iOS 5.0 respondsToSelector 总是在 NSOperation 中返回 false

Question

我在将云数据库服务的静态库移植到 ARC 时遇到问题。

我已经到了它编译和运行的阶段，但它永远不会回调委托。

我有 2 个类，一个代理类和一个 APIOperation。

APIOperation 是 NSOperation 的子类，它使用 NSURLConnection 从 Web API 获取数据。

代理有一个 NSOperationQueue，基本上是所有 APIOperation 调用的委托。

使用模型如下：

• 用户类创建代理对象的实例。
• Proxy实例化APIOperation对象并将其添加到NSOperationQueue
• 创建NSURLConnection
• APIOperation在connectionDidFinishLoading上
  • 解析响应，然后通过 NSInitation 将其传回代理类。
  • 代理类调用委托（用户类）并传回 API 响应。

代码如下：

代理类：

@implementation theProxy

@synthesize callbackSelector,delegate,opQueue;

-(theProxy*)init{
    opQueue = [[NSOperationQueue alloc]init];
    return self;
}

- (void) apiOperation:(APIOperation*)operation didCompleteWithResult:(NSArray*)theResult{
    SEL selector = [operation callbackSelector];
    if ([delegate respondsToSelector:selector]) {
    NSInvocation* inv = [NSInvocation invocationWithMethodSignature:[[delegate class] instanceMethodSignatureForSelector:selector]];
    [inv setTarget:delegate];
    [inv setSelector:selector];
    theProxy* tmp = self;
    [inv setArgument:&tmp atIndex:2];
    [inv setArgument:&operation atIndex:3];
    [inv setArgument:&theResult atIndex:4];
    [inv invoke];        
}

}

- (void) apiOperation:(APIOperation*)operation didFailWithError:(NSString*)theError{
if ([delegate respondsToSelector:@selector(API:apiOperation:didFailWithError:)]) {
    [delegate API:self apiOperation:operation didFailWithError:theError];
}
}

-(void)cancelAllOperations{
[opQueue cancelAllOperations];
}

- (void)dealloc
{
[opQueue cancelAllOperations];
[opQueue release], opQueue = nil;
delegate = nil;
//[delegate release];  delegate should not be retained.

[super dealloc];
}

APIOperation类（大大简化）：

@implementation APIOperation
@synthesize delegate,APIKey,secretKey,debugMode,callbackSelector,successCallbackMethodSignature,errorCallbackMethodSignature,delegateCallbackMethodSignature,tag,APIServer,requestProcessingTime,requestReceivedTime,responseCode,responseMessage,timestamp,requestRoundTripTime,requestStartMicroTime,useSSL;

-(void) main{
    receivedData = [NSMutableData data];
    connFinished = NO;
    // create the connection with the request
    // and start loading the data
    theConnection=[[NSURLConnection alloc] initWithRequest:[self buildRequest] delegate:self];
    if (theConnection) {

        do {
            [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
            } while (!connFinished);
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{

    id pList = [NSPropertyListSerialization propertyListFromData:receivedData mutabilityOption:NSPropertyListImmutable format:&format errorDescription:&errorStr];

    theResponse = (NSDictionary*) pList;

    if ([delegate respondsToSelector:@selector(apiOperation: didCompleteWithResult:)]) {

        NSArray* theResultsArray = [theResponse objectForKey:@"payload"];

        NSInvocation *inv = [NSInvocation invocationWithMethodSignature:successCallbackMethodSignature];
        [inv setTarget:delegate];
        [inv setSelector:@selector(apiOperation: didCompleteWithResult:)];
        KSAPIOperation* tmp = self;
        [inv setArgument:&tmp atIndex:2];
        [inv setArgument:&theResultsArray atIndex:3];
        [inv performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:YES];

    }       
}
@end

现在正如我所说，直到connectionDidfinishLoading中的“if([delegate respondsToSelector...”行。此时它总是返回 false。现在假设这个与 ARC 有关，我检查了委托不为 null 并且值存在，委托属性也在 APIOperation.h 中声明为：

@property (unsafe_unretained) id<KSAPIOperationDelegate,NSObject> delegate;

如果我删除 respondsToSelector 检查，则应用程序main() 中崩溃并出现以下回溯：

#0  0x0156b09b in objc_msgSend ()
#1  0xbfffde10 in ?? ()
#2  0x0132d437 in -[NSInvocation invoke] ()
#3  0x013c8e72 in -[NSObject performSelector:withObject:] ()
#4  0x009369ef in __NSThreadPerformPerform ()
#5  0x0139b97f in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#6  0x012feb73 in __CFRunLoopDoSources0 ()
#7  0x012fe454 in __CFRunLoopRun ()
#8  0x012fddb4 in CFRunLoopRunSpecific ()
#9  0x012fdccb in CFRunLoopRunInMode ()
#10 0x012b0879 in GSEventRunModal ()
#11 0x012b093e in GSEventRun ()
#12 0x0001ea9b in UIApplicationMain ()
#13 0x00002a58 in main (argc=1, argv=0xbfffed50) at /Users/MikeW/Desktop/ARC test proj/lib1.0Test/lib1/main.m:16
#14 0x000029b5 in start ()

感谢您提供的任何帮助，

。

谢谢迈克

Answer 1

这与ARC没有任何关系。

如果它报告它没有响应选择器，那么它就不会。弄清楚这一点。您很可能在选择器中出现拼写错误（例如，它们区分大小写）。或者委托实际上并不是您想象的那样。

顺便说一句，我会从选择器中删除空格，例如 @selector(apiOperation: didCompleteWithResult:) 看起来是错误的，即使编译器喜欢它。

Answer 2

正如大卫所说，这是代表被释放的问题。

通过简单地将属性设置为“(strong)”而不是 unsafe_unretained 或 __weak 就解决了这个问题。

@property (strong) id<KSAPIOperationDelegate,NSObject> delegate;