How to change a GUI control state by the event handler

Question

Request description

I'm handling a project which need to call a background process to read some data from database. The get data button of the GUI will turn to gray during this time and turn to enable after the data arrived. If there is any exception throw from the background process the button need to turn to enable to make sure the user could send another request.

Problem description

One get data failed event is added to the background process to let the UI thread notice there is a exception encountered by the get data process. But the state of the button can't be changed in the event handler function due to there are running in the difference thread.

Relative codes snippets

Back ground thread code

class DataProcessService
{
    public static SingletonInstance {get;set;} //Omit the codes implement the singleton pattern
    public event EventHandler GetDataFailed;

    private void FireGetDataFailed()
    {
       if(GetDataFailed != null) GetDataFailed(this, null);
    }

    // in some function 
    try
    {
        // do some get data process
    }
    catch(SqlException ex)
    {
       FireGetDataFailed();
    }

}

GUI codes

//In the init function subscribe to the event
DataProcessService.SingletonInstance.GetDataFailed += new Eventhandler(GetDataFailedEventHander_EnableButtonState);

private void GetDataFailedEventHander_EnableButtonState(object s, EventArgs e)
{
    btnGet.Enabled = true;  //There will be a exception
}

Questions

How to change the UI control from the event hander in .net 3.5? In .net 4.0 may be I could use TPL to handle this. Any suggestions will be appreciated, thanks.

Development environment

VS2008, .net 3.5

I assume this is winforms?, since most winforms developers don't even bother to add the proper tags because they actually have no idea that other (much better) UI technologies exist within the .Net stack. — Federico Berasategui, Feb 01 '13 at 03:12
[Possible Duplicate question](http://stackoverflow.com/questions/709187/accessing-ui-in-a-thread) — Federico Berasategui, Feb 01 '13 at 03:16

score 2 · Answer 1 · answered Feb 01 '13 at 03:18

2

You will have to invoke it back onto the UI thread

private void GetDataFailedEventHander_EnableButtonState(object s, EventArgs e)
{
    base.Invoke((Action)delegate { btnGet.Enabled = true; }); 
}

answered Feb 01 '13 at 03:18

sa_ddam213

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Can I use a lambda expression by the Invoke method? – Erxin Feb 01 '13 at 03:26
Don't think so the parameter is `System.Delegate` which is not a delegate type (despite the name) :) – sa_ddam213 Feb 01 '13 at 03:37