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在的StringRequest中，我们这样一个方法，还没有追踪过。
@Override protected void deliverResponse(String response) { mListener.onResponse(response); }
这个方法，会在我们请求结束后调用，但它是如何工作的，我们还没有阅读。通过对前面代码的阅读，我们会在ExecutorDelivery的run方法中，找到这个方法。
这整个过程要从RequestQueue的初始化说起：
public RequestQueue(Cache cache, Network network, int threadPoolSize) { this(cache, network, threadPoolSize, new ExecutorDelivery(new Handler(Looper.getMainLooper()))); } public RequestQueue(Cache cache, Network network, int threadPoolSize, ResponseDelivery delivery) { mCache = cache; mNetwork = network; mDispatchers = new NetworkDispatcher[threadPoolSize]; mDelivery = delivery; }
RequestQueue在初始时，mDelivery保存了ExecutorDelivery对象的引用。并在start方法中，将其传给了，NetworkDispatcher和CacheDispatcher:
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(); } }
然后在NetworkDispatcher的run方法的最后：
mDelivery.postResponse(request, response); } catch (VolleyError volleyError) { volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs); parseAndDeliverNetworkError(request, volleyError); } catch (Exception e) { VolleyLog.e(e, "Unhandled exception %s", e.toString()); VolleyError volleyError = new VolleyError(e); volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs); mDelivery.postError(request, volleyError); }
用postResponse方法，分发请求的响应或是用postError分发错误信息。
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我们来看一看ExecutorDelivery具体的代码：
先看构造方法：
public class ExecutorDelivery implements ResponseDelivery { /** Used for posting responses, typically to the main thread. */ private final Executor mResponsePoster; /** * Creates a new response delivery interface. * @param handler {@link Handler} to post responses on */ public ExecutorDelivery(final Handler handler) { // Make an Executor that just wraps the handler. mResponsePoster = new Executor() { @Override public void execute(Runnable command) { handler.post(command); } }; }
构造方法中，构建了一个执行器。负责将任务分发出去。
@Override public void postResponse(Request<?> request, Response<?> response) { postResponse(request, response, null); } @Override public void postResponse(Request<?> request, Response<?> response, Runnable runnable) { request.markDelivered(); request.addMarker("post-response"); mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable)); } @Override public void postError(Request<?> request, VolleyError error) { request.addMarker("post-error"); Response<?> response = Response.error(error); mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, null)); }
这里的实现比较简单，只需要看一下ResponseDeliveryRunnable的实现。
private class ResponseDeliveryRunnable implements Runnable { private final Request mRequest; private final Response mResponse; private final Runnable mRunnable; public ResponseDeliveryRunnable(Request request, Response response, Runnable runnable) { mRequest = request; mResponse = response; mRunnable = runnable; } @SuppressWarnings("unchecked") @Override public void run() { // If this request has canceled, finish it and don‘t deliver. if (mRequest.isCanceled()) { mRequest.finish("canceled-at-delivery"); return; } // Deliver a normal response or error, depending. if (mResponse.isSuccess()) { mRequest.deliverResponse(mResponse.result); } else { mRequest.deliverError(mResponse.error); } // If this is an intermediate response, add a marker, otherwise we‘re done // and the request can be finished. if (mResponse.intermediate) { mRequest.addMarker("intermediate-response"); } else { mRequest.finish("done"); } // If we have been provided a post-delivery runnable, run it. if (mRunnable != null) { mRunnable.run(); } } }
我们可以看到，这一段实现中，调用deliverResponse，直接将Response中的result成员传入。
从这里，我们可以看出，StringRequset.java中的:
@Override protected void deliverResponse(String response) { mListener.onResponse(response); }
这里的response就是Response中的result。
Done
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原文地址：http://www.cnblogs.com/fishbone-lsy/p/5531557.html
