Re: Constructing class names dynamically
Re: Constructing class names dynamically
- Subject: Re: Constructing class names dynamically
- From: "Mohan Parthasarathy" <email@hidden>
- Date: Thu, 15 Jan 2009 11:10:48 -0800
Hi,
Thanks a bunch.. It really helped me to debug the problem.
-mohan
On Thu, Jan 15, 2009 at 10:48 AM, Andy Lee <email@hidden> wrote:
> Unless you're explicitly loading in bundles or plugins, I wouldn't think
> you need to force the class to be loaded. I just tested a call to
> NSClassFromString(nameOfTestClass) as the first line of my main() function
> and it worked.
>
> In situations like this I try to question my most petty assumptions.
> Suppose one of the classes in question is named SomeClass. I would add a
> couple of lines like this to make sure the string is what you think it is
> and that SomeClass has actually been compiled into your application (maybe
> you accidentally removed it from the target in Xcode?):
>
> NSLog(@"clsName is [%@]", clsName);
> NSLog(@"the [%@] class is definitely loaded", [SomeClass class]);
>
> When I NSLog, I often put square brackets around strings in case there are
> spaces or newlines that I might not notice.
>
> --Andy
>
> On Jan 15, 2009, at 1:27 PM, Mohan Parthasarathy wrote:
>
> Hi,
>
> I have tried this to make sure that the class is loaded, but not working:
>
> [[NSBundle mainBundle] classNamed:clsName];
> [self loadBundleForClass:clsName];
> Class cls = NSClassFromString(clsName);
>
> I still get nil.. What am i missing ?
>
> thanks
> mohan
>
> On Thu, Jan 15, 2009 at 9:17 AM, Mohan Parthasarathy <email@hidden
> >wrote:
>
> Both of the methods return nil and as per the document it says "Class is
>
> not loaded". Is there a compile time option to load the classes or only way
>
> to do it as at runtime..
>
>
> thanks
>
> mohan
>
>
>
>
> On Wed, Jan 14, 2009 at 6:46 AM, Adam Venturella <email@hidden
> >wrote:
>
>
> The output is the same, but there is also:
>
> #import <objc/runtime.h>
>
> objc_getClass([myString UTF8String]);
>
>
> I am going to guess that NSClassFromString(myString) is probably using
>
> objc_getClass(), maybe not. I didn't know NSClassFromString existed
>
> though, so I am switching to that instead of using the runtime.h
>
> function.
>
>
>
>
>
> On Tue, Jan 13, 2009 at 8:45 PM, Mohan Parthasarathy <email@hidden>
>
> wrote:
>
> On Tue, Jan 13, 2009 at 8:06 PM, Ken Thomases <email@hidden>
>
> wrote:
>
>
> On Jan 13, 2009, at 3:33 PM, Jean-Daniel Dupas wrote:
>
>
> he is just talking about class name, not class.
>
>
> NSClassFromString() is probably what you're looking for.
>
>
> NSMutableString *clsName = derive class name from the entry.
>
>
> Class cls = NSClassFromString(clsName);
>
>
> id<YouProtocol> instance = [[cls alloc] init];
>
>
>
> I'll just add the following:
>
>
> If you don't need such complete flexibility -- for example, if you're
>
> selecting from a fixed set of classes by some tag -- then you don't
>
> need to
>
> compute a class name and look up the class that way.
>
>
> Classes are objects and so they can be stored in collections. For
>
> example,
>
> you could have a lookup dictionary that mapped from keys to class
>
> objects.
>
> You would construct the dictionary like this:
>
>
> [NSDictionary dictionaryWithObjectsAndKeys:
>
> [SomeClass class], "key1",
>
> [OtherClass class], "key2",
>
> [ThirdClass class], "key3",
>
> // ... etc.
>
> nil];
>
>
> This adds a small amount of safety in the same way that
>
> statically-specified stuff generally does. For example, the compiler
>
> will
>
> catch typos in class names.
>
>
>
> Thanks for this suggestion. This looks fairly clean except that the
>
> space is
>
> allocated at the beginning. This may not be a big deal in some cases. In
>
> the
>
> other way, you allocate space and insert in the dictionary only when
>
> needed.
>
> Also, eventually i need the real object instances inserted in the
>
> dictionary.
>
>
> -mohan
>
>
>
> -mohan
>
>
>
>
> Cheers,
>
> Ken
>
>
>
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