结合开发文档分析volley(二)

来源：互联网发布：淘宝代码装修教程编辑：程序博客网时间：2024/05/19 13:07

这篇笔记记录Setting Up a RequestQueue。设置一个RequestQueue.
创建一个RequestQueue，需要两个东西—-NetWork和Cache。Network做网络有关工作，Cache做缓冲工作。
在Volley有NetWork和Cache的实现——-DiskBasedCache和BasicNetwork。DiskBasedCache保证了一个response对应一个文件，BasicNetwork提供了基于AndroidHttpClient or HttpURLConnection的网络传输。关于BasicNetwork什么时候基于AndroidHttpClient ，什么时候基于HttpURLConnection，下面的代码解释了。

HttpStack stack;...// If the device is running a version >= Gingerbread...if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) {    // ...use HttpURLConnection for stack.} else {    // ...use AndroidHttpClient for stack.}Network network = new BasicNetwork(stack);

android2.3以上（包括2.3）基于HttpURLConnection。

接下来，创建RequestQueue。

RequestQueue mRequestQueue;// Instantiate the cacheCache 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 queuemRequestQueue.start();

上一篇笔记记录了用 Volley.newRequestQueue创建了一个RequestQueue。看源码。

public static RequestQueue newRequestQueue(Context context, HttpStack stack, int maxDiskCacheBytes) {        File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);        String userAgent = "volley/0";        try {            String packageName = context.getPackageName();            PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);            userAgent = packageName + "/" + info.versionCode;        } catch (NameNotFoundException e) {        }        if (stack == null) {            if (Build.VERSION.SDK_INT >= 9) {                stack = new HurlStack();            } else {                // Prior to Gingerbread, HttpUrlConnection was unreliable.                // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html                stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));            }        }        Network network = new BasicNetwork(stack);        RequestQueue queue;        if (maxDiskCacheBytes <= -1)        {            // No maximum size specified            queue = new RequestQueue(new DiskBasedCache(cacheDir), network);        }        else        {            // Disk cache size specified            queue = new RequestQueue(new DiskBasedCache(cacheDir, maxDiskCacheBytes), network);        }        queue.start();        return queue;    }

可以看到这方法也是用了NetWork和Cache创建了RequestQueue,然后queue.start(); start()的工作是什么？

public void start() {        stop();  // Make sure any currently running dispatchers are stopped.        // Create the cache dispatcher and start it.        mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);        mCacheDispatcher.start();        // Create network dispatchers (and corresponding threads) up to the pool size.        for (int i = 0; i < mDispatchers.length; i++) {            NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,                    mCache, mDelivery);            mDispatchers[i] = networkDispatcher;            networkDispatcher.start();        }    }

看了代码会知道，start是将上一篇笔记提到的CacheDispatcher线程和NetworkDispatcher线程开启。

RequestQueue的单例模式
单例模式是为了使RequestQueue的生命周期和app的一样。

    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;    }}

0 0