編輯:關於Android編程
做安卓一年有余,意識到網絡請求框架算是很重要的一塊,考慮到Volley是谷歌自帶的,決定好好研究研究源碼,去理理邏輯思路
首先呢,Volley去哪裡獲取,看下圖即可,在安卓源碼的frameworks目錄下,然後導入到eclipse中即可去研究了
使用Volley的第一步,首先要調用Volley.newRequestQueue(context)方法來獲取一個RequestQueue對象,那麼我們自然要從這個方法開始看起了,代碼如下所示
public static RequestQueue newRequestQueue(Context context, HttpStack stack) { 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 = new RequestQueue(new DiskBasedCache(cacheDir), network); queue.start(); return queue; }
以上代碼中做了如下幾件事:
1、創建緩存目錄
File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
getCacheDir()方法用於獲取/data/data//cache目錄,創建volley的目錄,用來做後續的緩存目錄
2、創建對應對應版本的HttpStack實例
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)); }上面這段代碼是Build.VERSION.SDK_INT是獲取當前手機版本,則創建一個HurlStack的實例,否則就創建一個HttpClientStack的實例。實際上HurlStack的內部就是使用HttpURLConnection進行網絡通訊的,而HttpClientStack的內部則是使用HttpClient進行網絡通訊的
public BasicNetwork(HttpStack httpStack) { this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE)); } public BasicNetwork(HttpStack httpStack, ByteArrayPool pool) { mHttpStack = httpStack; mPool = pool; }構造函數著重看new ByteArrayPool(DEFAULT_POOL_SIZE),那麼ByteArrayPool這個類做了什麼操作?
在對響應的實體進行操作的時候,使用到了byte[] ,由於volley是輕量級頻次高的網絡請求框架,因此會大量使用到byte[] ,這樣的話會頻繁創建和銷毀byte[]。為了提高性能,volley定義了一個byte[]緩沖池,即ByteArrayPool 。
在ByteArrayPool 內,定義了 兩個集合,
private ListmBuffersByLastUse = new LinkedList (); private List mBuffersBySize = new ArrayList (64);
分別是存儲按按使用先後順序排列byte[]的list和大小順序排列byte[]的list 。在volley中所需要使用到的byte[]從該緩沖池中來取,當byte[]使用完畢後再歸還到該緩沖池,從而避免頻繁的創建和銷毀byte[]。
看下ByteArrayPool的如下方法:getBuf:從池中獲取一個可用的byte[],如果沒有,就創建一個。參數為想要獲取多大長度的byte[]
returnBuf:當使用完一個byte[]後,將該byte[]返回到池中
trim:當現有字節總數超過了設定的界限,那麼需要清理
4、創建RequestQueue對象,在RequestQueue構造方法中,進行如下初始化操作
public RequestQueue(Cache cache, Network network, int threadPoolSize, ResponseDelivery delivery) { mCache = cache; mNetwork = network; mDispatchers = new NetworkDispatcher[threadPoolSize]; mDelivery = delivery; }我們看看初始化操作都做了什麼?
Cache cache =new DiskBasedCache(cacheDir)這個是網絡數據的磁盤緩存
Network network = new BasicNetwork(stack);就是Network類
NetworkDispatcher[] mDispatchers=new NetworkDispatcher[threadPoolSize];就是請求數據的網絡線程
ResponseDelivery mDelivery=new ExecutorDelivery(new Handler(Looper.getMainLooper())volley中默認的響應傳遞類
5、看下queue.start();這個方法,也就是最後一步啟動線程進行數據訪問,我們在RequestQueue看看start做了什麼呢?
