NSInvocation usage example.

gistfile1.m

// Omitting the ownership qualification here can lead to a EXC_BAD_ACCESS exception in ARC enabled projects.
__weak id returnValue = nil;

SEL selector = @selector(colorFromString:);
NSString *valueString = @"0.2 0.2 0.2 1.0";

// Create and configure the NSInvocation object.
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[target methodSignatureForSelector:selector]];
invocation.selector = selector;
invocation.target = target;
[invocation setArgument:&valueString atIndex:2];
[invocation invoke];
[invocation getReturnValue:&returnValue];