iOS4 Implementation of -[NSURLConnection sendAsync

问题:

How can I implement -[NSURLConnection sendAsynchronousRequest:queue:completionHandler:] for iOS < 5?

#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_5_0

#import <objc/runtime.h>
#import "NSURLConnection+iOS4.h"

// Dynamically add -[NSURLConnection sendAsynchronousRequest:queue:completionHandler:].
void *sendAsynchronousRequest4(id self, SEL _cmd, NSURLRequest *request, NSOperationQueue *queue, void (^handler)(NSURLResponse*, NSData*, NSError*));
void *sendAsynchronousRequest4(id self, SEL _cmd, NSURLRequest *request, NSOperationQueue *queue, void (^handler)(NSURLResponse*, NSData*, NSError*)) {

    // How should we implement this?

}

@implementation NSURLConnection (SendAsync)

+ (void)load {
    SEL sendAsyncSelector = @selector(sendAsynchronousRequest:queue:completionHandler:);
    if (![NSURLConnection instancesRespondToSelector:]) {
        class_addMethod([self class], sendAsyncSelector, (IMP)sendAsynchronousRequest4, "v@:@@@");
    }
}

@end

#endif

回答1:

// NSURLConnection+SendAsync.h

#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_5_0

#import <Foundation/Foundation.h>

@interface NSURLConnection (SendAsync)

@end

#endif


// NSURLConnection+SendAsync.m

#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_5_0

typedef void (^URLConnectionCompletionHandler)(NSURLResponse *response, NSData *data, NSError *error);

@interface URLConnectionDelegate : NSObject <NSURLConnectionDataDelegate>

@property (nonatomic, strong) NSURLResponse *response;
@property (nonatomic, strong) NSMutableData *data;
@property (nonatomic, strong) NSOperationQueue *queue;
@property (nonatomic, copy) URLConnectionCompletionHandler handler;

@end 

@implementation URLConnectionDelegate 

@synthesize response;
@synthesize data;
@synthesize queue;
@synthesize handler;

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)theResponse {
    self.response = theResponse;
    [data setLength:0]; // reset data
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)theData {
    [data appendData:theData]; // append incoming data
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    self.data = nil;
    if (handler) { [queue addOperationWithBlock:^{ handler(response, nil, error); }]; }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    // TODO: Are we passing the arguments to the block correctly? Should we copy them?
    if (handler) { [queue addOperationWithBlock:^{ handler(response, data, nil); }]; }
}

@end

#import <objc/runtime.h>
#import "NSURLConnection+SendAsync.h"

// Dynamically add @property (nonatomic,readonly) UIViewController *presentingViewController.
void sendAsynchronousRequest4(id self, SEL _cmd, NSURLRequest *request, NSOperationQueue *queue,
                              URLConnectionCompletionHandler handler);
void sendAsynchronousRequest4(id self, SEL _cmd, NSURLRequest *request, NSOperationQueue *queue,
                              URLConnectionCompletionHandler handler) {

    URLConnectionDelegate *connectionDelegate = [[URLConnectionDelegate alloc] init];
    connectionDelegate.data = [NSMutableData data];
    connectionDelegate.queue = queue;
    connectionDelegate.handler = handler;
    NSURLConnection *connection = [NSURLConnection connectionWithRequest:request
                                                                delegate:connectionDelegate];
    NSAssert(connection, nil);
}

@implementation NSURLConnection (SendAsync)

+ (void)load {
    SEL sendAsyncSelector = @selector(sendAsynchronousRequest:queue:completionHandler:);
    if (![NSURLConnection instancesRespondToSelector:sendAsyncSelector]) {
        class_addMethod(object_getClass([self class]),
                        sendAsyncSelector, (IMP)sendAsynchronousRequest4, "v@:@@@");
    }
}

@end

#endif

回答2:

I typically make a sub-class of NSOperation and do the sync request inside the main method of the operation. To invoke the operation I create an instance of the sub-class and throw it onto a queue (not the main thread). Then when the operation completes it either calls a delegate with the received data or posts a notification via NSNotificationCenter.

回答3:

I would go with an already built framework like ASIHTTPRequest (No longer being developed, but still very good) or RestKit (I've never used it before but heard it's decent). These will give you the same functionality (asyncrhonous http requests) across different versions of the OS.

ifdefs aren't the way to go since they're done at compile time and you won't be compiling separate versions of the app for each platform.

You could probably do some shenanigans at runtime to get it to work but it seems like more trouble than it's worth.