How do I send parameters using MonoTouch.ObjCRuntime.Selector and Perform Selector

Question

Here is an example I found, but they omitted actually sending the params.

this.PerformSelector(new MonoTouch.ObjCRuntime.Selector("_HandleSaveButtonTouchUpInside"),null,0.0f);

[Export("_HandleSaveButtonTouchUpInside")]
    void _HandleSaveButtonTouchUpInside()
    {
...
}

I would like to be able to do something like this:

this.PerformSelector(new MonoTouch.ObjCRuntime.Selector("_HandleSaveButtonTouchUpInside"),null,0.0f);

[Export("_HandleSaveButtonTouchUpInside")]
    void _HandleSaveButtonTouchUpInside(NSURL url, NSData data)
    {
...
}

How do I change the PerformSelector Call to send params to the method?

Answer 1

The MonoTouch docs indicate that method maps to the Obj-C selector performSelector:withObject:afterDelay, which only supports invoking a selector with a single argument.

The best way to handle this depends what you need to do. One typical way to handle this would be to put the arguments as properties/fields on a single NSObject, then the target would be modified to have a single argument, and pull the real arguments off that method. If you did this with a custom MonoTouch object, you'd have to watch out for the GC collecting the managed peer, if nothing in managed code kept a reference to it.

A better solution would depend on exactly how you're using it. For example, in your example, you could trivially call the C# method directly, e.g.

_HandleSaveButtonTouchUpInside (url, data);

If you need to dispatch via Obj-C for some reason, but don't need the delay, use MonoTouch.ObjCRuntime.Messaging, e.g.

MonoTouch.ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (
    target.Handle,
    MonoTouch.ObjCRuntime.Selector.GetHandle ("_HandleSaveButtonTouchUpInside"),
    arg0.Handle,
    arg1.Handle);

If you need the delay, you could use an NSTimer. MonoTouch has added special support for this to use an NSAction delegate, so you can use a C# lambda to capture arguments safely.

NSTimer.CreateScheduledTimer (someTimespan, () => _HandleSaveButtonTouchUpInside (url, data));

Answer 2

I could not find the binding for this call either. In the sample below I added my own overload for PerformSelector. Maybe one of the Xamarin Engineers can confirm this.

using System;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using MonoTouch.ObjCRuntime;
using System.Runtime.InteropServices;

namespace delete20120506
{
    [Register ("AppDelegate")]
    public partial class AppDelegate : UIApplicationDelegate
    {
        UIWindow window;

        public override bool FinishedLaunching (UIApplication app, NSDictionary options)
        {
            window = new UIWindow (UIScreen.MainScreen.Bounds);

            // 
            Target target = new Target ();
            NSUrl url = new NSUrl ("http://xamarin.com/");
            NSData nsData = NSData.FromString ("Hello");

            target.PerformSelector (new MonoTouch.ObjCRuntime.Selector 
                                  ("TestSelUrl:withData:"), url, nsData);

            window.MakeKeyAndVisible ();

            return true;
        }
    }

    [Register ("Target")]
    public class Target : NSObject
    {
        public Target () : base (NSObjectFlag.Empty) {}

        [Export("TestSelUrl:withData:")]
        void TestSelUrlWithData(NSUrl url, NSData nsData)
        {
            Console.WriteLine ("In TestSelUrlWithData");
            Console.WriteLine (url.ToString ());
            Console.WriteLine (nsData.ToString ());
            return;
        }

        [DllImport ("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSend")]
        public static extern void void_objc_msgSend_intptr_intptr_intptr (IntPtr receiver, IntPtr selector, IntPtr arg1, IntPtr arg2, IntPtr arg3);

        [DllImport ("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSendSuper")]
        public static extern void void_objc_msgSendSuper_intptr_intptr_intptr (IntPtr receiver, IntPtr selector, IntPtr arg1, IntPtr arg2, IntPtr arg3);


        public virtual void PerformSelector (MonoTouch.ObjCRuntime.Selector sel, 
                                              NSObject arg1, NSObject arg2)
        {
            if (this.IsDirectBinding)
            {
                void_objc_msgSend_intptr_intptr_intptr (this.Handle, 
                    Selector.GetHandle ("performSelector:withObject:withObject:"),
                    sel.Handle, arg1.Handle, arg2.Handle);
            }
            else
            {
                void_objc_msgSendSuper_intptr_intptr_intptr (this.SuperHandle,
                    Selector.GetHandle ("performSelector:withObject:withObject:"), sel.Handle, 
                    arg1.Handle, arg2.Handle);
            }
        }
    }
}