Volley最主要的功能其實就是跟網絡打交道,然後從網絡中獲取相對應的數據,如果只有網絡請求線程NetworkDispatcher,沒有緩存線程(CacheDispatcher),顯然不是很理想,所以在queue.start();方法中可以看到
public void start() { stop(); mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery); mCacheDispatcher.start(); for (int i = 0; i < mDispatchers.length; i++) { NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork, mCache, mDelivery); mDispatchers[i] = networkDispatcher; networkDispatcher.start(); } }
mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery); mCacheDispatcher.start();生成了緩存線程CacheDispatcher,緩存中沒有對應的記錄的話,還是會將其扔到網絡隊列中,由網絡線程(NetworkDispatcher)來干活
到此位置,我們就知道了構造方法中有磁盤緩存DiskBasedCache、Network類、網絡主請求線程mDispatchers、請求結果的相應類ResponseDelivery、以及queue.start()中的網絡緩存線程CacheDispatcher
我們之前寫Volley的例子都是這樣操作的:mQueue.add(stringRequest); 之類的操作
publicRequest add(Request request) { // Tag the request as belonging to this queue and add it to the set of current requests. request.setRequestQueue(this); synchronized (mCurrentRequests) { mCurrentRequests.add(request); } // Process requests in the order they are added. request.setSequence(getSequenceNumber()); request.addMarker("add-to-queue"); // If the request is uncacheable, skip the cache queue and go straight to the network. if (!request.shouldCache()) { mNetworkQueue.add(request); return request; } // Insert request into stage if there's already a request with the same cache key in flight. synchronized (mWaitingRequests) { String cacheKey = request.getCacheKey(); if (mWaitingRequests.containsKey(cacheKey)) { // There is already a request in flight. Queue up. Queue > stagedRequests = mWaitingRequests.get(cacheKey); if (stagedRequests == null) { stagedRequests = new LinkedList >(); } stagedRequests.add(request); mWaitingRequests.put(cacheKey, stagedRequests); if (VolleyLog.DEBUG) { VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", cacheKey); } } else { // Insert 'null' queue for this cacheKey, indicating there is now a request in // flight. mWaitingRequests.put(cacheKey, null); mCacheQueue.add(request); } return request; } }
可以看到,在!request.shouldCache()來判斷要不要去緩存中查詢,如果是去緩存中查詢,那麼就會把請求放到CacheQueue中,如果沒有設置緩存則在mNetworkQueue.add(request);直接將這條請求加入網絡請求隊列。在默認情況下,每條請求都是可以緩存的,當然我們也可以調用Request的setShouldCache(false)方法來改變這一默認行為。
那麼既然默認每條請求都是可以緩存的,自然就被添加到了緩存隊列中,於是一直在後台等待的緩存線程就要開始運行起來了,
會去調用queue.start();那麼就看看start方法中都干什麼吧,如下:
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(); for (int i = 0; i < mDispatchers.length; i++) { NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork, mCache, mDelivery); mDispatchers[i] = networkDispatcher; networkDispatcher.start(); } }private static final int DEFAULT_NETWORK_THREAD_POOL_SIZE = 4;
而默認情況下for循環會執行四次,也就是說當調用了Volley.newRequestQueue(context)之後,就會有五個線程一直在後台運行,不斷等待網絡請求的到來,其中1個CacheDispatcher是緩存線程,4個NetworkDispatcher是網絡請求線程。
既然有5個線程運行,我們就先看看CacheDispatcher緩存線程做了什麼操作?
