How can I execute Javascript callback function from C# host application

Question

I\'m creating an application in C# that hosts custom web pages for most of the GUI. As the host, I\'d like to provide a javascript API so that the embedded web pages can ac

Answer 1

You can use Reflection for that:

[ComVisible(true)]
public class ScriptObject
{
    public void LongRunningProcess(string data, object callback)
    {
        string result = String.Empty;

        // do work, call the callback

        callback.GetType().InvokeMember(
            name: "[DispID=0]",
            invokeAttr: BindingFlags.Instance | BindingFlags.InvokeMethod,
            binder: null,
            target: callback,
            args: new Object[] { result });
    }
}

You could also try dynamic approach. It'd be more elegant if it works, but I haven't verified it:

[ComVisible(true)]
public class ScriptObject
{
    public void LongRunningProcess(string data, object callback)
    {
        string result = String.Empty;

        // do work, call the callback

        dynamic callbackFunc = callback;
        callbackFunc(result);
    }
}

[UPDATE] The dynamic method indeed works great, and probably is the easiest way of calling back JavaScript from C#, when you have a JavaScript function object. Both Reflection and dynamic allow to call an anonymous JavaScript function, as well. Example:

C#:

public void CallbackTest(object callback)
{
    dynamic callbackFunc = callback;
    callbackFunc("Hello!");
}

JavaScript:

window.external.CallbackTest(function(msg) { alert(msg) })

Answer 2

As @Frogmouth noted here already you can pass callback function name to the LongRunningProcedure:

function onComplete( result )
{
    alert( result );
}

function start()
{
    window.external.LongRunningProcess( 'data', 'onComplete' );
}

and when LongRunningProcedure completes use .InvokeScript as the following:

    public void LongRunningProcess(string data, string callbackFunctionName)
    {
        // do work, call the callback

        string codeStrig = string.Format("{0}('{1}')", callbackFunctionName, "{{ Your result value here}}");
        webBrowser1.Document.InvokeScript("eval", new [] { codeStrig});  
    }