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Why does Thread.sleep() behave in this way
This is a simple code that i have written:
private void button1_Click(object sender, EventArgs e)
{
label1.Text = "first";
Thread.Sleep(1000);
label1.Text = "second";
}
When this code is executed and button is clicked, label1 displays text as only 'second' but not 'first'. I checked using break point, and statement label1.text="first" is executed but label does not display 'first'. Why is this so?
Because your code is running on the UI thread.
When your app is running and you're not clicking on things, the application's main thread is rushing around, waiting for events, processing Windows messages, and painting the screen. When you click your button, the app stops doing those things, and runs your function instead. While it's running your method, it can't paint the screen. Your function sets the label to "First", blocks the thread for a second, then sets the label to "second".
When you return, control passes back to the application, which is then free to repaint the form. It repaints it using the "second" label. The message loop never had chance to paint it with the "first" label.
You're running a single threaded application. Although the statement setting the label1 object's Text property to "first" has been executed, because you are causing the main application thread to pause, the "Windows Message Pump" is not being executed.
The problem is your a freezing the UI thread here.
The text "first" is set but then you put the main GUI thread to sleep - so the UI does not get painted.
After the sleep phase is over, the text "second" is set and the UI gets painted.
That's just the way Windows works, so you have to do that differently.
e.g. using Threads, or Backgroundworker
If you want delay use timers.
The reason why you don't see the result in UI is because Dipatcher's priorities. The Render task has lower priority than the execution.
This helps you: TIMERS!
DispatcherTimer dispatcherTimer = new DispatcherTimer();
dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
dispatcherTimer.Interval = new TimeSpan(0, 0, 0, 1);
dispatcherTimer.Start();
private void dispatcherTimer_Tick(object sender, EventArgs e)
{
//your code goes here
}
If you work in WPF you can try this:
private void button1_Click(object sender, RoutedEventArgs e)
{
label1.Text = "first";
Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.ContextIdle);
Thread.Sleep(1000);
label1.Text = "second";
}
Related
Hi I have been trying to add a button into my program that when you click the button it displays text in a label, waits so the user can read it, then exits the program. but if I run it and try it it only waits then exits without displaying text. sorry if that was a bad explanation I just got into coding. This is what I have.
private void button3_Click(object sender, EventArgs e)
{
label1.Text = "Text Here";
Thread.Sleep(500);
this.Close();
}
Call label1.Invalidate() to force the control to be redrawn. When you call Thread.Sleep, the UI thread will be blocked and not update.
If this doesn't work, try label1.Refresh() or Application.DoEvents();
private void button3_Click(object sender, EventArgs e)
{
label1.Text = "Text Here";
label1.Invalidate();
Thread.Sleep(500);
this.Close();
}
A more ideal solution would be to use a timer, another thread, or some kind of async event to run the code separately from your UI:
timer = new Timer();
timer.Interval = 500;
timer.Tick += (sender, e) => Close();
timer.Start();
or
new Thread(delegate() {
Thread.Sleep(500);
this.Close();
}).Start();
Also note that 500 milliseconds is a pretty short time, did you mean 5000 milliseconds, which is equivalent to 5 seconds? You may want to also take a look at Winforms: Application.Exit vs Enviroment.Exit vs Form.Close, as Close() closes the current window.
Instead of using Thread.Sleep which blocks the UI thread (and keeps it from updating with your text), its better to keep the UI responsive. This will keep the UI working and delay then close the application.
private void button3_Click(object sender, EventArgs e)
{
label1.Text = "Text Here";
Task.Delay(5000).ContinueWith((arg) => Application.Exit());
}
The Task is run in another thread, delays for the specified milliseconds (5000 or 5 seconds in this case) then continues with a call to close the application.
By the way, this.Close() works to close the application only if the form you are running it from is the "initial" form of the application. If you ran the same code from another child form, it would only close the form. The better thing to do if you want to actually close the application is to use the Application.Close() method. This gracefully closes the application. If you want to down-right terminate, you can use Environment.Exit(int).
I have a Console app that displays a WinForms Form.
In the Form, the user clicks button 1 and it runs a long subroutine. I want to have a button 2 that can kill the subroutine at any point. However, the UI freezes when I click button 1 until the subroutine has finished. How can I get the UI to not freeze?
Your long-running code is blocking the UI thread, so you can no longer click the second button, nor interact with the UI in any way until the code is finished executing.
You'll need to move your long-running code to a separate thread. There are various (and newer) ways of doing this, but one way is the BackgroundWorker. It's pretty easy to learn, and wraps some nice functionality, like cancelling the thread.
