iphone - NSURLConnection 和中央调度

Question

是否建议将 NSUrlConnection 包装在 gcd 样式 block 中并在 low_priority 队列上运行它？

我需要确保我的连接不会发生在主线程上，并且连接需要异步。我还需要同时发出多个请求。

如果我采用 gcd 路线，我不确定 NSUrlConnectionDelegate 方法会在哪个线程上调用。

NSURLConnection 依赖于委托(delegate)，因此一旦连接完成，无论处理它的包装类都需要调用其调用者。我不确定如何处理连接工作启动/完成时调用的所有各种回调:

- (void)connection:(NSURLConnection *)aConnection didReceiveResponse:(NSURLResponse *)response;
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)incrementalData;
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

我应该只调用同步版本但包裹在 gcd block 中吗？如果我想取消通话，请使用“dispatch_suspend”？

dispatch_async(queue,^{
      NSString* result = [self mySynchronousHttp:someURLToInvoke];
      });

// If I need to cancel
dispatch_suspend(queue);

Answer 1

我推荐你看WWDC Sessions关于iPhone OS中的网络应用。

• WWDC 2010 第 207 场 session - 适用于 iPhone 操作系统的网络应用程序，第 1 部分
• WWDC 2010 第 208 场 session - 适用于 iPhone 操作系统的网络应用程序，第 2 部分

讲师说

"Threads Are Evil™"

对于网络编程，推荐使用带有RunLoop的异步网络编程。使用后台线程(Grand Central Dispatch Concurrent Queue)进行线程安全的数据处理，而不是进行网络编程。

顺便说一句，Blocks 和 Grand Central Dispatch session 也值得一看。

• WWDC 2010 第 206 场 session - 介绍 iPhone 上的 Blocks 和 Grand Central Dispatch
• WWDC 2010 第 211 场 session - 使用 Grand Central Dispatch 简化 iPhone 应用程序开发

我为异步 NSURLConnection 编写了一个包装类。

<小时/>

AsyncURLConnection.h

#import <Foundation/Foundation.h>

typedef void (^completeBlock_t)(NSData *data);
typedef void (^errorBlock_t)(NSError *error);

@interface AsyncURLConnection : NSObject
{
    NSMutableData *data_;
    completeBlock_t completeBlock_;
    errorBlock_t errorBlock_;
}

+ (id)request:(NSString *)requestUrl completeBlock:(completeBlock_t)completeBlock errorBlock:(errorBlock_t)errorBlock;
- (id)initWithRequest:(NSString *)requestUrl completeBlock:(completeBlock_t)completeBlock errorBlock:(errorBlock_t)errorBlock;
@end

<小时/>

AsyncURLConnection.m

#import "AsyncURLConnection.h"

@implementation AsyncURLConnection

+ (id)request:(NSString *)requestUrl completeBlock:(completeBlock_t)completeBlock errorBlock:(errorBlock_t)errorBlock
{
    return [[[self alloc] initWithRequest:requestUrl
        completeBlock:completeBlock errorBlock:errorBlock] autorelease];
}

- (id)initWithRequest:(NSString *)requestUrl completeBlock:(completeBlock_t)completeBlock errorBlock:(errorBlock_t)errorBlock
{

    if ((self=[super init])) {
        data_ = [[NSMutableData alloc] init];

        completeBlock_ = [completeBlock copy];
        errorBlock_ = [errorBlock copy];

        NSURL *url = [NSURL URLWithString:requestUrl];
        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        [NSURLConnection connectionWithRequest:request delegate:self];
    }

    return self;
}

- (void)dealloc
{
    [data_ release];

    [completeBlock_ release];
    [errorBlock_ release];
    [super dealloc];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [data_ setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [data_ appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    completeBlock_(data_);
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    errorBlock_(error);
}

@end

<小时/>

如何使用AsyncURLConnection类。

/*
 * AsyncURLConnection -request:completeBlock:errorBlock: have to be called
 * from Main Thread because it is required to use asynchronous API with RunLoop.
 */

[AsyncURLConnection request:url completeBlock:^(NSData *data) {

    /* success! */

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        /* process downloaded data in Concurrent Queue */

        dispatch_async(dispatch_get_main_queue(), ^{

            /* update UI on Main Thread */

        });
    });

} errorBlock:^(NSError *error) {

    /* error! */

}];