My mdi VB.Net application performs a long operation on some data. Ideally I should use a separate thread to prevent the dreaded “Not Responding” message.
My problem is if I use a separate thread users then have the ability to click on other controls in the application which can directly affect the operation my background thread is working on, creating an error.
Is there any way to prevent all the mdi windows, toolbars and other controls from receiving mouse clicks and keyboard input during my background thread’s operation?
Or is there a way to clear the message que before performing a Application.DoEvents?
Thanks
I would say that the best choice when you don't want a user to click on a control is to set Enabled to False for that control.
CLARIFICATION: Setting Enabled to False for a parent control will also disable any children. So, setting Enabled to False on the main window and and MDI windows, will do the trick.
There are a couple of ways of disabling the controls but I'm not sure it's what you want.
If you have a main window which is completely disabled while a background thread is processing then why go through the overhead of processing on the background? The advantage of processing on the background is to allow the user to still work with the application while you process data.
I think a better approach would be to take Dustin's route and selectively disable certain controls that can affect the background operation. Or make your background operation independent of the UI while it's processing.
If you tell us a little bit more about how your Main Window and Background thread interact we may be able to give you a better solution.
Hide all forms and only show the one main form. Then disable the Toolbar/Menu if you have either. Then have a status bar with a progress bar and when it gets done, unhide the form the user was working on.
When you are using a statusbar or a progress bar while your background thread is processing some longduring task, disabling your form will also disable your progress/status bar from updating. So what you should do in this case is disable every other control exept from the one that needs te be kept active (e.g. like a progressbar).
List<Control> lstControls = GetAllControls(this.Controls);
foreach (Control ctrl in lstControls)
{
if (ctrl.GetType().Name.ToLower().Contains("progressbar") {
ctrl.Enabled = true;
}
else
{
ctrl.Enabled = false;
}
}
Use a thread and display a modal dialog that shows the user the progress of your task and gives the user the option to cancel it.
The modal dialog will automatically prevent input (the parent may have to be the mdi window itself.)
(Please do not use hacks like hiding or disabling controls or windows. And please, please, please! do not use DoEvents.)
Related
I am using simple event handler in the while loop.
I have value change event for the boolean button. There is some code that takes 3-4 seconds to execute.
The problem is I am not able to click anything on my Front panel during this period. Is it possible to allow the user to click on other controls when event handler is working on some case (as I understand the event handler is able to collect all events and process them ASAP)?
I fully agree with Mikhail N Zakharov's answer, but anyway your problem can be easily solved by just unchecking the checkbox named Lock panel until the case for this event complates
Please see screenshot below.
PS. Once again it is not the best practise to make event structure to work for 3-4 seconds.
I think you need to restructure your application to make it more responsive. LabVIEW best development practices suggest keeping event handler code as fast as possible. One of the ways to handle this would be to send a message into the queue on the change of this Boolean control and process the queue in a separate loop.
I have a Control say for ex a Submit button if user clicks the button twice or more continuously then user receiving same message / same operation taking place twice or more.
I need to avoid this situation.
thanks for your inputs.
You need to detect the button click event either in the code behind of the view (or ViewModel if using the MVVM pattern) and disable the button. Now I take it that your submit button is firing off some kind of asynchronous operation. Once the asynchronous operation has successfully completed you will probably need to enable the button so that it is available again.
Shankar, if you want to avoid clicking on button, you should disable it. If you can give more details about what exactly you are trying to do, more details can be given.
I have a form in a vb.net windows form application called PolicyRefreshStatus.vb that has a ProgressBar control on it. From the main form called EditPolicy.vb I need to show PolicyRefreshStatus.vb over top of EditPolicy.vb - but the way things are wired I'm controlling the the ProgressBar and it's steps from logic inside EditPolicy.vb.
If I display the PolicyRefreshStatus.vb bar using the .show() method things work fine. The problem is if the user clicks back on the main form then PolicyRefreshStatus.vb losses focus. If I show PolicyRefreshStatus.vb as a modal form using .ShowDialog() then execution halts in EditPolicy.vb after the .ShowDialog() statement.
so for example in the code:
mPolicyRefreshStatus = New PolicyRefreshStatus
mPolicyRefreshStatus.pbMax = mPolicy.ClaimsUpdateMax
mPolicyRefreshStatus.ShowDialog()
mPolicy.UpdateFromFIS()
The line mPolicy.UpdateFromFIS() never executes because it's waiting for the PolicyRefreshStatus form to close.
How can I show PolicyRefreshStatus in a modal form but let execution continue in EditPolicy.vb?
You've got a couple of related options.
This first is to pass the unit of work to the progress bar in the form of a delegate or a class implementing an Interface. Something like this (not checked for correctness, just a rough example):
mPolicyRefreshStatus = New PolicyRefreshStatus
mPolicyRefreshStatus.pbMax = mPolicy.ClaimsUpdateMax
mPolicyRefreshStatus.UnitOfWork = AddressOf(mPolicy.UpdateFromFIS())
mPolicyRefreshStatus.ShowDialog()
Then within the progress form you can call back to the routine that actually does the work.
Another approach is to define events on your ProgressForm and then the owning/launching object can handle those events to do the work in. With this option you can create a fairly detailed set of events to be able to handle incremental work or cancels, but the concept is the same, youu are calling back from the progress form into launcher to perform the actual business logic.
You cannot show the form modally and let your routine continue. You must show the form Non-modally and then do your other stuff, closing the form when you've finished. Maybe a loop until the task has finished?
