iOS Best way to access all properties of an object whose names begin with a string?

[moonman239]

Suppose I have a piece of code like this:

Person *JohnDoe;
Person *JaneDoe;
Person *RichardRowe;
JohnDoe.friends = [NSArray arrayWithObjects:JaneDoe,RichardRowe];

Now suppose that I want to access the variable in JohnDoe.friends whose name begins with the letter J. How do I do that?

 

[moonman239]

I think I found the answer.

1) All NSArrays have a method that is named filteredArrayUsingPredicate. This method returns objects that meet the condition or set of conditions set forth in the predicate that is passed to the method.

2) Each NSObject has a description string that contains the name of the variable. This is normally used during development for making sure a variable has a value, but according to the author of the 1st answer on this page I can use it for other reasons, mine included.

 

[PhoneyDeveloper]

Using description for anything other than debugging is frowned upon. Also, your Person description method won't be useful unless you write it.

Use the name property directly in your predicate.

 

[ArtOfWarfare]

I agree with PhoneyDeveloper - use the name property of Person as your predicate. If Person doesn't have a name property, make it one and use it.

 

[moonman239]

I was just using a Person object as an example. Here's a better example to demonstrate what I wanted to do:

NSObject *anObject;
NSObject *anotherObject;
-(void-)viewDidLoad
{
NSObject *objectImThinkingOf = [self objectWhoseNameContainsLetter:@"r"];
}

-(NSObject *)objectWhoseNameContainsLetter:(NSString *)theLetter
{
// Code that is used to find the object to use.
}

 

[ArtOfWarfare]

The major difference between the two pieces of code you gave us has nothing to do with Person - it's actually the fact you went from having an NSArray to not having anything.

To do that, you'll want to look into the objc-runtime header.

Here's some incomplete code to help you get started...

#import <objc/objc-runtime.h>

    unsigned int outCount;
    Ivar *ivars = class_copyIvarList(self.class, outCount);
    if (ivars) {
        for (int i = 0; i < outCount; i++) {
            Ivar ivar = ivars[i];
            const char *ivarName = ivar_getName(ivar);
            NSString *ivarNameString = [NSString stringWithCString:ivarName encoding:NSASCIIStringEncoding];
            // You now have the name of the ivar as an NSString. You can compare it against whatever and decide what you want to do with it from here.
        }
    }

 

[moonman239]

The major difference between the two pieces of code you gave us has nothing to do with Person - it's actually the fact you went from having an NSArray to not having anything.

To do that, you'll want to look into the objc-runtime header.

Here's some incomplete code to help you get started...

#import <objc/objc-runtime.h>

    unsigned int outCount;
    Ivar *ivars = class_copyIvarList(self.class, outCount);
    if (ivars) {
        for (int i = 0; i < outCount; i++) {
            Ivar ivar = ivars[i];
            const char *ivarName = ivar_getName(ivar);
            NSString *ivarNameString = [NSString stringWithCString:ivarName encoding:NSASCIIStringEncoding];
            // You now have the name of the ivar as an NSString. You can compare it against whatever and decide what you want to do with it from here.
        }
    }

Thanks!

 

[ArtOfWarfare]

Thanks!

I would like to mention this is very low level stuff. I use code like this to find private classes/methods/properties in Cocoa/Cocoa Touch. If you're using it in actual production code, it would indicate your code was very poorly engineered.

IE, just the other day I used this to find the private method _setCollapsed:forView: on Apple's NSSplitView, so that I could call that method within my own code.