public void run() { if (DEBUG) VolleyLog.v("start new dispatcher"); Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); // 初始化緩存 mCache.initialize(); while (true) { try { // 從緩存隊列中獲取一個請求 final Request request = mCacheQueue.take(); request.addMarker("cache-queue-take"); // 如果請求已經被取消,則重新獲取請求 if (request.isCanceled()) { request.finish("cache-discard-canceled"); continue; } // 根據request的cacheKey從緩存中得到對應的記錄 Cache.Entry entry = mCache.get(request.getCacheKey()); if (entry == null) { request.addMarker("cache-miss"); // 這裡說明緩存中沒有對應的記錄,那麼需要去網絡中獲取,那麼就將它放到Network的隊列中 mNetworkQueue.put(request); continue; } // 如果緩存中有記錄,但是已經過期了或者失效了,也需要去網絡獲取,放到Network隊列中 if (entry.isExpired()) { request.addMarker("cache-hit-expired"); request.setCacheEntry(entry); mNetworkQueue.put(request); continue; } // 如果上面的情況都不存在,說明緩存中存在這樣記錄,那麼就調用request的parseNetworkResponse方法,獲取一個響應Response request.addMarker("cache-hit"); Response response = request .parseNetworkResponse(new NetworkResponse(entry.data, entry.responseHeaders)); request.addMarker("cache-hit-parsed"); if (!entry.refreshNeeded()) { // 緩存記錄,不需要更新,那麼就直接調用mDelivery,傳回給主線程去更新。 mDelivery.postResponse(request, response); } else { // 還存在這樣一種情況,緩存記錄存在,但是它約定的生存時間已經到了(還未完全過期,叫軟過期),可以將其發送到主線程去更新 // 但同時,也要從網絡中更新它的數據 request.addMarker("cache-hit-refresh-needed"); request.setCacheEntry(entry); // Mark the response as intermediate. response.intermediate = true; // 將其傳回主線程的同時,將請求放到Network隊列中。 mDelivery.postResponse(request, response, new Runnable() { @Override public void run() { try { mNetworkQueue.put(request); } catch (InterruptedException e) { // Not much we can do about this. } } }); } } catch (InterruptedException e) { // We may have been interrupted because it was time to quit. if (mQuit) { return; } continue; } } }
1)初始化本地緩存
2)開始一個無限的循環,調用 mCacheQueue的take方法,來獲得一個請求,而mCacheQueue是一個BlockingQueue,也就是說,當隊列中沒有請求的時候,take方法就會一直阻塞在這裡,等待隊列中的請求,而一旦隊列中有新的請求進來了,那麼它就會馬上執行下去。
3)判斷請求是否已經取消,如果已經被取消了,則不需要再走下去。4)根據請求的CacheKey去緩存中尋找相對應的記錄,如果找不到對應的記錄,或者對應的記錄過期了,則將其放到NetworkQueue隊列中。
5)緩存中存在相對應的記錄,那麼調用每個請求具體的實現方法 parseNetworkResponse函數,根據具體的請求去解析得到對應的響應Response對象。
6)獲得Response對象之後,還會再進行判斷這個請求是不是進行一次網絡的更新,這是根據記錄的soft-ttl (time-to-live)屬性從這裡也可以看到,expired的判斷跟refreshNeed的判斷是兩個字段,一個是ttl,一個是softTtl。
如果需要進行更新,那麼就會在發送響應結果回主線程更新的同時,再將請求放到NetworkQueue中,從網絡中更新請求對應的數據。如果不需要,則直接將結果調用mDelivery傳回主線程進行UI的更新。
Volley最主要的功能其實就是跟網絡打交道,然後從網絡中獲取相對應的數據,雖然有緩存線程(CacheDispatcher),但是如果緩存中沒有對應的記錄的話,還是會將其扔到網絡隊列中,由網絡線程(NetworkDispatcher)來干活。
networkDispatcher.start();我們看看網絡線程這裡面做了什麼操作?
