Volley——（五）ExecutorDelivery

　　在的StringRequest中，咱們這樣一個方法，尚未追蹤過。

    @Override
    protected void deliverResponse(String response) {
        mListener.onResponse(response);
    }

 

　　這個方法，會在咱們請求結束後調用，但它是如何工做的，咱們尚未閱讀。經過對前面代碼的閱讀，咱們會在ExecutorDelivery的run方法中，找到這個方法。　　

 

　　這整個過程要從RequestQueue的初始化提及：

    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在初始時，mDelivery保存了ExecutorDelivery對象的引用。並在start方法中，將其傳給了，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();
        }
    }

 

　　而後在NetworkDispatcher的run方法的最後：

                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，分發請求的響應或是用postError分發錯誤信息。

 

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

　　咱們來看一看ExecutorDelivery具體的代碼：

　　先看構造方法：

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);
            }
        };
    }

 

　　構造方法中，構建了一個執行器。負責將任務分發出去。　　

    @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));
    }

　　這裏的實現比較簡單，只須要看一下ResponseDeliveryRunnable的實現。

    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();
            }
       }
    }

　　咱們能夠看到，這一段實現中，調用deliverResponse，直接將Response中的result成員傳入。

 　　從這裏，咱們能夠看出，StringRequset.java中的:

    @Override
    protected void deliverResponse(String response) {
        mListener.onResponse(response);
    }

　　這裏的response就是Response中的result。

 

Done