Here's a short WinForms app to demonstrate. You have to explicitly enable the ability for the thread to be cancelled. In this example, the while loop continues indefinitely, but checks every 100ms to see if there's a request for it to be cancelled. When you click the second button, the cancellation request is sent, and the thread ends.
public partial class Form1 : Form
{
private BackgroundWorker bg;
public Form1()
{
InitializeComponent();
bg = new BackgroundWorker
{
WorkerSupportsCancellation = true
};
bg.DoWork += (sender, args) =>
{
while (true)
{
Thread.Sleep(100);
if (bg.CancellationPending)
break;
}
MessageBox.Show("Done!");
};
}
private void button1_Click(object sender, EventArgs e)
{
bg.RunWorkerAsync();
}
private void button2_Click(object sender, EventArgs e)
{
bg.CancelAsync();
}
}
Following up on chouaib's comment, another nice thing about using the BackgroundWorker in a WinForms environment is that you can drop and drop it onto your designer, similar to a Menu, Timer, etc. You can then access its members in the "properties" panel, setting "WorkerSupportsCancellation" to true, subscribing to events, etc.
From your comment:
"is there a way to run this background process and be able to update the main userform? I keep getting the "cross-thread operation not valid control accessed from a thread other than the..." I want to run the long-running background operation, and have it update the main UI with text in a label (like a percentage of its progress)"
If you want to update the UI while the thread is running, you should do that from the ProgressChanged event. First, enable that option and subscribe to the event:
bg.WorkerReportsProgress = true;
bg.ProgressChanged += bg_ProgressChanged;
Then call ReportProgress() when you want to update the UI. You could pass back a percentage complete and some text, for instance:
bg.ReportProgress(50, "Almost there...");
Finally, update the UI from inside the event:
void bg_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
var message = e.UserState.ToString();
var percent = e.ProgressPercentage;
lblStatus.Text = message + " " + percent;
}
You need to make it multithreaded as suggested in the comments. The older way of doing this was manage your own thread. Then along came the background worker (cheap and easy). Now a days you have other options such as the Task Library.
Remember - anything the runs on the UI thread prevents the UI from sending and receiving events until that operation is finished.
Look into the BackgroundWorker component
private void buttonSave_Click(object sender, EventArgs e)
{
textBox1.Text = "DATA is being copied.";
//my own function to cpy files, working properly
copyDirectory(sourceFolderPath, destFolderPath);
}
Copying takes 3 seconds, but i cannot see TextBox with text="DATA is being copied. before it goes into the copyDirectory function", it only updates the text box after finishing copy, what is the Problem? i am not using another thread in copying.
This is because of how Windows Forms handles events. Windows Forms is executing all events synchronously. Which means that when a button is clicked, all code in all attached events are executed, before anything else happens.
This means that until the copying finishes (that is, the method returns), the textbox will not be visibly updated.
There are several fixes for this. One fix is to have the button click start a timer, that executes 100 milliseconds later. And then when the timer executes, perform the copying.
Another (my preferred) would be to execute the copyDirectory method inside a Task:
Task.Factory.StartNew(() => copyDirectory(sourceFolderPath, destFolderPath))
Note: This means that the code runs on a different thread, so if you want to update the textbox to say something like "Completed!" when it's finished, you'll need to do this
Invoke(new Action(() => textbox.Text = "Completed!");
I would like to change the backgroundcolor of a button for a couple of seconds to lime and then change it back to normal. For some reason it simply doesnt work, I have to wait for those seconds and some things I tested also work but the backgroundcolor isn't changed. This is what I've tried so far:
private void button1_Click(object sender, EventArgs e)
{
button1.BackColor = Color.Lime;
Thread.Sleep(2000);
button1.BackColor = SystemColors.Control;
}
Hopefully someone can help me out with this!
As Horaciux mentioned, you can make use of a Timer object to do this.
Alternatively, you can make use of await and Task.Delay, as mentioned by Jon Skeet in this answer.
private async void button1_Click(object sender, EventArgs e)
{
button1.BackColor = Color.Lime;
await Task.Delay(2000);
button1.BackColor = SystemColors.Control;
}
The problem with Thread.Sleep is that it is a blocking operation - in that it will stop anything happening on the thread in question. There are other issues too though - chiefly that Thread.Sleep doesn't guarantee reactivating the thread in the time specified. When you execute Thread.Sleep, you are basically telling the CPU that your thread doesn't need to be active for the time specified - however, the CPU only guarantees that it won't process it for that time - it doesn't guarantee that it will reactivate at that time, merely at some point after the sleep period (once it has finished processing any other threads currently active).
