Question

Given the following code:

for (id object in anArray){
    if ([object isKindOfClass:[ClassOne class]]){
       ClassOne *myObj = [[ClassOne alloc] init];
    }else if ([object isKindOfClass:[ClassTwo class]]){
       ClassTwo *myObj = [[ClassTwo alloc] init];
    }
    myObj.property = TRUE;
}

the compiler will raise an error regarding myObj (undeclared identifier), which is somehow obvious (“what should I do if both conditions will be false?”). That means I have to define the object before the if-else block, but which type of object I have to use? If I use id there will be errors on myObj.property = TRUE;, if I use ClassOne or ClassTwo there will be some warnings regarding incompatible pointer assignment. Should I use some other way instead of the given code?

Thank you.

(note: the snippet was written without using syntax checking or testing it, so it may contains errors)

Answer 1

How about a protocol?

@protocol MyProtocol

@property (assign, nonatomic) BOOL myProperty;

@end

Then:

for (id anObject in anArray){
    if ([anObject conformsToProtocol:@protocol(MyProtocol)]) {
        Class clazz = [anObject class];
        id<MyProtocol>  myObject = [[clazz alloc] init];
        myObject.myProperty = YES;
    }
}

This is the cleanest and shortest solution I can think of. You won’t need to cast, instead you will harness the power of objective-c’s dynamic binding. You won’t have to add too many if-else statements. Instead you just make sure the object that comes in, conforms to your protocol.