NSClassFromString(MyClassName) 比调用 MyClass 的 class function

Question

i got a UIViewCustom Class with 7 childs. each of the childs got their own class functions for helping initiating

+(int) minHeight;
+(int) minWidth;

in a UITableView i select one of the classes and the function "-insertNewObjectWithClassName:(NSString*)childClassName" gets called.

In that function i want to create the instance depending to the classname, so i tryed

Class *class = NSClassFromString(childClassName);
CGRect frame = CGRectMake(0, 0, [class minWidth], [class minWidth])
MotherClass *view = [[class alloc] initWithFrame:frame];

But unfortunately the static function can't be called.

Is there a way, to say the compiler that class is not just a Class but also a MotherClass to tell him the function?

thank you very much!

EDIT: Warning: Semantic Issue: Method '-minWidth' not found (return type defaults to 'id')

SOLUTION: Class class instead of Class *class

Answer 1

Something must be wrong elsewhere, eg the name of the class you are passing. This demo program works as expected (layout compacted for brevity):

#import <Foundation/Foundation.h>

@interface MyChild
+ (int) minHeight;
+ (int) minWidth;
@end

@implementation MyChild
+ (int) minHeight { return 100; }
+ (int) minWidth { return 300; }
@end

int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSString *className = [NSString stringWithString: @"MyChild"];
    Class theClass = NSClassFromString(className);
    NSLog(@"%d %d", [theClass minHeight], [theClass minWidth]);

    [pool drain];
    return 0;
}

Output:

2011-08-10 18:15:13.877 ClassMethods[5953:707] 100 300

Answer 2

This answer seems related: How do I call +class methods in Objective C without referencing the class?

You can define an interface that has the methods you want to call and then have something like:

Class<MyCoolView> class = NSClassFromString(childClassName);
CGRect frame = CGRectMake(0, 0, [class getMinWidth], [class getMinWidth]);
MotherClass *view = [[class alloc] initWithFrame:frame];

This should eliminate compiler warnings and make your code typesafe.

Answer 3

• Objective-C does not have static functions. It has Methods; class or instance.

• do not prefix methods with get ; that is reserved for a particular use case, this isn't it.

Your code looks more or less correct. Are you sure that childClassName contains the correct name of the class?

In general, your question indicates a bit of a lack of an understanding of Objective-C or, at the least, an assumption that Obj-C works like C++ (or Java). I would suggest perusing the language documentation as it will answer various meta questions that will make all of this pretty clear.