abock/JSExport.cs Secret

## JSExport.cs
//
// ViewController.cs
//
// Author:
//   Aaron Bockover <abock@xamarin.com>
//
// Copyright 2015 Xamarin Inc. All rights reserved.

using System;

using Foundation;
using JavaScriptCore;
using AppKit;
using WebKit;

namespace JSExportTest
{
	public partial class ViewController : NSViewController
	{
		public ViewController (IntPtr handle) : base (handle)
		{
		}

		public override void ViewDidLoad ()
		{
			base.ViewDidLoad ();

			// ideally we would subscribe to webView.JavaScriptContextCreated, but
			// XM does not bind WebKit/JSC-ObjC bridge APIs:
			// https://bugzilla.xamarin.com/show_bug.cgi?id=32975
			webView.FinishedLoad += (sender, e) => {
				var doc = webView.MainFrameDocument;
				AttachListener (doc.GetElementById ("broken-button"), new BrokenDomEventListener ());
				AttachListener (doc.GetElementById ("working-button"), new DomEventListener ());
			};

			webView.MainFrame.LoadHtmlString (
				@"<html><body>
				<button id='broken-button'>Broken</button>
				<button id='working-button'>Working</button>
				</body></html>",
				null);
		}

		void AttachListener (DomElement elem, NSObject listener)
		{
			// should just be webView.MainFrame.JavaScriptContext (bug #32975)
			var jsContext = JSContext.FromJSGlobalContextRef (webView.MainFrame.GlobalContext);
			// should just be elem.JSValue (bug #32975)
			var jsButton = JSValue.FromJSJSValueRef (elem.JSObject, jsContext);

			jsButton.Invoke ("addEventListener",
				JSValue.From ("click", jsContext), // event
				JSValue.From (listener, jsContext), // listener
				JSValue.From (true, jsContext) // useCapture
			);
		}

		// The broken event listener's HandleEvent(JSValue) will not be invoked
		// as it appears the XM runtime is blocking trying to convert the JSC
		// value to a JSValue (or any NSObject...)
		[Protocol]
		interface IBrokenDomEventListener : IJSExport
		{
			[Export ("handleEvent:")]
			void HandleEvent (JSValue evnt);
		}

		class BrokenDomEventListener : NSObject, IBrokenDomEventListener
		{
			public void HandleEvent (JSValue evnt)
			{
				Console.WriteLine ("JS -> C# Event: {0}", evnt);
			}
		}

		// Luckily a workaround is to export a method to JSC with no arguments
		// and access the current invocation's arguments via JSContext
		[Protocol]
		interface IDomEventListener : IJSExport
		{
			[Export ("handleEvent")]
			void HandleEvent ();
		}

		class DomEventListener : NSObject, IDomEventListener
		{
			public void HandleEvent ()
			{
				Console.WriteLine ("JS -> C# Event: {0}", JSContext.CurrentArguments [0]);
			}
		}
	}
}
	//
	// ViewController.cs
	//
	// Author:
	// Aaron Bockover <abock@xamarin.com>
	//
	// Copyright 2015 Xamarin Inc. All rights reserved.

	using System;

	using Foundation;
	using JavaScriptCore;
	using AppKit;
	using WebKit;

	namespace JSExportTest
	{
	public partial class ViewController : NSViewController
	{
	public ViewController (IntPtr handle) : base (handle)
	{
	}

	public override void ViewDidLoad ()
	{
	base.ViewDidLoad ();

	// ideally we would subscribe to webView.JavaScriptContextCreated, but
	// XM does not bind WebKit/JSC-ObjC bridge APIs:
	// https://bugzilla.xamarin.com/show_bug.cgi?id=32975
	webView.FinishedLoad += (sender, e) => {
	var doc = webView.MainFrameDocument;
	AttachListener (doc.GetElementById ("broken-button"), new BrokenDomEventListener ());
	AttachListener (doc.GetElementById ("working-button"), new DomEventListener ());
	};

	webView.MainFrame.LoadHtmlString (
	@"<html><body>
	<button id='broken-button'>Broken</button>
	<button id='working-button'>Working</button>
	</body></html>",
	null);
	}

	void AttachListener (DomElement elem, NSObject listener)
	{
	// should just be webView.MainFrame.JavaScriptContext (bug #32975)
	var jsContext = JSContext.FromJSGlobalContextRef (webView.MainFrame.GlobalContext);
	// should just be elem.JSValue (bug #32975)
	var jsButton = JSValue.FromJSJSValueRef (elem.JSObject, jsContext);

	jsButton.Invoke ("addEventListener",
	JSValue.From ("click", jsContext), // event
	JSValue.From (listener, jsContext), // listener
	JSValue.From (true, jsContext) // useCapture
	);
	}

	// The broken event listener's HandleEvent(JSValue) will not be invoked
	// as it appears the XM runtime is blocking trying to convert the JSC
	// value to a JSValue (or any NSObject...)
	[Protocol]
	interface IBrokenDomEventListener : IJSExport
	{
	[Export ("handleEvent:")]
	void HandleEvent (JSValue evnt);
	}

	class BrokenDomEventListener : NSObject, IBrokenDomEventListener
	{
	public void HandleEvent (JSValue evnt)
	{
	Console.WriteLine ("JS -> C# Event: {0}", evnt);
	}
	}

	// Luckily a workaround is to export a method to JSC with no arguments
	// and access the current invocation's arguments via JSContext
	[Protocol]
	interface IDomEventListener : IJSExport
	{
	[Export ("handleEvent")]
	void HandleEvent ();
	}

	class DomEventListener : NSObject, IDomEventListener
	{
	public void HandleEvent ()
	{
	Console.WriteLine ("JS -> C# Event: {0}", JSContext.CurrentArguments [0]);
	}
	}
	}
	}