In my c# winform app I have a button which when clicked, it performs some calculations which can tke some time.
I also have a label.visible = false which I would like to label.visible = true right after the button click so that the user can see the app working away.
The thing is even when label.visible = true is the first thing in the button1_Click(object sender, EventArgs e) method, it only toggles to visible at the very end, after the calculation is performed.
How can I show the label right after the button_click?
If you need your application to remain responsive whilst your app is processing, take a look at Background Worker
You can force your form to update & process any background messages by calling:
Application.DoEvents();
Just after you have changed your label - although this is probably a bit of a hacky solution.
Your calculation is being performed on the UI thread. This means that it is blocking the UI from refresshing after you have set the visibility of the label.
You should consider doing the calculation on another thread using a Task. This will allow the UI to be responsive during what it seems is a long operation that can run in the background.
e.g.
var taskCalc = Task.Factory.StartNew(() => //Do Calculation );
There are several ways to tackle this.
One way (the simplest) is to call
this.Refresh();
right after you set the Label to visible.
Another is to do your calculations in a background thread. The easiest way to do that is to use a BackgroundWorker. Then your main thread can just continue serving the UI (refreshing the form, responding to buttons etc.) while the background worker thread performs the computation.
See http://www.dotnetperls.com/backgroundworker for more on background worker threads.
Like others have said: You are performing your work on the UI Thread. I am showing you another valid way of achieving what you need. You can move your work to a separate thread using an anonymous delegate.
(new System.Threading.Thread(() =>
{
dowork(); // What ever work you need put here.
})).Start();
Related
This code imitates the problem that I am experiencing in my app.
private void button1_Click(object sender, EventArgs e)
{
button1.BackColor = Color.Red;
Thread.Sleep(3000);
button1.BackColor = Color.Green;
}
I would expect this code to;
Make button red
Wait 3s
Make button green
but instead It is waiting 3s and then making button green. I can't just make the button green from the start as this would not work in my bigger app.
Does anyone have any idea what is wrong and also how i could fix it? Thanks in advance.
No. it's changing to Red but you are blocking your UI thread and thus you don't see the color changed. What if you change the handler to a async one like
private async Task button1_Click(object sender, EventArgs e)
{
button1.BackColor = Color.Red;
await Task.Delay(3000);
button1.BackColor = Color.Green;
}
The problem is that with Sleep you are blocking the main (rendering) thread. So you set the button red, but because you are blocking the thread, the app can't render it. In fact, I expect that the whole application freeze.
I am not sure what are you using, but try to look at some timers.
EDIT or simply use tasks Delayed function calls. Just do not use threads, please.
The technical reason for this, is the UI works on a Message Pump (in the case of WinForms, or similar in regards to WPF). Basically a message pump is a queue of work items to do, and a while loop like the following:
while(GetMessage(&msg, NULL, 0, 0) > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
What is happening, is that when you are processing your click:
The click goes into the message queue
Gets processed by the message pump
Goes into your click method
Blocks the thread for x amount of seconds, its still in your method and the pump can't process.
Why?
Thread.Sleep()
Suspends the current thread for the specified amount of time.
In short, no other messages get processed. In your example you sleep the thread before the pump has had time to process your colour change yet (its still stick processing your click).
When the messages eventually process, it goes through the backlog (your color changes being part of that), then without pause quickly changes it from one to the other.
The fix is quite simple, you need to allow your pump to process messages while you wait and as the other answers have eluded to, in modern version on .net we can use the async await pattern, and take advantage of the Task.Delay() method.
When the program process anything that is prefixed with await,
If you are on the UI thread it captures the context
Starts another thread with a continuation,
lets the message pump continue processing.
When the task has finished (and your delay is over), it returns control back to the original context (the thread you called it from).
Hey presto. Everything is as it should be.
When my main form loads I want to do some processing like loading the last client viewed. This extra processing causing the drawing of the form to be pretty ugly. I am doing it on form shown so I would expect that the form would be done painting.
I have used PostMessage... Is there a modern day version of PostMessage? During this processing I would like to set the hourglass cursor.
I think what you are trying to do is background processing. So you can use a BackgroundWorker class. When your form loads, you would start the background worker and when the worker is finished, it will notify your form through the RunWorkerCompleted event. You can even get progress updates from the worker by implementing ProgressChanged event.
How about using Task + ContinueWith. (If you upgrade to .Net 4.5 async/await would be a better choice).
private void Form_Load(object sender, EventArgs e)
{
Task.Factory.StartNew(() =>
{
Thread.Sleep(5000); //Some long Running Jobs
return "Finished";
})
.ContinueWith(t =>
{
this.Text = t.Result; //Update GUI
},
TaskScheduler.FromCurrentSynchronizationContext());
}
I am not sure why would you want to use PostMessage. If you post a message using PostMessage it will eventually be obtained by GetMessage and unless the message is posted from a different thread whole exercise seems a little futile. Am I missing something here? As for BackgroundWorker please refer to the solution for Label is not set until method is done.
