calling selector with two arguments on NSThread issue

Question

I'd like to make a Thread with multiple arguments. Is it possible? I have the function:

-(void) loginWithUser:(NSString *) user password:(NSString *) password {
}

And I want to call this function as a selector:

[NSThread detachNewThreadSelector:@selector(loginWithUser:user:password:) toTarget:self withObject:@"someusername" withObject:@"somepassword"]; // this is wrong

How to pass two arguments on withObject parameter on this detachNewThreadSelect function?

Is it possible?

Answer 1

You need to pass the extra parameters in an object passed to withObject like so:

NSDictionary *extraParams = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"user",@"password",nil] andKeys:[NSArray arrayWithObjects:@"valueForUser",@"valueForPassword",nil]]

[NSThread detachNewThreadSelector:@selector(loginWithUser:) toTarget:self withObject:extraParams]; 

Answer 2

This is off the top of my head, untested:

NSThread+ManyObjects.h:

@interface NSThread (ManyObjects)

+ (void)detachNewThreadSelector:(SEL)aSelector
                       toTarget:(id)aTarget 
                     withObject:(id)anArgument
                      andObject:(id)anotherArgument;

@end

NSThread+ManyObjects.m:

@implementation NSThread (ManyObjects)

+ (void)detachNewThreadSelector:(SEL)aSelector
                       toTarget:(id)aTarget 
                     withObject:(id)anArgument
                      andObject:(id)anotherArgument
{
    NSMethodSignature *signature = [aTarget methodSignatureForSelector:aSelector];
    if (!signature) return;

    NSInvocation* invocation = [NSInvocation invocationWithMethodSignature:signature];
    [invocation setTarget:aTarget];
    [invocation setSelector:aSelector];
    [invocation setArgument:&anArgument atIndex:2];
    [invocation setArgument:&anotherArgument atIndex:3];
    [invocation retainArguments];

    [self detachNewThreadSelector:@selector(invoke) toTarget:invocation withObject:nil];
}

@end

And then you can import NSThread+ManyObjects and call

[NSThread detachNewThreadSelector:@selector(loginWithUser:user:password:) toTarget:self withObject:@"someusername" andObject:@"somepassword"];

Answer 3

Wrap your selected method with an auxiliary wrapping method, "wrappingMethod", that processes an NSArray of inputs to suit your own method before calling your own method within wrappingMethod. Now detach an NSThread that selects your all new wrappingMethod and takes the NSArray instance for withObject.

Aside: Having a wrapper here can be particularly helpful if your original method takes one or more primitive types as input and you then have to work with NSNumber or NSStrings, say, to satisfy NSThread.

Answer 4

An update to ennuikiller's nice answer:

NSDictionary* params = [NSDictionary dictionaryWithObjectsAndKeys:@"IMG_URL_VALUE",@"img_url",@"PARAM2_VALUE", @"param2", nil];

[NSThread detachNewThreadSelector:@selector(loadImage:) toTarget:self withObject:params];