Passing js callbacks into winRT cpp application

Question

Hi,

does anyone know whether it is possible to pass js function into C++ code via delegates and then invoke it:

nearly like this:

// js: 
var f = function () { }

nativeObject.setDelegate(f);

// cpp

public delegate void SimpleDelegate();

void WinRTComponent::setDelegate(SimpleDelegate^ del)
{

del->invoke();

}

may be there any other methods to do such things?

thanks in advance,

Nick

Answer 1

Hello,

I tested this codes and works on my side.

// C++ codes
// In head file
namespace namespacedll
{
	public delegate int add( int a, int b);
    public ref class winRTComponent sealed
    {
		
    public:
        winRTComponent();
		void calldelegate(add^ func);
    };
}

// In CPP files
winRTComponent::winRTComponent()
{
}
void winRTComponent::calldelegate(add^ func)
{
	int res=func(3,4);
}

// In Javascript files
var foo =  function (a, b) { return a + b };

var component =new namespacedll.winRTComponent();
component.calldelegate(foo);

For more information. Please check the Delegates and events section in this document

http://msdn.microsoft.com/en-us/library/windows/apps/hh441569(v=vs.110).aspx

Best regards,
Jesse

---

Jesse Jiang [MSFT]
MSDN Community Support | Feedback to us

Answer 2

Hi Jesse,
thanks for you advice,

i see now that the problem was in the "->invoke()" delegate calling.

thanks,
  Nick

Answer 3

Hi Jessie,

How can the same be achieved in a C# RT Component,

Can you explain with sample, I have tried but I am stuck with an error that the line where I do the function call from C# (referring to the callback function passed on from Javascript. My code in Javascript is like this,

My.WinRT.Component.Object.processEachRowASyc(query, arguments, function(row) {
    /* Row specific processing */
}).then(function(result) {
    /* Process after Entire Row processing is Complete */
});

And the code in the C# Runtime Component is like this,

namespace mydb
{
    public void delegate MyJSCallback(string msg);
    public class Database {

        public static IAsyncOperation<Database> OpenDB(string dbFile)
        {
           /* Open DB */
        }

        public IAsyncOperation<Database> ProcessEachRowASync(string sql,[ReadOnlyArray()] object[] arg, MyJSCallback myJSCallback)
        {
            return Task<IDataReader>.Run(() =>
            {
            /* Query Processing */
            IDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
               RowObject toRet = reader.GetMyRowObject();
               myJSCallback(toRet);
            }
            return this;

            }).AsAsyncOperation();
        }
    }

}

Believe I am missing something, if you could guide me in the right direction, I will be grateful,

Thanks in advance for your help,

Best Regards,

Jay

Answer 4

When I removed the IASyncOperation from the function, the js callback worked without issue.

There seems to be a problem because I am having a blocking callback function sent as the parameter I believe. Can any one clarify how it can work with IASyncOperation present in my function.

Regards,

Jay

Answer 5

when you want to call a JS function from an async context you need the main thread dispatcher for the apps window. You then use the dispatcher to call your JS method:


save the dispatcher before you create the Task:
CoreDispatcher^ dispatcher = CoreWindow::GetForCurrentThread()->Dispatcher;

Inside the task:

dispatcher->RunAsync(CoreDispatcherPriority::Normal, handler);

where handler is a DispatchedHandler