xsharp.eu

Posted: **Tue Sep 27, 2022 9:21 pm**

This C# code:

	public static void ProcessUITasks()
	// When called, forces the UI to redraw. 
	{
		DispatcherFrame frame = new DispatcherFrame();
		Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background, new DispatcherOperationCallback(delegate (object parameter) {
			frame.Continue = false;
			return null;
		}), null);
		Dispatcher.PushFrame(frame);
	}

in ILSpy translates as:

Code: Select all

public static method ProcessUITasks() as void
	local frame as DispatcherFrame
	frame := DispatcherFrame{}
	Dispatcher.CurrentDispatcher:BeginInvoke(DispatcherPriority.Background, (DispatcherOperationCallback){ =>
		frame:Continue := false
		return null
	}, null)
	Dispatcher.PushFrame(frame)

This gives Error XS1593 Delegate 'System.Windows.Threading.DispatcherOperationCallback' does not take 0 arguments

Indeed delegate (object parameter) from the C# code is missing. But I am not sure how to do this in X#

Anyone an idea?

Dick

Posted: **Wed Sep 28, 2022 5:54 am**

Hi Dick,

This should do it, by supplying the parameter as the c# version of the code does:

Code: Select all

	Dispatcher.CurrentDispatcher:BeginInvoke(DispatcherPriority.Background, (DispatcherOperationCallback){ parameter AS OBJECT =>
		frame:Continue := FALSE
		RETURN NULL
	}, NULL)

Posted: **Wed Sep 28, 2022 6:54 pm**

Hello Chris,

Thanks, it works now.

I must confess that I have no idea how the syntax is supposed to work; any Lambda expressions or "delegates" in my program are "borrowed" and even now I see your working X# solution I do not understand how you got to this (gone is the delegate, added is the =>).

But main thing is that it works!

Dick

Posted: **Wed Sep 28, 2022 8:42 pm**

Dick,

There are 2 ways to write this:
- A Lambda expression (with the => operator, like you did)
- With the DELEGATE keyword

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Dispatcher.CurrentDispatcher:BeginInvoke(DispatcherPriority.Background, (DispatcherOperationCallback){ DELEGATE ( p AS OBJECT )  {  frame:Continue := FALSE, NULL }, NULL)

The syntax for the DELEGATE expression is

Code: Select all

DELEGATE [ ( Parameters) ] { <Block> }

Where <Block> is :
- a single expression
- an expression list, seperated with commas. The last expression is the return value, like above. All on one line.
- a statement block (starts with a CRLF after the LCurly ({) and also has a CRLF before the RCurly (})

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