How to ignore user clicks in WinForms? - winforms

Question

When a user clicks a button, it starts some task. I don't want to block the main application thread, so I run it in a separate thread. Now I need to forbid a user to click the button until my task finishes.
I could set
button.Enabled = false;
, but I'm looking for some way to ignore clicks on it.
I could add some check in click event handler:
if (executingThread != null) return;
, but I will have to do it for each handler which is bad idea.
I know that there is some way to filter user's messages. Could you point me how to do this? And I don't want to filter out all messages, because some other buttons must stay clickable, I need to filter out messages that come to particular controls (buttons,grids and etc).
SOLUTION
internal class MessagesFilter: IMessageFilter
{
private readonly IntPtr ControlHandler;
private const int WM_KEYUP = 0x0101;
public MessagesFilter(IntPtr ControlHandler)
{
this.ControlHandler = ControlHandler;
}
#region IMessageFilter Members
public bool PreFilterMessage(ref Message m)
{
// TODO: Add MessagesFilter.PreFilterMessage implementation
if (m.Msg == WM_KEYUP)
{
if (m.HWnd == ControlHandler)
{
Keys k = ((Keys) ((int) m.WParam));
if (k == Keys.Enter)
return true;
}
}
return false;
}
#endregion
}

Answer 1

As always, the UI should be presented in such a way that user understands what the application is doing and should talk to the user with UI elements.
As Adam Houldsworth suggested I would also prefer keeping the button either disabled or enabled but I would also suggest that the caption of the button should convey the message to the user that the long processing is in progress when the new thread starts..and so the caption of the button should be immediately changed to something like "Processing..Please wait..." (in addition to being disabled or even if you want to keep it enabled), and then if you have kept the button enabled just check the caption of the button (or a isProcessing bool flag) on its click event to return if it says "Processing..Please wait..." or (isProcessing == true).
Lots of the Websites which help users to upload files/images change the Upload button's caption to "Uploading..Please wait..." to inform the user to wait until the upload finishes and additionally some sites also disable the upload button so that the user is not able to click again on Upload button.
You would need to also revert back the caption to normal when the thread finishes long processing.
There may be other advanced ways but the idea is to keep it as simple and basic as possible.
Look at this example on Threading in Windows Forms which shows to disable the button while multi-threading.

Answer 2

+1 for all the suggestions so far. As CSharpVJ suggests - My idea was to additionally inform the user by changing the button's caption making the UI design more intuitive
This can be achieved elegantly with Backgroundworker component in Winforms [No hassles code]. Just copy-paste and HIT F5 (After creating a New Winforms Project with a Button and a Label on it)!
You do not have to check anything related to button here. Everything will be taken care by the appropriate event handlers. its just that you have to do correct stuffs int he resepctive event handlers. Try it !
using System.ComponentModel;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form3 : Form
{
private BackgroundWorker _worker;
public Form3()
{
InitializeComponent();
InitWorker();
}
private void InitWorker()
{
if (_worker != null)
{
_worker.Dispose();
}
_worker = new BackgroundWorker
{
WorkerReportsProgress = true,
WorkerSupportsCancellation = true
};
_worker.DoWork += DoWork;
_worker.RunWorkerCompleted += RunWorkerCompleted;
_worker.ProgressChanged += ProgressChanged;
}
/// do time consuming work here...
void DoWork(object sender, DoWorkEventArgs e)
{
int highestPercentageReached = 0;
if (_worker.CancellationPending)
{
e.Cancel = true;
}
else
{
double i = 0.0d;
for (i = 0; i <= 199990000; i++)
{
// Report progress as a percentage of the total task.
var percentComplete = (int)(i / 199990000 * 100);
if (percentComplete > highestPercentageReached)
{
highestPercentageReached = percentComplete;
// Report UI abt the progress
_worker.ReportProgress(percentComplete);
_worker.CancelAsync();
}
}
}
}
void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
button1.Enabled = true;
if (e.Cancelled)
{
// Display some message to the user that task has been
// cancelled
label1.Text = "Cancelled the operation";
}
else if (e.Error != null)
{
// Do something with the error
}
button1.Text = "Start again";
}
void ProgressChanged(object sender, ProgressChangedEventArgs e)
{
label1.Text = string.Format("Result {0}: Percent {1}",e.UserState, e.ProgressPercentage);
}
private void OnStartClick(object sender, System.EventArgs e)
{
_worker.RunWorkerAsync();
button1.Text = "Processing started...";
button1.Enabled = false;
}
}
}

Answer 3

As mentioned in other answers, there is probably a better solution than what you are asking for.
To directly answer your question, check out the IMessageFilter interface
Create your filter to have it suppress the mouse messages you don't desire, apply it when necessary using Application.AddMessageFilter().
Something along these lines (this should probably compile...):
public class MouseButtonFilter : IMessageFilter
{
private const int WM_LBUTTONDOWN = 0x0201;
private const int WM_LBUTTONUP = 0x0202;
private const int WM_LBUTTONDBLCLK = 0x0203;
private const int WM_RBUTTONDOWN = 0x0204;
private const int WM_RBUTTONUP = 0x0205;
private const int WM_RBUTTONDBLCLK = 0x0206;
private const int WM_MBUTTONDOWN = 0x0207;
private const int WM_MBUTTONUP = 0x0208;
bool IMessageFilter.PreFilterMessage(ref Message m)
{
switch (m.Msg)
{
case WM_LBUTTONDOWN:
/* case ... (list them all here; i'm being lazy) */
case WM_MBUTTONUP:
return true;
}
return false;
}
}