android-google Volley framwork(2)

> how to use the common request types that Volley supports:

StringRequest

. Specify a URL and receive a raw string in response. See Setting
Up a Request Queue for an example.

ImageRequest

. Specify a URL and receive an image in response.

JsonObjectRequest

and

JsonArrayRequest

(both subclasses of

JsonRequest

). Specify a URL and get a JSON object or array (respectively) in response.

Here is a sample implementation for an in-memory

LruBitmapCache

class. It extends the

LruCache

class
and implements the

ImageLoader.ImageCache

interface:

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
import android.util.DisplayMetrics;
import com.android.volley.toolbox.ImageLoader.ImageCache;

public class LruBitmapCache extends LruCache<String, Bitmap>
implements ImageCache {

public LruBitmapCache(int maxSize) {
super(maxSize);
}

public LruBitmapCache(Context ctx) {
this(getCacheSize(ctx));
}

@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}

@Override
public Bitmap getBitmap(String url) {
return get(url);
}

@Override
public void putBitmap(String url, Bitmap bitmap) {
put(url, bitmap);
}

// Returns a cache size equal to approximately three screens worth of images.
public static int getCacheSize(Context ctx) {
final DisplayMetrics displayMetrics = ctx.getResources().
getDisplayMetrics();
final int screenWidth = displayMetrics.widthPixels;
final int screenHeight = displayMetrics.heightPixels;
// 4 bytes per pixel
final int screenBytes = screenWidth * screenHeight * 4;

return screenBytes * 3;
}
}

Here is an example of how to instantiate an

ImageLoader

to use this cache:

RequestQueue mRequestQueue; // assume this exists.
ImageLoader mImageLoader = new ImageLoader(mRequestQueue, new LruBitmapCache(
LruBitmapCache.getCacheSize()));

使用Gson解析Json数据。