Using Show() with a parent form parameter will give you better usability. More like a tool window.
I'm having a weird issue with form painting in the Compact Framework. I have a login dialog that is basically a small form that is opened on top of another using ShowDialog. When a card is swiped, the login dialog is supposed to close, then some login tasks are performed and then the form behind it should be activated. The problem is that the form behind the login dialog is not being refreshed and so the login dialog will not be removed until after the form behind is refreshed by some user action. This is probably due to the heavy processing that goes on in the login tasks part, but I've not found a way to solve this.
Basically, I want a way to force the application to close the dialog and paint everything again, before performing the heavy login tasks. I've tried numerous refresh methods without any luck:
Form loginDialog = new Form();
DialogResult result = loginDialog.ShowDialog();
loginDialog.Dispose();
//I've tried everything at this point to get the form to refresh before performing
//login tasks
this.Refresh();
this.Invalidate();
Application.DoEvents();
PerformHeavyLoginTasks();
Does anyone know what could be going wrong? Thanks
Ok I figured this out. The problem was with a custom control on the background form that manually paints itself using rectangles and such. I think this is a compact framework bug since I called Refresh and Invalidate on that control as well and it should've repainted. I had to create a method that would call the control's OnPaint override directly since Invalidate and Refreshed were pretty much ignored.
The issue, I believe, is that you're not fully understanding what's going on system-wise here.
When your fore window (the Dialog) is dismissed, the background window (the Form) is given focu and tol to repaint the clipping region where the dialog was. This happens via a PostMessage call, which sends a Windows Message that has to be popped, translated and dispatched down in the bowels of the Application.Run call.
This is, by design, a fairly slow process as the UI should not be preempting things that are important.
If you are doing heavy processing immediately after that PostMessage happens, the processing of those windows messages can often be slowed, ending up with the UI appearing "locked" or drawing really slowly. This is exacerbated if the processing you're doing is on the same thread as the UI.
Why are your efforst not making things better?
Calling Refresh simply sends another message. That message now gets in line for processing, so it would actually make things worse.
Calling Invalidate does pretty much the same this as Refresh, just asynchronously. Again, it makes things worse.
DoEvents tells the message pump to pop, translate and dispatch a message. That dispatch still has to be processed on the UI thread, so noting is going to happen until the thread has time to do the work (i.e. after your processing)
So how do we "fix" this?
The first step is often to put the processing on a separate thread to allow the scheduler to round-robin tasks between the UI and processing threads, up to the default quantum. Thgis means that the processing can only starve the UI for a maximum of 100ms before some sort of drawing is allowed to occur (assuming equal thread priority).
new Thread(PerformHeavyLoginTasks)
{
IsBackground = true
}.Start();
You can go a step further and give the UI a "jump start" on the processing (of 10ms in this example):
new Thread(new ThreadStart(delegate
{
Thread.Sleep(10);
PerformHeavyLoginTasks();
}))
{
IsBackground = true
}.Start();
Of course this may mean you need to now handle the next "display" asynchrously if the UI you want to display is dependent on the processing result. There are plenty of online resources for async patterns, so I won't beat that dead horse here.
I have a DataGridView control in my Windows Forms Application.
I am adding rows to the grid using a background thread. I change the form's cursor to Waitcursor when the process starts and back to Default when it ends. This works well for the form, but not for the grid. When the form's cursor is changed back to default, the grid's cursor does not change, although the cursor over the rest of the form does.
Does this have anything to do with the fact that I am updating the grid from a background thread? (The cursor is being changed from the UI thread directly).
Edit: The background process raises an event, the handler checks the InvokeRequired property of the grid and decides if it needs to "Invoke" the method again from the main thread. So, in effect the actual UI update happens from the appropriate thread. I am not sure if this means that I am "using a background thread" or not. :|
I've had some problems doing single thread updating of my datagrids, where the datagrid did not reset to normal cursor after i've had waitcursor to true.
What I did was right after i went
this.UseWaitCursor = false;
I added
DatagridviewFoo.Cursor = this.Cursor;
Maybe it's just the same problem for you
I've had this problem as well. It was difficult to track down the cause, let alone a solution.
This issue only ever happened when I had a dialog box over the DGV control and the mouse clicked on a button to close the box such that when the box closed, the mouse was over a (resizable) column border. If the cursor ended up over a cell, the problem didn't arise. If I had to guess, I'd say the grid was seeing a column resize event as soon as the dialog box closed which wasn't properly handled.
Using Cursor.Current = Cursors.Default fixed my issue (without the need to explicitly reset the control's cursor). But maybe be aware that Application.UseWaitCursor = False didn't work even with the explicit control cursor reset.
I had a similar problem, but neither of the posted solutions worked for me. Mine was not caused by clicking a button above a movable column separator. It just randomly happened after opening and closing a dialog box. I'm pretty sure it came down to timing because .Net/Windows has issues when it comes to setting cursors and actually having them take effect. To try to overcome that, the library we use for showing and hiding the wait cursor calls - ack! - Application.DoEvents. I set a breakpoint in OnCursorChanged and saw that the cursor was sometimes actually getting set on a latter call to Application.DoEvents (used to keep the UI responsive while waiting for the file system to release a write lock on a file). So I guess sometimes the default cursor was getting turned back on before the call to set the wait cursor had fully taken effect. Anyway, my brute-force approach is to call
Cursor = Cursors.Default;
in my override of OnCellEnter (which always happens after the grid gets refreshed following the dialog box being closed). I'm not particularly proud of this, but it seems to work.