@Override public void run() { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); Request request; while (true) { try { // 從隊列中獲取一個請求,如果沒有請求,則會一直阻塞 request = mQueue.take(); } catch (InterruptedException e) { // We may have been interrupted because it was time to quit. if (mQuit) { return; } continue; } try { request.addMarker("network-queue-take"); // 判斷請求有沒有取消,如果取消,則不必再繼續 if (request.isCanceled()) { request.finish("network-discard-cancelled"); continue; } addTrafficStatsTag(request); // 調用mNetwork去跟網絡打交道 NetworkResponse networkResponse = mNetwork.performRequest(request); request.addMarker("network-http-complete"); // 如果服務器返回一個未修改(304)的響應,並且這個請求已經發送過響應對象,不需要再繼續,因為沒改過 if (networkResponse.notModified && request.hasHadResponseDelivered()) { request.finish("not-modified"); continue; } // 分析響應的數據,返回Response對象 Response response = request.parseNetworkResponse(networkResponse); request.addMarker("network-parse-complete"); // 根據request的shouldCache字段來判斷是不是需要緩存,如果需要,則將其放到mCache中。 if (request.shouldCache() && response.cacheEntry != null) { mCache.put(request.getCacheKey(), response.cacheEntry); request.addMarker("network-cache-written"); } // 調用 mDelivery將Response對象傳回主線程進行UI的更新。 request.markDelivered(); mDelivery.postResponse(request, response); } catch (VolleyError volleyError) { //有錯誤,也會調用到mDelivery,將錯誤信息傳回到主線程,進行提示 parseAndDeliverNetworkError(request, volleyError); } catch (Exception e) { VolleyLog.e(e, "Unhandled exception %s", e.toString()); mDelivery.postError(request, new VolleyError(e)); } } }
網絡線程(NetworkDispatcher)主要做了幾件事情:
1)調用 mQueue的take()方法從隊列中獲取請求,如果沒有請求,則一直阻塞在那裡等待,直到隊列中有新的請求到來。
2)判斷請求有沒有被取消,如果被取消,則重新獲取請求。
3)調用Network對象將請求發送到網絡中,並返回一個 NetworkResponse對象。
4)調用請求的pareseNetworkResonse方法,將NetworkResponse對象解析成相對應的Response對象。
5)判斷請求是否需要緩存,如果需要緩存,則將其Response中cacheEntry對象放到緩存mCache中。
6)調用 mDelivery將Response對象傳到主線程中進行UI更新。
可以看到,網絡線程其實是調用 Network對象去實現跟網絡進行溝通的,而在Volley中,默認的Network實現類,則是BasicNetwork類。我們去看下mNetwork.performRequest(request);做了什麼操作?
public NetworkResponse performRequest(Request request) throws VolleyError { long requestStart = SystemClock.elapsedRealtime(); while (true) { HttpResponse httpResponse = null; byte[] responseContents = null; MapresponseHeaders = new HashMap (); try { // 添加頭部信息 Map headers = new HashMap (); addCacheHeaders(headers, request.getCacheEntry()); //調用HttpStack對象去網絡中獲取數據,返回一個HttpResponse對象 httpResponse = mHttpStack.performRequest(request, headers); StatusLine statusLine = httpResponse.getStatusLine(); int statusCode = statusLine.getStatusCode(); // 獲取服務器的響應頭 數組,然後轉為Map集合 responseHeaders = convertHeaders(httpResponse.getAllHeaders()); // 從響應的狀態行獲取狀態編碼,如果是304(未修改),說明之前已經取過數據了,那麼就直接利用緩存中的數據,構造一個NetworkResonse對象 if (statusCode == HttpStatus.SC_NOT_MODIFIED) { return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, request.getCacheEntry() == null ? null : request.getCacheEntry().data, responseHeaders, true); } // 有些響應是不帶內容的,比如響應狀態編碼是204的話,添加一個空的byte作為內容,後面好統一處理。 if (httpResponse.getEntity() != null) { responseContents = entityToBytes(httpResponse.getEntity()); } else { // Add 0 byte response as a way of honestly representing a // no-content request. responseContents = new byte[0]; } // if the request is slow, log it. long requestLifetime = SystemClock.elapsedRealtime() - requestStart; logSlowRequests(requestLifetime, request, responseContents, statusLine); if (statusCode < 200 || statusCode > 299) { throw new IOException(); } //構建NetworkResponse對象 return new NetworkResponse(statusCode, responseContents, responseHeaders, false); } catch (SocketTimeoutException e) { attemptRetryOnException("socket", request, new TimeoutError()); } catch (ConnectTimeoutException