Volley提供2个静态方法：
public static RequestQueue newRequestQueue(Context context) ｛｝ public static RequestQueue newRequestQueue(Context context, HttpStack stack) ｛｝
第一个直接调用第二个的newRequestQueue(context, null);方法，返回都是一个RequestQueue 对象
以ImageLoader为例 构造方法
public ImageLoader(RequestQueue queue, ImageCache imageCache) {
mRequestQueue = queue;
mCache = imageCache;
}
需要一个RequestQueue 对象 和一个ImageCache对象 ，RequestQueue 可以通过Volley类中的静态方法newRequestQueue(Context context) 获得，而ImageCache 则是一个interface
public interface ImageCache {
public Bitmap getBitmap(String url);
public void putBitmap(String url, Bitmap bitmap);
}
实现此接口,即上一文章中Cache包下的BitmapCache，赋值给mCache对象
mCache中缓存key value，key规则为String key = "#W"+maxWidth+"#H"+ maxHeight +url;
再来看下面方法
参数：defaultImageResId:未开始下载显示的图片Id,如果传递0则不显示任何东西
errorImageResId:下载显示的图片Id,如果传递0则不显示任何东西
返回值：ImageListener
public static ImageListener getImageListener(final ImageView view,
final int defaultImageResId, final int errorImageResId) {
...
...//直接new一个ImageListener
@Override public void onResponse(ImageContainer response, boolean isImmediate)
{ if (response.getBitmap() != null)
{ //response有值设置ImageView显示图片
view.setImageBitmap(response.getBitmap()); } else if (defaultImageResId != ) { view.setImageResource(defaultImageResId); } } }
response.getBitmap()中的bitmap是通过BatchedImageRequest中的batchResponse（），
通过一个ImageContainer类中的Interface:ImageListerner.onResponse回调回来的
private void batchResponse(String cacheKey, BatchedImageRequest request,
final VolleyError error) {
mBatchedResponses.put(cacheKey, request);
// If we don't already have a batch delivery runnable in flight, make a new one.
// Note that this will be used to deliver responses to all callers in mBatchedResponses.
if (mRunnable == null) {
mRunnable = new Runnable() {
@Override
public void run() {
for (BatchedImageRequest bir : mBatchedResponses.values()) {
for (ImageContainer container : bir.mContainers) {
if (container.mListener == null) {
continue;
}
if (error == null) {
//取得数据
container.mBitmap = bir.mResponseBitmap;
//通过ImageContainer中的mListener，即ImageListener中的onResponse（）方法回调
container.mListener.onResponse(container, false);
} else {
container.mListener.onErrorResponse(error);
}
}
}
mBatchedResponses.clear();
mRunnable = null;
} };
// Post the runnable.
mHandler.postDelayed(mRunnable, mBatchResponseDelayMs);
}
}