NSURLConnection委托方法：didReceiveData没有被调用...为什么？ （iPhone SDK）

Question

示例代码：

-(void)ConnectWithRequest:(NSMutableURLRequest*)req{

if(![req isEqual:theRequest]){
    [req retain];
    [theRequest release];
    theRequest = req;
}

XMLConnection = [[XMLWebServiceConnection alloc]init];  
Connection=[[NSURLConnection alloc]initWithRequest:theRequest delegate:XMLConnection];
}

在XMLConnection类中，我实现了NSURLConnection委托方法：

-(id)init{

    if(self=[super init]){
        receivedData = [[NSMutableData alloc]init]; //member of a class
    }
    return self;
}


- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
    [receivedData release];
}

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

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

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

    NSString *theXML = [[NSString alloc] initWithBytes: [receivedData mutableBytes] length:[receivedData length] encoding:NSUTF8StringEncoding];

    NSLog(@"\nResponse printed :\n\n\n %@\n",theXML);

    [theXML release];

}

当我运行此代码时，

方法：

connection:(NSURLConnection *)connection didReceiveData:(NSData *)data

没有被召唤，出现这种情况的原因是什么？如何解决这个问题??

---

由于