Asp.Net button has no ID in javascript?

Question

I have some problems identifying an asp.net control in javascript. Here's a simple variant of my code, maybe you can see an error.

This function creates a set of button + label, it can be called multiple times:

    private void AddRow(Panel pnl)
    {
        var myButton = new Button();
        myButton.Text = "+";
        myButton.Attributes.Add("onclick", "return MyJavascript();");
        myButton.Attributes.Add("somevariable", "FOOBAR!");

        var lblAnzahl = new Label();

        pnl.Controls.Add(myButton);
        pnl.Controls.Add(lblAnzahl);
    }

This is the JS function the button calls:

            function MyJavascript(e) {
                var sender = event.target || event.srcElement;
                var somevar = sender.getAttribute("somevariable");
                alert('somevar: ' + somevar);
                alert('ID: ' + sender.id);
            }

The output is:

somevar: FOOBAR!

ID:

So I guess I get the correct sender, but for some reason the ID is always empty. The easiest way for me would be, if I could somehow set the ID of button and label myself, so that I can give it an unique ID every time AddRow() gets called, so I can easily identify the button and of course the label that belongs to the button.

What am I doing wrong?

Need to create the client ID in a predictable way. MSDN Video — juanvan
– juanvan, Commented Apr 14, 2014 at 13:08
Check clientid spelled correctly :) msdn.microsoft.com/de-de/library/… — Rand Random
– Rand Random, Commented Apr 14, 2014 at 13:12

User.Anonymous · Accepted Answer · 2014-04-14 13:07:45Z

2

You can use myButton.ClientID or add name attribute myButton.Attributes.Add("name", "FOOBAR"); with check to be sure that name is unique and retrieve in Javascript by getElementByName

answered Apr 14, 2014 at 13:07

User.Anonymous

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1 Comment

Core_F Over a year ago

myButton.ClientID is readyonly and doesn't return anything either. I've also tried var mybutton = document.getElementsByName("FOOBAR")[0], but then mybutton is undefined.

bastos.sergio · Accepted Answer · 2014-04-14 13:15:11Z

1

You're not setting an ID in your AddRow function.

Change your function to this:

private void AddRow(Panel pnl, int index)
{
    var myButton = new Button();
    myButton.ID = "button_" + index; // add this line (the index will guarantee a distinct ID)
    myButton.Text = "+";
    myButton.Attributes.Add("onclick", "return MyJavascript();");
    myButton.Attributes.Add("somevariable", "FOOBAR!");

    var lblAnzahl = new Label();

    pnl.Controls.Add(myButton);
    pnl.Controls.Add(lblAnzahl);
}

You can invoke the code like this:

AddRow(pnl, 0);
AddRow(pnl, 1);
AddRow(pnl, 2);

edited Apr 14, 2014 at 13:15

answered Apr 14, 2014 at 13:10

bastos.sergio

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2 Comments

Core_F Over a year ago

Ah, ok... ID in asp.net = ClientID in javascript. Thanks, that helped. :)

bastos.sergio Over a year ago

Hum, not quite... Javascript, as a standalone language, does not know about ClientID's. The ClientID terminology is only used in asp.net. The thing is, in asp.net you can't set the ClientID to a control, you have to set the ID value instead. This in turn will make the asp.net framework generate a proper ClientID, which you can then reference from javascript.

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