Is there JavaScript apply like method in objective-c?

Question

So basically I'm implementing the typical way to handle JavaScript calls in objc using window.location="myobj:mymethod:myarg:myotherarg", however, I'm wondering if there is a way to apply an array of arguments to a method, similar to how you can in JavaScript.

Typically I've been doing

-(void) mymethod:(NSArray*) arr{
    //method knows how many arguments it takes and what they mean at each index
}

I'd prefer to do:

-(void) mymethod:(NSString*) myarg myOtherArg: (NSString*) myotherarg{
    //do stuff
}

and have a method like this:

+(void) callMethod:(NSString*)selectorName withArgs: (NSArray*)args onObject:(id) obj{
    //implementation
}
[JEHelpers callMethod:selector withArgs:someArrayOfArgs onObject:myapp]

is this possible?

Answer 1

If you know that no method will take more than two arguments, you could use performSelector:withObject:withObject: to do these calls. If the method takes less than two arguments, the unused withObject: fields will be ignored.

+ (id)callMethod:(NSString *)selectorName withArgs:(NSArray *)args onObject:(id)obj {
    id arg1 = nil, arg2 = nil;
    if([args count]) {
        arg1 = [args objectAtIndex:0];
        if([args count] > 1])
           arg2 = [args objectAtIndex:1];
    }
    return [obj performSelector:NSSelectorFromString(selectorName)
                     withObject:arg1 withObject:arg2];
}

If there could be more than two arguments, you will have to use NSInvocation . This class lets you construct a message by passing the various arguments and defining the selector and object, then send the message and get the result.

+ (id)callMethod:(NSString *)selectorName withArgs:(NSArray *)args onObject:(id)obj {
    SEL sel = NSSelectorFromString(selectorName);
    NSMethodSignature *signature = [obj methodSignatureForSelector:sel];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
    [invocation setSelector:sel];
    [invocation setTarget:obj];
    NSUInteger index = 2;
    for(id arg in args) {
        [invocation setArgument:&arg atIndex:index];
        ++index;
    }
    id result;
    [invocation setReturnValue:&result];
    [invocation invoke];
    return result;
}

Answer 2

I'm not sure I entirely understand the question (I don't know JavaScript well). However, you can use NSInvocation to send arbitrary messages to any object. Something like this:

+(void) callMethod:(NSString*)selectorName withArgs: (NSArray*)args onObject:(id) obj
{
    SEL selector = NSSelectorFromString(selectorName);
    if (![obj respondsToSelector:selector]) {
        // Object doesn't respond to selector, so do something else/handle the error
    }
    NSMethodSignature *methodSignature = [obj methodSignatureForSelector:selector];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
    [invocation setTarget:obj];
    [invocation setSelector:selector];
    for (NSUInteger i=0; i<[args count]; i++) {
        id argument = [args objectAtIndex:i];
        [invocation setArgument:&argument atIndex:i+2]; // Arg 0 is self, arg 1 is _cmd
    }
    id result;
    [invocation setReturnValue:&result];
    [invocation invoke];
}

Answer 3

You might want to look into NSInvocation. Specifically, you want to build an NSInvocation with selectorName's method signature (NSObject -methodSignatureForSelector:), then set the selector, target, and arguments. Keep in mind: you should check for the argument types (NSMethodSignature -getArgumentTypeAtIndex:, is it equal to '@'), and the arguments you are passing are indexed starting with 2 (because 0 and 1 are the object's self and the method selector).

I'm not saying this is a good idea, btw; there are very few cases where this approach is warranted.

Answer 4

It's a bit clumsy but it is possible:

- (id)method:(NSString *)arg1, ... {
  va_list args;
  va_start(args, arg1);
  for (NSString *a = arg1; a!= nil; a= va_arg(args, NSString*)) {
    // do stuff
  }
}

Conventionally arg1 would be a string that defines the data types and number of extra parameters.

You'd call it like this:

[self method:@"5", @"4", @"3", @"2", @"1"];

Your array method is probably clearer for most purposes.