Android图片加载缓存框架Glide

public class MainActivity extends Activity {
  private ImageView glide_iv;
  private ListView glide_lv;
  private static final String URL ="这里写图片url";
  private List<String> urls = new ArrayList<String>();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initDatas();
    glide_iv = (ImageView) findViewById(R.id.glide_iv);
    // 通过下面这句代码把网络图片加载到ImageView中，非常方便
    //Glide的with方法不仅接受Context，还接受Activity 和 Fragment等，Context会自动的从他们获取，使用很方便
    Glide.with(this).load(URL).into(glide_iv);
    glide_lv = (ListView) findViewById(R.id.glide_lv);
    glide_lv.setAdapter(new BaseAdapter() {

      @Override
      public View getView(int arg0, View contentView, ViewGroup arg2) {
        ViewHolder holder=null;
        if (contentView == null) {
          holder=new ViewHolder();
          contentView= LayoutInflater.from(
              MainActivity.this).inflate(R.layout.my_image_view,
              null);
          holder.itemIv = contentView.findViewById(R.id.item_iv);
          contentView.setTag(holder);
        } else {
          holder=(ViewHolder) contentView.getTag();
        }

        String url = urls.get(arg0);
        //在ListView中加载列表图片
        Glide.with(MainActivity.this).load(url).centerCrop()
            .placeholder(R.drawable.ic_launcher).crossFade()
            .into(holder.itemIv);

        return contentView;
      }

      @Override
      public long getItemId(int arg0) {
        // TODO Auto-generated method stub
        return arg0;
      }

      @Override
      public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return urls.get(arg0);
      }

      @Override
      public int getCount() {
        // TODO Auto-generated method stub
        return urls.size();
      }
      class ViewHolder{
        ImageView itemIv;
      }
    });
  }

  /**
   * 添加数据
   */
  private void initDatas() {
    for (int i = 0; i < 5; i++) {
      urls.add(URL);
    }
  }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:padding="20dp" >

  <ImageView
    android:id="@+id/glide_iv"
    android:layout_width="80dp"
    android:layout_height="80dp" />

  <ListView
    android:id="@+id/glide_lv"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:layout_below="@id/glide_iv">
  </ListView>

</RelativeLayout>

<uses-permission android:name="android.permission.INTERNET" >