使用C＃，如何更新另一个类的列表框项？

Question

Hy,

In my project asp.net (c#), I am using threading to process some messages. I have a display page that contain a listbox with all the actions that are taken in processing the message. And a class where I am processing the message.

Default.aspx:

        protected void Page_Load(object sender, EventArgs e)
        {
            //starts the thread and call the method from Process.cs
        }

        public void SetListItem(string text)
        {
            myListBox.Items.Add(text);
            myListBox.DataBind();
        }

Process.cs

public class Process
{
  public Process()
  {
    Default defaultPage;
    defaultPage.SetListItem("==> Received message!");
  }
}

But the listbox do not show nothing. Does anyone has any ideea where I'm wrong? Thanks.

Jeff

Answer 1

Remove the databind

 myListBox.DataBind();

You don't need it since you are adding an item to the list collection. If you were setting the DataSource property, you would then have to use it. This is all depending on where in the life-cycle your update is firing as well. It could be that your update is being replaced by code somewhere else in the process as well.

In truth, I would take this out of being a separate thread. Since you need it to be updated before the page submits information to the browser, you either need to keep it in the same thread to make sure it completes, or you're going to need to have some sort of a check at the end of your page executing process to make sure it has finished. It is possible your thread is completing after the page has finished processing.

Answer 2

An asp.net page, such as Default generates html which is returned to the requesting browser. When this html has been generated and sent to the browser, there is no way you can add items on the server side to whatever is displayed in the browser.

So spawning threads that do some work is not necesarily a good idea for your current scenario.

Answer 3

Klaus is right. Once the page has been drawn it's just sitting there.

So, to do what you want to do, running Process in a seperate thread: Write your output message in Process to a data store, even if that's just appending to a text file. Then, set your page to automatically refresh every X time, and refill your listbox on load with the content of that datastore.

Later on, when everything's working, you could use Ajax to make just the listbox refresh, instead of the whole page.