Since you are adding Thread.Sleep to your UI thread, you are effectively locking up the entire application for the duration of the sleep. await Task.Delay on the other hand, won't block the thread, but will return to that line of code in the function once the task in the await has completed (in this case, a Delay action). This allows all other methods to continue to operate as normal (button clicks will work fine, etc). This method has the added advantage of keeping all the relevant code in one place, rather than having part of it in a different method.
You need a timer.
Add a timer control from the toolbox to your form. Double-click on it to add a timer tick event handler
private void button1_Click(object sender, EventArgs e)
{
button1.BackColor = Color.Lime;
//Set time between ticks in miliseconds.
timer1.Tick=2000;
//Start timer, your program continues execution normaly
timer1.Start;
//If you use sleep(2000) your program stop working for two seconds.
}
//this event will rise every time set in Tick (from start to stop)
private void timer1_Tick(object sender, EventArgs e)
{
//When execution reach here, it means 2 seconds have passed. Stop timer and change color
timer1.Stop;
button1.BackColor = SystemColors.Control;
}
Or you could use a Storyboard if you're working with a XAML technology. I ain't posting implementation details, since they may vary depending on the target technology.
I am trying to create a windows form that gets displayed for 2 seconds when triggerd by an event, and then closes automatically.
I have tried several options. This is my current code:
this.aletPopup.StartPosition = FormStartPosition.CenterScreen;
this.aletPopup.Show();
Thread.Sleep(2000);
this.aletPopup.Close();
This preforms the actions that I desire, however, when the form loads it does not load the label or image which is on the form. Instead, the area where the image and label are become transparent. My desired output is this:
I have also tried using this.aletPopup.ShowDialog();, which does display the graphics. However, the form will not close automatically when using this method.
EDIT: I am attempting to use
Michael Perrenoud's solution. However, I cannot get the form to close. I have a timer set at a 2000ms interval which is initally disabled. Am I overriding the OnShown correctly?
public AlertPopForm()
{
InitializeComponent();
}
private void closingTimer_Tick(object sender, EventArgs e)
{
closingTimer.Enabled = false;
this.Close();
}
private void AlertPopForm_OnShown(object sender, System.EventArgs e)
{
closingTimer.Enabled = true;
closingTimer.Start();
}
Instead, how about leveraging ShowDialog, and then using a Timer on the dialog form. In the Tick event of the Timer, close the form.
this.aletPopup.StartPosition = FormStartPosition.CenterScreen;
this.aletPopup.ShowDialog();
You could even pass the interval into the .ctor of the dialog form if you wanted some flexibility.
It's very important to note here that you'd need to leverage the OnShown override to actually Start the Timer so the form is in fact shown to the user.
The reason can be in Message Loop. When you block your thread by Thread.Sleep, it also blocks Message loop.
You can make like this:
this.aletPopup.StartPosition = FormStartPosition.CenterScreen;
this.aletPopup.Show();
for(var i = 0; i<= 200; i++)
{
Thread.Sleep(10);
Application.DoEvents();
}
this.aletPopup.Close();
DoEvents will process messages from message queue during that time.
When calling Thread.Sleep you're blocking the UI thread, thus preventing it from processing UI events.
You need to ensure that Close is called after 2 seconds without actually blocking the main thread. There are a number of ways of doing this, such as using a Timer, or something like Task.Delay:
aletPopup.StartPosition = FormStartPosition.CenterScreen;
aletPopup.Show();
Task.Delay(TimeSpan.FromSeconds(2))
.ContinueWith(t => aletPopup.Close(),
TaskScheduler.FromCurrentSynchronizationContext());
The reason this is happening, is that you are halting the thread that draws the form. So the form has time to display, but as it's being drawn, the thread is being stopped.
Easy enough to fix....
Add an event handler to the popup for the Load event with the following handler:
private async void handleLoad(Object sender, EventArgs args)
{
await Task.Delay(2000);
Close();
}
Remark
Because you used Show(), the user could always click around this popup. If this is undesirable, then use ShowDialog() instead.
Did you try a refresh to redraw the form?
this.aletPopup.StartPosition = FormStartPosition.CenterScreen;
this.aletPopup.Show();
this.alertPopup.Refresh();
Thread.Sleep(2000);
this.aletPopup.Close();