Getting an Objective-C class name without having a MonoTouch managed class

c#, ios, objective-c, translate, xamarin.ios

Solution

In general, @Monoman's `is` solution is the right way to find instances of a particular class, even when you're looking for a CocoaTouch class from within a MonoTouch program.

Sometimes, however, you'll discover that there's an internal CocoaTouch class that's not exposed in MonoTouch (or even in the iOS Platform headers). In such a case, you'll have to resort to tricks like @poupou is doing.

Unfortunately, his answers won't work here either. `view.GetType()` is returning the most-derived MonoTouch type that each `Subview` implements, and then `ToString()`, `Class.Name`, or even `@selector("description")` each operate on the wrong type and give an overly generic answer ("`UIView`" in this case).

In order to make this work, you'll have to go one layer deeper under the covers than @poupou proposed.

// ** using MonoTouch.ObjCRuntime; **

private string GetClassName (IntPtr obj) {
    Selector description = new Selector ("description");
    Selector cls = new Selector ("class");
    IntPtr viewcls = Messaging.IntPtr_objc_msgSend (obj, cls.Handle);
    var name = NSString.FromHandle (Messaging.IntPtr_objc_msgSend (viewcls, description.Handle));
    return name;
}

Here's an alternative that's not a whole lot more fiddly (maybe even less?), but will work on any Objective-C class, not just those that respond to `NSObject`'s `description` message:

// ** using System.Runtime.InteropServices; **

[DllImport ("/usr/lib/libobjc.dylib")]
private static extern IntPtr object_getClassName (IntPtr obj);

private string GetClassName (IntPtr obj) {
    return Marshal.PtrToStringAuto(object_getClassName(obj));
}

It's actually surprising and a little bit sad that MonoTouch doesn't provide an import for `object_getClassName()` already.

You would use either one of those like so:

foreach (UIView view in cell.Subviews) {
    if (GetClassName(view.Handle) == "UITableViewCellReorderControl") {
    }
}

Big fat disclaimer: Pretty much any time you're resorting to tricks like these, you're relying on CocoaTouch implementation details that Apple reserves the right to change. Rule of thumb: if you can do what you want with @Monoman's solution, you're probably safe. Otherwise, you're taking matters in to your own hands.

Problem

Original source