How to add a category to a “hidden” class

Question

Is there a way to add a category to a class whose header file you can't access?

For testing purposes, I want to add a category to UITableViewCellDeleteConfirmationControl, but the class is (as far as I can tell) part of a private framework.

How can I do that?

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Elaboration (per mihirios's request):

I am trying to extend the Frank testing framework to simulate tapping the confirmation button (the big red "Delete" button) that appears when you try to delete a UITableViewCell. Frank adds a tap method to UIControl. For some reason, Frank's usual way of tapping a control does not work for the UITableViewCellDeleteConfirmationControl class (which subclasses UIControl).

I've create a workaround. I added a category to UITableViewCell, with the following method.

- (BOOL)confirmDeletion {
    if (![self showingDeleteConfirmation]) {
        return NO;
    }
    UITableView *tableView = (UITableView *)[self superview];
    id <UITableViewDataSource> dataSource = [tableView dataSource];
    NSIndexPath *indexPath = [tableView indexPathForCell:self];
    [dataSource tableView:tableView
       commitEditingStyle:UITableViewCellEditingStyleDelete
        forRowAtIndexPath:indexPath];
    return YES;
}

This finds the table's data source and invokes its tableView:commitEditingStyle:forRowAtIndexPath: method, which (according to the documentation for UITableView) is what the system does when the user taps the confirmation button.

This works, but I would prefer to make UITableViewCellDeleteConfirmationControl appear to be a tappable button by adding a tap method to it, overriding Frank's default one. The tap method would find the cell that contains the confirmation button, then invoke [cell confirmDeletion].

When I try to declare a category for UITableViewCellDeleteConfirmationControl, the compiler complains that it "can't resolve interface 'UITableViewCellDeleteConfirmationControl'."

When I try to use the header file that someone generated using class-dump, the linker complains that it can't find the symbol _OBJC_CLASS_$_UITableViewCellDeleteConfirmationControl.

Answer 1

For testing purposes, you can always get the class object using NSClassFromString and then use the class_replaceMethod runtime method to do whatever you need. See the Objective-C Runtime Reference for details.

Answer 2

As far as i know you can not use a Category, but you could add the methods manually during runtime.

A Possible way to do this is, to create a new class, implement the methods you want to, and send this methods to UITableViewCellDeleteConfirmationControl using the appropriate objc-runtime functions. There are some things to take care of, like storing the original functions for later use in case of overloading, also in your 'category'-class you have to pay attention when you want to call super, as this will not work, you have to use objc-runtime function objc_msgSendSuper instead.

As Long as you don't need to call super this will do fine:

#import <objc/runtime.h>
#import <objc/message.h>

void implementInstanceMethods(Class src, Class dest) {
    unsigned int count;
    Method *methods = class_copyMethodList(src, &count);

    for (int i = 0; i < count; ++i) {
        IMP imp = method_getImplementation(methods[i]);
        SEL selector = method_getName(methods[i]);
        NSString *selectorName = NSStringFromSelector(selector);
        const char *types = method_getTypeEncoding(methods[i]);

    class_replaceMethod(dest, selector, imp, types);        
    }
    free(methods);
}

a good point to call the method is in main.m, for example:

@autoreleasepool {
        implementInstanceMethods([MyCategory class], NSClassFromString(@"UITableViewCellDeleteConfirmationControl"));
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([YourAppDelegate class]));
}

But i don't know why you not just move the confirmation handling in the controller-class.

Answer 3

As long as the compiler can (eventually) link to the class in question you can create a category for it. The more important question will be how to design the category since it seems you do not have access to the source for the original class.