e) { attemptRetryOnException("connection", request, new TimeoutError()); } catch (MalformedURLException e) { throw new RuntimeException("Bad URL " + request.getUrl(), e); } catch (IOException e) { int statusCode = 0; NetworkResponse networkResponse = null; if (httpResponse != null) { statusCode = httpResponse.getStatusLine().getStatusCode(); } else { throw new NoConnectionError(e); } VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl()); if (responseContents != null) { networkResponse = new NetworkResponse(statusCode, responseContents, responseHeaders, false); if (statusCode == HttpStatus.SC_UNAUTHORIZED || statusCode == HttpStatus.SC_FORBIDDEN) { attemptRetryOnException("auth", request, new AuthFailureError(networkResponse)); } else { // TODO: Only throw ServerError for 5xx status codes. throw new ServerError(networkResponse); } } else { throw new NetworkError(networkResponse); } } } }
BasicNetwork做的事情如下:
1)對於已經有緩存的請求,添加其頭部信息
2)調用 HttpStack 對象去網絡中獲取數據,返回httpResonse 對象。
3)根據狀態編碼來返回不同的Response對象,如304(未修改)就返回緩存中的數據,如果不是,則根據響應中的數據,重新構造一個NetworkResponse對象。
4)BasicNetwork實現了重試的機制,如果第一次從網絡獲取失敗,默認會重新再嘗試一次,如果失敗,則會將Error返回,默認的實現類是DefaultRetryPolicy類。
在上面的代碼中httpResponse = mHttpStack.performRequest(request, headers);是通過HttpStack對象去請求返回HttpResponse對象,然後在獲取HttpResponse對象的一些信息,然後封裝為NetworkResponse返回給NetworkDispatcher,
我們要看下mHttpStack如何處理網絡請求的?
public HttpResponse performRequest(Request request, MapadditionalHeaders) throws IOException, AuthFailureError { String url = request.getUrl(); HashMap map = new HashMap (); map.putAll(request.getHeaders());//默認為null map.putAll(additionalHeaders);//添加頭部,主要是緩存相關的頭部信息 if (mUrlRewriter != null) { String rewritten = mUrlRewriter.rewriteUrl(url); if (rewritten == null) { throw new IOException("URL blocked by rewriter: " + url); } url = rewritten; } URL parsedUrl = new URL(url); HttpURLConnection connection = openConnection(parsedUrl, request);//打開Connection for (String headerName : map.keySet()) { //將Map的對象添加到Connection的屬性中 connection.addRequestProperty(headerName, map.get(headerName)); } //設置connection方法,主要是設置Method屬性和Content(for post/put) setConnectionParametersForRequest(connection, request); //設置Http 協議 ProtocolVersion protocolVersion = new ProtocolVersion("HTTP", 1, 1); int responseCode = connection.getResponseCode(); if (responseCode == -1) { throw new IOException("Could not retrieve response code from HttpUrlConnection."); } StatusLine responseStatus = new BasicStatusLine(protocolVersion, connection.getResponseCode(), connection.getResponseMessage()); BasicHttpResponse response = new BasicHttpResponse(responseStatus); //獲得Response的流,並將其解析成對應的HttpEntity對象,設置給Response.entity字段 response.setEntity(entityFromConnection(connection)); for (Entry > header : connection.getHeaderFields().entrySet()) { if (header.getKey() != null) { Header h = new BasicHeader(header.getKey(), header.getValue().get(0)); response.addHeader(h); } } return response; }
HttpURLConnection是Android3.0以後才提供的一個網絡訪問類,而HurlStack類,也正是H(ttp)URL的縮寫,所以這個類,其實就是基於HttpUrlConnection的實現,其步驟如下:
1)從Request中獲得url參數,根據url參數構造URL對象,而URL對象是java提供的獲取網絡資源的一個封裝好的實用類。 2)從URL對象打開Connection,並設置connection的超時,緩存,讓網絡資源寫入等屬性。
3)調用方法setConnectionParametersForRequest 來設置 Method屬性,如果是Post或者Put的話,還要設置Content內容。
4)設置Http 協議,這裡基本上是1.1了。 5)獲得Response的流,並將其解析成對應的HttpEntity對象,設置給Response.entity字段,返回給BasicNetwork。
BasicHttpResponse response = new BasicHttpResponse(responseStatus); response.setEntity(entityFromConnection(connection));
然後在封裝為HttpResponse對象返回給BasicNetwork對象
在BasicNetwork中在封裝為 return new NetworkResponse(statusCode, responseContents, responseHeaders, false);返回給NetworkDispatcher對象
