google android volley framwork

>volley的特性：

JSON，图像等的异步下载；
网络请求的排序（scheduling）
网络请求的优先级处理
缓存
多级别取消请求
和Activity和生命周期的联动（Activity结束时同时取消所有网络请求）

官方网址：https://android.googlesource.com/platform/frameworks/volley

> Volley is an HTTP library that makes networking for Android apps easier and most importantly, faster. Volley is available through the open AOSP repository.

Volley offers the following benefits:

Automatic scheduling of network requests.
Multiple concurrent network connections.
Transparent disk and memory response caching with standard HTTP cache coherence.
Support for request prioritization.
Cancellation request API. You can cancel a single request, or you can set blocks or scopes of requests to cancel.
Ease of customization, for example, for retry and backoff.
Strong ordering that makes it easy to correctly populate your UI with data fetched asynchronously from the network.
Debugging and tracing tools.

>Volley is not suitable for large download or streaming operations, since Volley holds all responses in memory during parsing. For large download operations, consider using an alternative
like

DownloadManager

.

Volley provides a convenience method

Volley.newRequestQueue

that sets up a

RequestQueue

for you, using default values, and starts the queue. For example:

final TextView mTextView = (TextView) findViewById(R.id.text);
...

// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(this);
String url ="http://www.google.com";

// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Display the first 500 characters of the response string.
mTextView.setText("Response is: "+ response.substring(0,500));
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
mTextView.setText("That didn't work!");
}
});
// Add the request to the RequestQueue.
queue.add(stringRequest);

> In your activity's [code]onStop()

method, cancel all requests that have this tag.[/code]

@Override
protected void onStop () {
super.onStop();
if (mRequestQueue != null) {
mRequestQueue.cancelAll(TAG);
}
}

Take care when canceling requests. If you are depending on your response handler to advance a state or kick off another process, you need to account for this. Again, the response handler will not be called.
> This snippet shows you the steps involved in setting up a

RequestQueue

:

RequestQueue mRequestQueue;

// Instantiate the cache
Cache cache = new DiskBasedCache(getCacheDir(), 1024 * 1024); // 1MB cap

// Set up the network to use HttpURLConnection as the HTTP client.
Network network = new BasicNetwork(new HurlStack());

// Instantiate the RequestQueue with the cache and network.
mRequestQueue = new RequestQueue(cache, network);

// Start the queue
mRequestQueue.start();

String url ="http://www.example.com";

// Formulate the request and handle the response.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Do something with the response
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Handle error
}
});

// Add the request to the RequestQueue.
mRequestQueue.add(stringRequest);

> Here is an example of a singleton class that provides

RequestQueue

and

ImageLoader

functionality:

public class MySingleton {
private static MySingleton mInstance;
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
private static Context mCtx;

private MySingleton(Context context) {
mCtx = context;
mRequestQueue = getRequestQueue();

mImageLoader = new ImageLoader(mRequestQueue,
new ImageLoader.ImageCache() {
private final LruCache<String, Bitmap>
cache = new LruCache<String, Bitmap>(20);

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

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

public static synchronized MySingleton getInstance(Context context) {
if (mInstance == null) {
mInstance = new MySingleton(context);
}
return mInstance;
}

public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
// getApplicationContext() is key, it keeps you from leaking the
// Activity or BroadcastReceiver if someone passes one in.
mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
}
return mRequestQueue;
}

public <T> void addToRequestQueue(Request<T> req) {
getRequestQueue().add(req);
}

public ImageLoader getImageLoader() {
return mImageLoader;
}
}

Here are some examples of performing

RequestQueue

operations using the singleton class:

// Get a RequestQueue
RequestQueue queue = MySingleton.getInstance(this.getApplicationContext()).
getRequestQueue();

// ...

// Add a request (in this example, called stringRequest) to your RequestQueue.
MySingleton.getInstance(this).addToRequestQueue(stringRequest);

<未完待续>