I have a long calculation that happens in a button click event, and after each iteration, I want the progress bar to update. I was wondering if there is any way to do this without using a background thread:
private void btnGetData_Click(object sender, RoutedEventArgs e)
{
progressBarGetData.Minimum = 0;
progressBarGetData.Maximum = recordCount;
progressBarGetData.Value = 0;
while(long iteration going on)
{
//do work
progressBarGetData.Value += 1;
}
}//end button click
The progress bar doesn't increment slowly on the screen. Do I have to use a background worker?
Thank you.
It's not the progress bar that's the main problem - it's the fact that you're performing a long-running synchronous operation in the UI thread. That will freeze the whole UI, giving a terrible user experience.
If you can convert your loop to use asynchronous calls (e.g. if it's only long-running because it's talking to web services or a database) then that's one option - and one which is made much easier in .NET 4.5.
Otherwise, you will need a separate thread - either started explicitly or using BackgroundWorker.
I want to have a loading form showing up while the main app connects to db and fetching initial data. Because this can take up 5-10 secs I want to inform the user that something is happening.
This is what I have come up with:
frmStart _frmStart = new frmStart();
Thread t = new Thread(() => _frmStart.ShowDialog());
t.Start();
objDAL = new DBManager();
objDAL.conSTR = Properties.Settings.Default.conDEFAULT;
PrepareForm();
t.Abort();
Is this the best way?
No, this doesn't solve the frozen UI problem, it merely papers it over. Imperfectly at that, the dialog's parent is the desktop and can easily appear underneath the frozen window and thus not be visible at all. And the dialog isn't modal to the regular windows since it runs on another thread. The failure mode when the user starts clicking on the non-responsive window is very ugly, those clicks all get dispatched when the UI thread comes back alive.
There are workarounds for that (you'd have to pinvoke SetParent and disable the main windows yourself) but that's just solving the wrong problem. You should never let the UI thread block for more than a second. Use a BackgroundWorker to do the heavy lifting, update the form with the query results in the RunWorkerCompleted event handler.
If you are using WinForms you may want to take a look at this A Pretty Good Splash Screen in C#. If you are using WPF you could take a look at this Implement Splash Screen with WPF.
I have a main form that contains an edit control that occupies the entire form. There is another worker thread that constantly writes log messages to this edit control. Now I want to show a dialog box with just a cancel button while the main UI's edit control is displaying stuff. The problem is that the cancel dialog is non-responsive while the updates are happening behind it and I cannot click on the cancel button. Any idea on how to resolve it. I was thinking of creating another UI thread and show the cancel button from it. Any other alternatives?
EDIT#1
I should clarify that I already use a worker thread to do the work.
DisplayLogs() is in a seperate thread.
DisplayLogs() is called from other threads.
LogMessage is the delegate that points to the method UpdateMessage in main UI.
The control used is a TextBox. I have tried other controls like listview,
richtextboxsand, etc. still the same result.
Worker Thread
void DisplayLogs()
{
lock (this)
{
while (logQueue.Count > 0)
{
string logMessagemessage = logQueue.Dequeue();
LogMessage(string.Concat(logMessagemessage, Environment.NewLine));
}
}
}
Main UI
public void UpdateMessage( string message)
{
if (!txtLog.IsHandleCreated)
{
return;
}
if (txtLog.InvokeRequired)
txtLog.BeginInvoke( new UpdateLogDelegate( UpdateLog), message);
else
txtLog.AppendText(message);
}
The main solution is to offload the expensive code onto a background worker and leave your UI thread responsive for UI actions. Your form can then simply show a modal dialog or something.
MSDN - How to use a Background Worker
In this situation it's necessary to move the majority of the work to a new thread, and clear up the UI thread for cancel messages etc.
You are going about this backwards. The main thread should, in theory, always be available to accept user input. Anything that may block for extended periods of time (heavy computation, database access, network access) should be done in a background thread. The idea is to have the edit control's data being computed and populated by a background thread (BackgroundWorker objects work nicely here) so that the main thread is always available if the user clicks on the cancel button.
Your problem is that the your UI thread is ALWAYS busy. I am saying this assuming that the number of items in logQueue is quite large. The while loop doesn't quit till the queue is empty. So it keeps hitting the UI thread with request for updates.
Also the if (txtLog.InvokeRequired) is kind of pointless because you are always calling the method from a worker thread.
So, since a .net WinForm application has only a single UI, which in your case is too busy to process other notifications, the new window appears stuck (because the paint messages are stuck in the message queue and cannot be processed as it is already flooded with the text box update messages)
You could stick an Application.DoEvents inside your loop which will give the message loop some time to process the pending notifications. However this is kind of a hack, in my opinion, as the UI behavior is sometimes not predictable. It may lead to things like stuttering while moving a dialog, delayed responses to click events etc.
Another point, MessageBox.Show or a Form.ShowDialog (if this is what you are using for the cancel button) is a blocking call. The thread on which you show it WILL hang till you dismiss the dialog. Try Form.Show and set the parent property to the main form.
Another alternative is to add a timer and process only X notifications per Y seconds. This will give the UI thread some breathing room for performing other activities.