最後在NetworkDispatcher中,進行 Responseresponse = request.parseNetworkResponse(networkResponse);將請求結果解析成需要的類型,將NetworkResponse解析成Response
下面的代碼拿StringRequest方式說明
protected ResponseparseNetworkResponse(NetworkResponse response) { String parsed; try { parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers)); } catch (UnsupportedEncodingException e) { parsed = new String(response.data); } return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response)); }
public static Cache.Entry parseCacheHeaders(NetworkResponse response) { long now = System.currentTimeMillis(); Map然後NetworkDispatcher拿著解析好的 Responseresponse東東, 去mDelivery.postResponse(request, response);進行ui更新操作headers = response.headers; long serverDate = 0; long serverExpires = 0; long softExpire = 0; long maxAge = 0; boolean hasCacheControl = false; String serverEtag = null; String headerValue; headerValue = headers.get("Date"); if (headerValue != null) { serverDate = parseDateAsEpoch(headerValue); } headerValue = headers.get("Cache-Control"); if (headerValue != null) { hasCacheControl = true; String[] tokens = headerValue.split(","); for (int i = 0; i < tokens.length; i++) { String token = tokens[i].trim(); if (token.equals("no-cache") || token.equals("no-store")) { return null; } else if (token.startsWith("max-age=")) { try { maxAge = Long.parseLong(token.substring(8)); } catch (Exception e) { } } else if (token.equals("must-revalidate") || token.equals("proxy-revalidate")) { maxAge = 0; } } } headerValue = headers.get("Expires"); if (headerValue != null) { serverExpires = parseDateAsEpoch(headerValue); } serverEtag = headers.get("ETag"); // Cache-Control takes precedence over an Expires header, even if both exist and Expires // is more restrictive. if (hasCacheControl) { softExpire = now + maxAge * 1000; } else if (serverDate > 0 && serverExpires >= serverDate) { // Default semantic for Expire header in HTTP specification is softExpire. softExpire = now + (serverExpires - serverDate); } Cache.Entry entry = new Cache.Entry(); entry.data = response.data; entry.etag = serverEtag; entry.softTtl = softExpire; entry.ttl = entry.softTtl; entry.serverDate = serverDate; entry.responseHeaders = headers; return entry; }
回頭看NetworkDispatcher類run方法中的 mDelivery.postResponse(request, response);如何去更新ui界面的?
請求結果的交付是通過ResponseDelivery接口完成的,它有一個實現類ExecutorDelivery, 主要有postResponse()與postError()兩個方法,分別在請求成功或失敗時將結果提交給請求發起者。
看 mDelivery.postResponse(request, response);方法的具體實現。每post一個response,都會調用ResponseDeliveryRunnable的run()方法。在這個run()方法中,會通過mRequest.deliverResponse(mResponse.result)來傳遞response的result,這個result其實就是已經解析好的響應結果,比如一個表示處理結果的字符串或一個User對象
@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)); }
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(); } }
在mRequest.deliverResponse(mResponse.result)方法中,有ImageRequest、JsonRequest、StringRequest請求方式
我們就簡單看StringRequest的實現方法,這裡有一個接口去外部實現
protected void deliverResponse(String response) { mListener.onResponse(response); }是通過構造方式傳入進來接口、默認是get方式
public StringRequest(int method, String url, Listenerlistener, ErrorListener errorListener) { super(method, url, errorListener); mListener = listener; } public StringRequest(String url, Listener listener, ErrorListener errorListener) { this(Method.GET, url, listener, errorListener); }
其實還是用的Handler,Looper,MessageQueue的那套機制。 在Volley初始化一個RequestQueue的時候,會調用RequestQueue的如下構造函數,它構建了一個ExecutorDelivery對象,並把一個與主線程的Looper關聯的一個Handler,大家還記得如下的構造方法沒?
public RequestQueue(Cache cache, Network network, int threadPoolSize) { this(cache, network, threadPoolSize, new ExecutorDelivery(new Handler( Looper.getMainLooper()))); }
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); } }; }
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