(imageView); 
   return imageView; 
  } 
 
  @Override 
  public void destroyItem(ViewGroup container, int position, Object object) { 
   // TODO Auto-generated method stub 
   container.removeView((View) object); 
  } 
 
 } 
 
 //  Called when the sliding state changes  
 @Override 
 public void onPageScrollStateChanged(int state) { 
  // TODO Auto-generated method stub 
  System.out.println("--onPageScrollStateChanged--state--:" + state); 
  switch (state) { 
  //  After scrolling is completed,  
  case ViewPager.SCROLL_STATE_IDLE: 
   int currentItem = viewPager.getCurrentItem(); 
 
   System.out.println("--currentItem--00--:" + currentItem); 
   System.out.println("--currentPage--00--:" + currentPage); 
   if (viewPager.getCurrentItem() == 1) { 
    //  If the position does not change, terminate the loop  
    break; 
   } 
 
   if (viewPager.getCurrentItem() > 1) { 
    currentPage++; 
   } else { 
    currentPage--; 
   } 
 
   System.out.println("--currentPage--11--:" + currentPage); 
   if (currentPage == arrays.length) { 
    currentPage = 0; 
   } 
 
   if (currentPage == -1) { 
    currentPage = arrays.length - 1; 
   } 
 
   System.out.println("--currentPage--22--:" + currentPage); 
 
   if (currentPage == 0) { 
    views.get(0).setImageResource(arrays[arrays.length - 1]); 
   } else { 
    views.get(0).setImageResource(arrays[currentPage - 1]); 
   } 
 
   views.get(1).setImageResource(arrays[currentPage]); 
 
   if (currentPage == arrays.length - 1) { 
    views.get(2).setImageResource(arrays[0]); 
   } else { 
    views.get(2).setImageResource(arrays[currentPage + 1]); 
   } 
 
   viewPager.setCurrentItem(1, false); 
 
   currentItem = viewPager.getCurrentItem(); 
 
   System.out.println("--currentItem--11--:" + currentItem); 
   break; 
  } 
 } 
 
 //  Called when the current page is slid  
 @Override 
 public void onPageScrolled(int position, float positionOffset, 
   int positionOffsetPixels) { 
  // TODO Auto-generated method stub 
  // System.out.println("--onPageScrolled--position--:" + position); 
 } 
 
 //  Called when a new page is selected  
 @Override 
 public void onPageSelected(int position) { 
  // TODO Auto-generated method stub 
  System.out.println("--onPageSelected--position--:" + position); 
 } 
}