Solved

How to update a dropdown when a text field is updated automatically

Posted on 2008-10-31
4
159 Views
Last Modified: 2013-12-17
I have a file selector that when a file is selected a text box is populated.  When that text box is updated through code I need a dropdown populated.  My question is how can I get the code to know when a text field is updated?  I have tried TextBox1_TextChanged but that only triggers if I manually update the text field.
0
Comment
Question by:tmctogo
  • 3
4 Comments
 
LVL 13

Expert Comment

by:numberkruncher
ID: 22851696
You can set the "AutoPostBack" property of the text box control to "True" and it will automatically generate a post back when the text is changed.

If you need a custom JavaScript postback, then you get an event reference via the Page.ClientScript object.
0
 

Author Comment

by:tmctogo
ID: 22851728
I already have AutoPostBack set to true.  The only time that the process for populating the dropdown is started is when I change the text in the field manually.  Since I am using a fileupload control, it does not have postbacks so I populate a text box with the value from the fileupload control.
0
 
LVL 13

Expert Comment

by:numberkruncher
ID: 22851749
Okay, so it sounds like you need a custom post back. Give me a few minutes and I will post you an example which allows you to do this.
0
 
LVL 13

Accepted Solution

by:
numberkruncher earned 125 total points
ID: 22851910
First an explanation of how the code below works:

A custom post back event has been registered via the ClientScript object. The post back is registered for the page itself. But in-order to be able to respond to this post back you must implement the 'IPostBackEventHandler' interface. Your special server-side post back code goes in the method provided there.

In the example I have demonstrated how to access the text box value.
In the HTML section of the website:
 
    <script type="text/javascript">
        function myTestFunction() {
            // Simply call the following function to do postback.
            firePostback('MyTextChanged');
        }
    </script>
 
I used the following to test this:
 
    <input type="button" value="Test" onclick="myTestFunction()" />
 
In your code file:
 
 
public partial class Default5 : System.Web.UI.Page, IPostBackEventHandler
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // Register the event reference.
        // "@XXX@" gets replaced with the name attribute of firePostback.
        //      i.e. firePosback('boo')   replaces "@XXX@" with "boo".
        string customEventReference = ClientScript.GetPostBackEventReference(this, "@XXX@");
        // Register the post back function.
        ClientScript.RegisterClientScriptBlock(GetType(), "DoTextChanged",
            string.Format("function firePostback(name) {{ eval(\"{0}\".replace('@XXX@', name)); }}", customEventReference), true);
    }
 
 
    #region IPostBackEventHandler Members
 
    public void RaisePostBackEvent(string eventArgument)
    {
        // Check for the argument which was provided to our post back function.
        if (eventArgument == "MyTextChanged")
        {
            string textBoxValue = TextBox1.Text;
        }
    }
 
    #endregion
}

Open in new window

0

Featured Post

On Demand Webinar - Networking for the Cloud Era

This webinar discusses:
-Common barriers companies experience when moving to the cloud
-How SD-WAN changes the way we look at networks
-Best practices customers should employ moving forward with cloud migration
-What happens behind the scenes of SteelConnect’s one-click button

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Because your company can’t afford for you to make SEO mistakes, you’ll want to ensure you’re taking the right steps each and every time you post a new piece of content. This list of optimization do’s and don’ts can help you become an SEO wizard.
There’s a good reason for why it’s called a homepage – it closely resembles that of a physical house and the only real difference is that it’s online. Your website’s homepage is where people come to visit you. It’s the family room of your website wh…
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…
The is a quite short video tutorial. In this video, I'm going to show you how to create self-host WordPress blog with free hosting service.

685 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question