Android UI开发第三十六篇——使用Volley加载图片列表
Android开发者可能会使用Universal Image Loader或者Square`s newer Picasso这些第三方的库去处理图片的加载，那么Volley是怎么加载图片列表的呢，这一篇文章会介绍使用Volley加载图片列表。
在Google I/O介绍Volley的时候，Ficus Kirpatrick讲了很多关于Volley如何的有助于图片加载。但是，你会发现在Volley作为图片加载解决方案的时候，Volley虽然自己处理了L2的缓存，可是它没有处理L1的缓存。它给出了ImageCache接口类，让开发者自己根据自己的需求实现自己L1缓存，这样你可以实现LRU、FIFO等算法的缓存。
Volley加载图片时需要使用ImageLoader，ImageLoader初始化一次。展示图片的View可以使用ImageView或者Volley自定义的NetworkImageView。NetworkImageView可以使用setUrl方法获取图片。下面为两种View加载图片的方式。
使用ImageView：
public class VolleyImageViewListAdapter extends BaseAdapter{
private static final String TAG = "VolleyListAdapter";
private Context mContext;
private String[] urlArrays;
private ImageLoader mImageLoader;
public VolleyImageViewListAdapter(Context context, String []url) {
this.mContext = context;
urlArrays = url;
RequestQueue mQueue = Volley.newRequestQueue(context);
mImageLoader = new ImageLoader(mQueue, new BitmapCache());
}
@Override
public int getCount() {
return urlArrays.length;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder = null;
if (convertView == null) {
convertView = LayoutInflater.from(mContext).inflate(
R.layout.volley_image_list_item, null);
viewHolder = new ViewHolder();
viewHolder.mTextView = (TextView) convertView
.findViewById(R.id.tv_tips);
viewHolder.mImageView = (ImageView) convertView
.findViewById(R.id.iv_image);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
String url = "";
url = urlArrays[position % urlArrays.length];
viewHolder.mTextView.setText(position+"|"+urlArrays.length) ;
ImageListener listener = ImageLoader.getImageListener(viewHolder.mImageView, android.R.drawable.ic_menu_rotate, android.R.drawable.ic_delete);
mImageLoader.get(url, listener);
return convertView;
}
static class ViewHolder {
TextView mTextView;
ImageView mImageView;
}
public class BitmapCache implements ImageCache {
private LruCache<String, Bitmap> mCache;
public BitmapCache() {
int maxSize = 10 * 1024 * 1024;
mCache = new LruCache<String, Bitmap>(maxSize) {
@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
};
}
@Override
public Bitmap getBitmap(String url) {
return mCache.get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
mCache.put(url, bitmap);
}
}
}
使用NetworkImageView：
public class VolleyListAdapter extends BaseAdapter{
private static final String TAG = "VolleyListAdapter";
private Context mContext;
private String[] urlArrays;
public VolleyListAdapter(Context context, String []url) {
this.mContext = context;
urlArrays = url;
}
@Override
public int getCount() {
return urlArrays.length;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder = null;
if (convertView == null) {
convertView = LayoutInflater.from(mContext).inflate(
R.layout.volley_list_item, null);
viewHolder = new ViewHolder();
viewHolder.mTextView = (TextView) convertView
.findViewById(R.id.tv_tips);
viewHolder.mImageView = (NetworkImageView) convertView
.findViewById(R.id.iv_image);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
String url = "";
url = urlArrays[position % urlArrays.length];
viewHolder.mTextView.setText(position+"|"+urlArrays.length) ;
viewHolder.mImageView.setImageUrl(url, ImageCacheManager.getInstance().getImageLoader());
return convertView;
}
static class ViewHolder {
TextView mTextView;
NetworkImageView mImageView;
}
}
效果图：
/**
* @author 张兴业