Accessing ASP 2.0 control via javascript returning Null for all controls

Question

Scene : I have a ASP.Net 2.0 app that I need to add functionality to. I need to loop through a gridview's items and compare them to another gridview, If they exist in the other, I must pop up a confirm message to increment the qty. I couldnt find alot on ASP 2.0 so i decided to user a hidden asp field to store what i am processing and based on that registering a clientside script to change the hidden field value and then simulate a postback (I have tried _doPostBack()). So whats happening now is I am trying to access the asp button to simulate a click, but the javascript gets a Null instance everytime. Please advise. (For the testing, i try to alert the button instance, which returns null)

ClientScript.RegisterStartupScript(GetType(String), "ConfirmationScript", "if (confirm('This item already exists, Increment the qty?') == true) {alert(document.getElementById('<%=btnAddSpecificLine.ClientID%>'));}", True)

That string will literally be put on the page. By that point, there's nothing to evaluate the ASP code <%=btnAddSpecificLine.ClientID%>. I believe you'll have to concatenate that script string with btnAddSpecificLine.ClientID instead of trying to evaluate it with <%= %> — Ian
– Ian, Commented May 31, 2013 at 14:28
It seems to return the actual <%=btnAddSpecificLine.ClientID%> in this case, So it doesnt resolve the clientid of the server control as it should — Dean Martin
– Dean Martin, Commented May 31, 2013 at 14:31

Comfortably Numb · Accepted Answer · 2013-05-31 14:28:53Z

2

Try your test like this:

ClientScript.RegisterStartupScript(GetType(String), "ConfirmationScript", "if (confirm('This item already exists, Increment the qty?') == true) {alert(document.getElementById('" & btnAddSpecificLine.ClientID & "'));}", True)

Since you generate this code server-side - pass ClientID directly

answered May 31, 2013 at 14:28

Comfortably Numb

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3 Comments

Dean Martin Over a year ago

You are the man! Thank you, Amazing how one could miss the obvious like this at times.

Dean Martin Over a year ago

Very odd though as the clientid's stayed the exact same as specified in the html... would have thought that they would change since its server controls.

Comfortably Numb Over a year ago

It changes if your control is hosted inside of some kind of a container - then the id becomes a combined ID of container ID + Control ID. Otherwise it remains the same, but it is always a good idea to use Client ID

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