Javascript : call a C# function

Question

firstly i have searched a lot and all topics seems to be C# : call or invoke a JavaScript function but i want to do the opposite , i want to create a function on C# and also on JavaScript and i want the JavaScript function call the C# function and retrieve it`s data , it seems like a good questions . The problem is that i have no knowledge on web and i do not know how does it work , but i tried a sample :

Created a class :

public interface IFoo
{
    string Bar { get; set; }
}

public class Foo : IFoo
{
    public string Bar { get; set; }
}

Then

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }

    public IFoo CreateFoo()
    {
        return new Foo() { Bar = "somevalue" };
    }

    public string Bar(IFoo foo)
    {
        return foo.Bar;
    }
}

And Javascript Code :

<script type="text/javascript" language="javascript" >

function Callme(){
alert('Js function start . keep pressing OK')
var foo = external.CreateFoo();
alert(foo.Bar);
foo.Bar = "qwer";
alert(external.Bar(foo));
}
</script>

I get Error from the webbrowser control :

Error : "external" is null or not an object

But the javascript is not showing anything , please guide me if i missed something.

+1 to this question to offset -1 : I do not think that the question should get downvote only because the OP does not know about how particular technology/protocol/framework works. — Michael
– Michael, Commented Mar 27, 2012 at 9:15
I downvoted not for his ignorance, but for his ambiguous question. — Kevin Wang
– Kevin Wang, Commented Mar 27, 2012 at 9:18

Kevin Wang · Accepted Answer · 2012-03-27 11:56:52Z

7

Hold on guys. PAUSE. All of you need to slow down and read. As this guy said:

 I get Error from the webbrowser control :

Meaning he is embedding a webbrowser control that opens up this page which runs javascript.

To clear this up, I think he means that:

This is not online.
He has a webBrowserControl in his C# application that opens up a page to run this javascript.
In his app, he wants to use javascript to call a C# method from a class in his app.

Now, I agree that he was a bit ambiguous (hint, please be clearer with your question next time), but you guys are all posting answers and getting ahead of yourself. In fact what he is describing is indeed possible, and this is how you do it.

Now the object you wanna reference in your javascript is window.external. Here is an example in your javascript:

window.external.CreateFoo();

to call CreateFoo(). However, before you can do so, you have to make your class visible to the page that your webbrowser is opening (window.external being the instanced class that you're referencing).

So, to set window.external, when you're creating webBrowser in C#:

webBrowser1.ObjectForScripting = this;

So to sum it up:

In your C# app, set ObjectForScripting of your web browser control to whatever object you want to reference in Javascript.
In the Javascript on your page, you can call window.external.YOURMETHOD(); to call any public method from that ObjectForScripting class that you set originally.

I hope this helps your situation and others will be a bit more careful when reading your question.

EDIT: Also as a reminder, the webBrowserControl depends on the version on IE that the user has installed on his/her computer. So be careful on versioning, javascript will only perform to the extent of what his/her version of IE can handle (same goes for styling and etc.)

Edit Edit: You also need to add the ComVisible attribute [ComVisible(true)]

edited Mar 27, 2012 at 11:56

answered Mar 27, 2012 at 9:17

Kevin Wang

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4 Comments

R.Vector Over a year ago

that you so much for your answer and understanding , but when i applied your solution on my form i set webBrowser1.ObjectForScripting = this; But i get error : System.ArgumentException: ObjectForScripting's class must be visible to COM. Verify that the object is public, or consider adding the ComVisible attribute to your class. at System.Windows.Forms.WebBrowser.set_ObjectForScripting(Object value)

R.Vector Over a year ago

Okay no problem i have fixed that by adding : using System.Runtime.InteropServices; [ComVisible(true)] above the public interface

Kevin Wang Over a year ago

^yes I forgot to add that you need the ComVisible attribute

Jerome Cance Over a year ago

+1 thanks for explanation. That was quite ambigous. Thanks to clarifying that and for answering correctly ;)

Jerome Cance · Accepted Answer · 2012-03-27 09:06:58Z

1

there is some misunderstood here.

Javascript can't call server function.

Use Ajax for that.

The only way we can think about that is in a framework like GWT, but be careful : GWT compile your java code in javascript which calls via ajax the server.

The thing to have in memory is that if a framework propose you to call a C# or java method directly in javascript, it does not really perform that : it calls a server resource using ajax and then the server resource call the method. The method returns and the ajax response is sent to javascript.

answered Mar 27, 2012 at 9:06

Jerome Cance

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2 Comments

Kevin Wang Over a year ago

Jerome, I don't think he means that this is an online app. Instead, he is embedding the page in his offline C# app.

Jerome Cance Over a year ago

yes, I've seen your answer. Thank you to point us in the right direction ;)

Tigraine · Accepted Answer · 2012-03-27 09:07:39Z

1

You should really look into how HTTP works and then re-evaluate your question.

You simply can't call a C# function directly from JavaScript because your JavaScript is executed on the client by the browser while the C# is run on the server by the Web server.

If you want to call a function on the server you need to do that through a AJAX request using some kind of Web library like ASP.NET WebAPI or ASP.NET MVC.

answered Mar 27, 2012 at 9:07

Tigraine

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Comments

Richard · Accepted Answer · 2012-03-27 09:14:33Z

1

To explain Jerome C's answer slightly further.

C# is a server-side language which is executed by a server request. Whereas JavaScript is client-side language, meaning it is handled by the browser. Both have their advantages, and both are commonly used for the same thing, such as validation. The server-side language is a secure way of ensuring something, or executing a command between a database for example. Whereas the client-side language (JavaScript), is more commonly used to improve the user experience but making things more interactive.

As people have suggested, there are ways to communicate between the two, but not "directly". The key word here is AJAX. Using an open source library such as jQuery http://jquery.com/ on the client-side, and then a custom handler (.ASHX file) on the server-side, you can make asynchronous requests between the client and the server.

On a slightly more advanced note; you can directly communicate between JavaScript and C# objects using a library such as SignalR https://github.com/SignalR/SignalR it's a tiny bit fiddly to setup, so I wouldn't recommend it for this instance, but it would definitely be something to consider in the future.

answered Mar 27, 2012 at 9:14

Richard

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1 Comment

R.Vector Over a year ago

Thank you so much for your brief answer.

shenhengbin · Accepted Answer · 2012-03-27 09:15:00Z

0

You can't call server function by Javascript directly.

If you need , you can use the __doPostBack("Button1","") instead.

Put your action in the Button1's event.

answered Mar 27, 2012 at 9:15

shenhengbin

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Comments

marc_s · Accepted Answer · 2017-04-20 12:35:22Z

Javascript and serverside languages cannot directly talk to each other.

The most common (I think) way to do this is using some sort of Ajax call a serverside Web Service:

This means you make a special call in javascript that will reach to a class method written in C#.

Before reading about and making Ajax calls, you should read up on HTTP protocol and how communication between web server and browsers is executed. I think the article in this link is a good place to start reading about HTTP.

You can read about WebServices Web Services related Wiki article, and about Ajax in Ajax wiki Article.

Also :

Ajax calls do not have to be written by hand, javascript frameworks like jQuery can be used. (in jQuery a function like jQuery.$ajax() is very usefull in making ajax calls )
There is an alternative way to do this - you can use a page method.

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