Android 使用ViewPager实现轮播图效果

写这篇文章只是对今天所学的知识进行加深印象，对ViewPager的一些处理，比如适配器和各个方法的作用等。

先看效果图

这里我是在xml中写的圆点

Drawable文件夹下的xml代码：

Shape_yes.xml:

Shape_no.xml:

选择器

Activity_main.xml:

写一个类ViewPagerAdapter_Circleextends PagerAdapter

public class ViewPagerAdapter_Circle extends PagerAdapter { 
  ArrayList arrayList; 
  Context context; 
  public ViewPagerAdapter_Circle(ArrayList arrayList, Context context) { 
    this.arrayList = arrayList; 
    this.context = context; 
  } 
   
  @Override 
  public int getCount() { 
    return arrayList.size(); 
  } 
   
  @Override 
  public boolean isViewFromObject(View view, Object object) { 
    return view == object;//判断当前要显示的页面 
  } 
   
  @Override 
  public Object instantiateItem(ViewGroup container, int position) { 
    container.addView(arrayList.get(position));//页面添加到container，添加位置 
    return arrayList.get(position); 
  } 
   
  @Override 
  public void destroyItem(ViewGroup container, int position, Object object) { 
    container.removeView(arrayList.get(position)); 
  } 
} 

MainActivity中代码（含注解）

public class MainActivity extends AppCompatActivity { 
  ViewPager viewPager; 
  int imageResIds[]; 
  ArrayList imageViewList;//存图片的集合 
  ArrayList imageViews;//存白点的集合 
  ImageView iv_one,iv_two,iv_three; 
  int oldPostion;//记录原来的位置 
  private Boolean flag; 
  int count=0; 
  Handler handler = new Handler() { 
    @Override 
    public void handleMessage(Message msg) { 
      super.handleMessage(msg); 
      if (msg.what == 0) { 
 viewPager.setCurrentItem(count); 
      } 
    } 
  }; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    //初始化布局 
    initView(); 
    //初始化数据 
    initData(); 
    //设置适配器 
    initAdapter(); 
    //设置圆点 
    initPoint(); 
    flag = true; 
//循环设置播放 
    new Thread() { 
      @Override 
      public void run() { 
 while (flag) { 
   try { 
     Thread.sleep(3000); 
     count++; 
     if (count == 3) { 
count = 0; 
     } 
   } catch (InterruptedException e) { 
     e.printStackTrace(); 
   } 
    
   Message msg = new Message(); 
   msg.what = 0; 
   msg.obj = count; 
   handler.sendMessage(msg); 
 } 
      } 
    }.start(); 
  } 
  private void initView() { 
    viewPager = (ViewPager) findViewById(R.id.vp); 
  } 
  //初始化要显示的数据 
  private void initData() { 
    //图片资源数组 
    imageResIds = new int[]{R.mipmap.a, R.mipmap.b, R.mipmap.c}; 
    imageViewList = new ArrayList<>();//存图片的集合 
    ImageView imageView; 
    for (int i = 0; i < imageResIds.length; i++) { 
      imageView = new ImageView(this); 
      imageView.setBackgroundResource(imageResIds[i]); 
      imageViewList.add(imageView); 
    } 
  } 
  //设置适配器 
  private void initAdapter() { 
    ViewPagerAdapter_Circle myViewPagerAdapter = new ViewPagerAdapter_Circle(imageViewList, this); 
    viewPager.setAdapter(myViewPagerAdapter); 
  } 
   
  private void initPoint() { 
    iv_one = (ImageView) findViewById(R.id.iv_one); 
    iv_two = (ImageView) findViewById(R.id.iv_two); 
    iv_three = (ImageView) findViewById(R.id.iv_three); 
    imageViews = new ArrayList<>(); 
    imageViews.add(iv_one); 
    imageViews.add(iv_two); 
    imageViews.add(iv_three); 
    iv_one.setSelected(true);//设置第一个圆点为true 
     
    viewPager.addonPageChangeListener(new ViewPager.onPageChangeListener() { 
       
      @Override 
      public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { 
      } 
       
      @Override 
      public void onPageSelected(int position) { 
 imageViews.get(position).setSelected(true);//滑动后颜色改变 
 imageViews.get(oldPostion).setSelected(false);//变为初始颜色 
 oldPostion = position;//把滑动后的圆点的position给原来的oldPostion 
      } 
  
      @Override 
      public void onPageScrollStateChanged(int state) { 
      } 
    }); 
  } 
} 

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