iOS：在运行时找不到NSURLSession类别方法 [英] iOS: NSURLSession category methods not being found at runtime

问题描述

我想在NSURLSession上创建一个类别。该应用程序编译好，但当我尝试调用类别方法时，我得到

I wanted to create a category on NSURLSession. The app compiles ok, but when I attempt to call the category methods I get

-[__NSCFURLSession doSomething]: unrecognized selector sent to instance 0xbf6b0f0
<unknown>:0: error: -[NSURLSession_UPnPTests testCategory] : -[__NSCFURLSession doSomething]: unrecognized selector sent to instance 0xbf6b0f0

非常奇怪，这是我为了显示问题而构建的测试类。 NSString上的类别工作正常，但NSURLSession上的类别无法在运行时找到该方法。我怀疑这是内部的东西。

Very strange, here is a test class I built to show the issue. The category on the NSString works fine, but the category on NSURLSession fails to find the method at runtime. I suspect this is something internal.

意见请： - ）

#import <XCTest/XCTest.h>

@interface NSString (test)
-(void) doSomethingHere;
@end

@implementation NSString (test)
-(void) doSomethingHere {
    NSLog(@"Hello string");
}
@end

@interface NSURLSession (test)
-(void) doSomething;
@end

@implementation NSURLSession (test)
-(void) doSomething {
    NSLog(@"Hello!!!!");
}
@end

@interface NSURLSession_UPnPTests : XCTestCase
@end

@implementation NSURLSession_UPnPTests
-(void) testCategory {
    [@"abc" doSomethingHere];
    NSURLSession *session = [NSURLSession sharedSession];
    [session doSomething];
}
@end

推荐答案

我在backgrounded NSURLSessionUploadTask 中获得了类似的结果，在 __ NSCFURLSessionUploadTask s > -URLSession：task：didCompleteWithError：委托回调。

I've had similar results with backgrounded NSURLSessionUploadTasks, which get deserialized as __NSCFURLSessionUploadTasks during the -URLSession:task:didCompleteWithError: delegate callback.

如果我是你，我会放弃这种方法，并使用构图（即在另一个对象中使 NSURLSession 成为一个ivar）。如果您需要使用 NSURLSession 存储一些信息，您可以将JSON编码的字典填充到 .sessionDescription 中。

If I were you, I'd give up on that approach, and use composition (i.e. make the NSURLSession an ivar in another object). If you need to store some info with the NSURLSession, you could stuff a JSON-encoded dictionary into the .sessionDescription.

以下是我过去为执行的代码：

#pragma mark - Storing an NSDictionary in NSURLSessionTask.description

// This lets us attach some arbitrary information to a NSURLSessionTask by JSON-encoding
// an NSDictionary, and storing it in the .description field.
//
// Attempts at creating subclasses or categories on NSURLSessionTask have not worked out,
// because the –URLSession:task:didCompleteWithError: callback passes an
// __NSCFURLSessionUploadTask as the task argument. This is the best solution I could
// come up with to store arbitray info with a task.

- (void)storeDictionary:(NSDictionary *)dict inDescriptionOfTask:(NSURLSessionTask *)task
{
    NSData *data = [NSJSONSerialization dataWithJSONObject:dict options:0 error:nil];
    NSString *stringRepresentation = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    [task setTaskDescription:stringRepresentation];
    [stringRepresentation release];
}

- (NSDictionary *)retrieveDictionaryFromDescriptionOfTask:(NSURLSessionTask *)task
{
    NSString *desc = [task taskDescription];
    if (![desc length]) {
        DDLogError(@"No description for %@", task);
        return nil;
    }
    NSData *data = [desc dataUsingEncoding:NSUTF8StringEncoding];
    NSDictionary *dict = (data ? (id)[NSJSONSerialization JSONObjectWithData:data options:0 error:nil] : nil);
    if (!dict) {
        DDLogError(@"Could not parse dictionary from task %@, description\n%@", task, desc);
    }
    return dict;
}

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