iOS網路: NSURLConnection進行同步下載

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　　通過 NSURLConnection 的 sendSynchronousRequest:returningResponse:error: 方法建立一 個同步的網路連接。這個方法將會返回一個 NSData 類型的資料  　　在建立一個同步的網路連接的時候我們需要明白一點,並不是是我們 的這個同步串連一定會堵塞我們的主線程,如果這個同步的串連是建立在主線程上的,那麼 這種情況下是會堵塞我們的主線程的,其他的情況下是不一定會堵塞我們的主線程的。如果你在 GCD 的全域並發隊列上初始化了一個同步的串連,你其實並不會堵塞我們的主線程的。 

 

例子:

- (void)sendSynNetwork{    NSLog(@"Wo are here...");    NSString *urlString = @"http://www.baudu.com";    NSURL *url = [NSURL URLWithString:urlString];    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0f];    //同步沒有block    //這樣解決比較方便    NSURLResponse *response = nil;    NSError *error = nil;    NSLog(@"開始同步請求");    NSData *data = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];    if ([data length] > 0 && error == nil){        NSLog(@"%lu bytes of data was returned.", (unsigned long)[data length]); }    else if ([data length] == 0 && error == nil){        NSLog(@"No data was returned.");    }    else if (error != nil){        NSLog(@"Error happened = %@", error);    }    NSLog(@"We are done.");}

Wo are here...

開始同步請求

8875 bytes of data was returned.

We are done.

 通過上面的代碼我們不難發現,其實我們的主線程是一直堵塞著,也就是說段代碼是一行一行執行的。 下面讓我們看一下,當我們建立一個同步的串連,並且添加到 GCD 的隊列池中去,我們又會發現什麼: 

 

//簡單的同步請求- (void)sendSynNetwork{    NSLog(@"Wo are here...");    NSString *urlString = @"http://www.baudu.com";    NSURL *url = [NSURL URLWithString:urlString];    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0f];    dispatch_queue_t dispatchQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    dispatch_async(dispatchQueue, ^{        //同步沒有block        //這樣解決比較方便        NSURLResponse *response = nil;        NSError *error = nil;        NSLog(@"開始同步請求");        NSData *data = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];        if ([data length] > 0 && error == nil){            NSLog(@"%lu bytes of data was returned.", (unsigned long)[data length]); }        else if ([data length] == 0 && error == nil){            NSLog(@"No data was returned.");        }        else if (error != nil){            NSLog(@"Error happened = %@", error);        }            });   NSLog(@"We are done.");}

Wo are here...

We are done.

開始同步請求

9138 bytes of data was returned.

 

 

 

 

iOS網路: NSURLConnection進行同步下載