Question

First post here, so I hope it is detailed enough.

While developing an Iphone App I am confronted with some strange behavour. A member variable of a certain instance of my “WebserviceConnection” class seems to obtain the value I assign to another instances of the same class.

For illustration: This is en excerpt of my log. I assume the 0x000000 is an instance ID. The fourth response should be “<-: 1”.

2011-11-03 16:25:13.227 Dashboard[540:707] ->: 1, <WebserviceConnection: 0x11f950>
2011-11-03 16:25:13.256 Dashboard[540:707] ->: 0, <WebserviceConnection: 0x323db0>
2011-11-03 16:25:15.318 Dashboard[540:707] <-: 0, <WebserviceConnection: 0x323db0>
2011-11-03 16:25:15.325 Dashboard[540:707] <-: 0, <WebserviceConnection: 0x11f950>

The class is a NSUrlConnection delegate which exhibits this behavour when two connections are open at the same time.

This class: WebserviceConnection.h

(The ConnectionType is an enum)

#import "WebserviceConnection.h"
#import "WebserviceUtility.h"

@implementation WebserviceConnection

BOOL isCanceled;
NSDictionary *result;
ConnectionType connectionType;
id <WebserviceConnectionDelegate> delegate;

- (id)initWithDelegate:(id)webServiceDelegate connectionType:(ConnectionType) type {
    delegate = webServiceDelegate;
    connectionType = type;
    isCanceled = NO;
    NSLog(@"->: %i, %@", connectionType, self);
    return self;
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

    switch (connectionType) {
        case GetAllAlerts:
            result = [WebserviceUtility getJsonFromData:data]; 
            break;
        case GetServerAlerts:
            result = [WebserviceUtility getJsonFromData:data]; 
            break;
        case GetServers:
            result = [WebserviceUtility getJsonFromData:data]; 
            break;
        default:
            result = nil;
            break;
    }
}

- (void)displayErrorAlert {
    UIAlertView *errorMessage = [[UIAlertView alloc] initWithTitle:@"Fout" message:@"Verbinding met webservice niet mogelijk" delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
    [errorMessage show];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    if(!isCanceled) {
        @try {
            [delegate connection:connection ofType:connectionType didFinishWithError: [NSDictionary dictionaryWithObject:@"error" forKey:@"WebserverConnectionFailed"]];
        }
        @catch (NSException *e) {}
        @finally {}
        [self displayErrorAlert];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"<-: %i, %@", connectionType, self);
    if(!isCanceled) {
        [delegate connection:connection ofType:connectionType didFinishWithResult:result];
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
    NSURLCredential *credential = [WebserviceUtility getCredentials];
    if ([challenge previousFailureCount] == 0) {
        [[challenge sender] useCredential:credential
               forAuthenticationChallenge:challenge];
    }
    else {
        [delegate connection:connection ofType:connectionType didFinishWithError: [NSDictionary dictionaryWithObject:@"error" forKey:@"WebserverConnectionFailed"]];
        [self displayErrorAlert];

    }
}

- (void)delegateDidDealloc {
    NSLog(@"!!: %i, %@", connectionType, self);
    isCanceled = YES;
}

@end

Used like this:

- (void) getAllAlerts {
    NSURLRequest *request = [WebserviceUtility getRequestForPath:@"/dashboard/DashboardAppleConnector.asmx/GetActiveAlerts"];
    webserviceConnection = [[WebserviceConnection alloc] initWithDelegate:self connectionType:GetAllAlerts];
    connection = [[NSURLConnection alloc] initWithRequest:request delegate: webserviceConnection];
}

When another ViewController with its own webserviceConnection instance uses its instance (similar to getAllAlerts) all goed pearshaped!

Any thoughts anyone?

Regards,
Bert

Answer 1

It looks like the problem is happening because of the way you are declaring your variables like connectionType. If you want them to be declared as instance variables, you should be putting them in the interface declaration:

@interface WebServiceConnection {
    BOOL isCanceled;
    NSDictionary *result;
    ConnectionType connectionType;
    id <WebserviceConnectionDelegate> delegate;
}
@end

By declaring them in the @implementation block you are actually creating global variables, not instance variables.

See this SO post for more information