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.