I have a simple form with a button and a progress bar. User clicks the button to begin processing and the progress bar animates while the code runs. In this case, it's just a for loop. But the problem is that the progress bar only appears for a fraction of a second then disappears.
private void button1_Click(object sender, EventArgs e)
{
progressBar1.Style = ProgressBarStyle.Marquee;
progressBar1.MarqueeAnimationSpeed = 100;
for (int i = 0; i < 3; i++) { Thread.Sleep(1000); } // sleep 3 times for 1 second
}
I assume this happens because the frame is redrawn after the code continues? So I tried running the for loop on another thread but it didn't seem to matter.
How can I get the bar to animate while the loop runs?
Thanks
You can simply workaround this by including a call to Application.DoEvents() on each iteration of your loop.
But this is not the best way to achieve this.
The recommended way is processing your loop inside another thread, like a BackgroundWorker, keeping your progressbar animating on the mainthread.
You can get some explanation here: Keeping your UI Responsive and the Dangers of Application.DoEvents
Related
I have this code:
private void button1_Click(object sender, EventArgs e)
{
var max = 0;
foreach (var address in textBox2.Text.Split(','))
{
max = +1;
}
var maxp = 100 / max;
foreach (var address in textBox2.Text.Split(','))
{
SendMessage(address);
progressBar1.Value = +maxp;
}
}
It calculates how many emails are in the textbox, and then makes a proportion. To each email sent adds the value of progress, the problem is that when I press the button, the progressbar does not move. When all emails are sent the progressbar moves to the end of stroke.
How can I do?
This happens because your loop and the ui are executing on the same thread. While the loop is busy, it can't update the ui
You can use a BackgroundWorker to run the loop on a different thread in the background, then use the BackgroundWorker's ProgressChanged event to update your progressbar. You can learn more about BackgroundWorkers here
Again you are executing code on a thread other than the UI thread. In WinForms you must invoke back to the UI thread and in WPF you must use application dispatcher.
WinForms:
Invoke((MethodInvoker) delegate {
DoSomethingOnUiThread();
});
WPF:
Application.Current.Dispatcher.Invoke(() =>{
DoSomethingOnUiThread();
});
You block the UI thread so it cannot refresh the UI until the processing leaves the method.
See three different solutions here with explicitly used threads, BackgroundWorker and async-await techniques.
I have some simple C# code that is triggered on a Button Press. The button press first clears some ListBoxes, then changes the text of a label, and then calls a function.
private void button1_Click(object sender, EventArgs e)
{
listBox1.Items.Clear();
listBox2.Items.Clear();
listBox3.Items.Clear();
listBox4.Items.Clear();
label5.Text = "Getting links...";
process(url);
label5.Text = "Finished";
}
But the Lists are cleared and the label is changed after process() is finished executing. This ruins the purpose as I'm changing the label so that the user is aware that some action is taking place. How can I make the initial label change before the function process() finishes?
If your process method is long-running, it can cause UI freezing and prevent UI from redrawing - that's why you don't see your label text immediate update.
Simpliest way to achieve your goal - is call label5.Refresh() right after label5.Text = "Getting links...";, this will immediately cause invalidation and redrawing of label.
Or even you can call this.Refresh() if more than one control should be updated - this will update whole usercontrol or form owns your controls.
But note - if your process method runs a very long time (more than a 2-3 seconds for example) - you should consider doing it asyncroniously in thread separate from UI. It is considered as "good style" because it will not cause UI freezing.
You can use async keyword. Only when accessing the UI from different thread you have to use the Invoke
private async void button1_Click(object sender, EventArgs e)
{
await Task.Run(
() =>
{
this.Invoke((MethodInvoker)delegate
{
listBox1.Items.Clear();
listBox2.Items.Clear();
listBox3.Items.Clear();
listBox4.Items.Clear();
myLabel.Text = "Getting links...";
});
});
this.process(url);
await Task.Run(
() =>
{
this.Invoke((MethodInvoker)delegate { myLabel.Text = "Finished"; });
});
}
What about using a Task to run process(url) in a "thread" separated from GUI?
In this way GUI will stay responsive to the user ang got "refreshed", then, when your task ends, you just have to update GUI label.
When you have ops that must take a bit of time, you should always separate them from GUI. My two cents.
You have 2 options. either use a different thread to run process(url), or add before it Application.DoEvents().
This question already has answers here:
Implementing a pause in WPF
(3 answers)
Closed 9 years ago.
I have a WPF app and I want to sleep for a second before displaying certain info on screen. So its.
1. Click a button.
Sleep 1 sec.
Display a label.
Sleep 1 sec.
Display a label.
etc etc
private void RunTest()
{
clearTable();
System.Threading.Thread.Sleep(1000);
this.Cursor = Cursors.Wait;
Label_OS_Result.Content = operatingSystem;
Image_OS.Visibility = Visibility.Visible;
System.Threading.Thread.Sleep(1000);
Label_CPU_Result.Content = procName;
Image_CPU.Visibility = Visibility.Visible;
System.Threading.Thread.Sleep(1000);
}
But when I click my button it seems to wait for a few seconds and then displays everything all at once.
Whats going on here??
It is working as it is expected.
Thread.Sleep stops the execution of the current thread for specified amount of time. So, when you change the visibility of an image, it will make further calls to change the visibility in the framework, then it will try to draw it on screen (invalidates). When you sleep the thread before this operation finishes it will not have enough time to finish this operation. You are simply blocking the UI thread responsible of drawing something on the screen.
Beware that Thread.Sleep may not be the solution, it is better for you to have a look at DispatcherTimer or BackgroundWorkers.
You don't want to Thead.Sleep() on the thread displaying your GUI.
Instead, you should try await Task.Delay(). This is similar to sleep, but it won't block the GUI thread.
This will allow all the rendering to still happen, while delaying the visiblity changes for your labels.
It is working as intended.
It may not be what you expected, but the problem here is your expectations.
What happens when you fiddle with properties on most visual controls, that should end up changing the appearance of the control, is first to make the internal adjustments to the controls properties (ie. data), and then trigger a redraw. To trigger the redraw, a message is usually posted to the message queue of the thread that owns this visual control.
This thread usually processes messages one at a time, be it a button click, mouse movement, or the paint messages that was just posted because you changed the image.
However, that thread is basically written like this (pseudo-code):
while (true)
{
var message = GetNextMessageFromQueue();
ProcessMessage(message);
}
The last time this loop was active, it started processing a message that ended up calling your code, the one that is now sleeping.
So basically, to get the message pump (the typical name of the code that implements this loop) to continue pumping messages, and thus process your paint message, is not to sleep.
You might want to separate your processing out to a different thread, or some other asynchronous way of doing things "in the background".
Note that you will get the same problem if you start doing any kind of lengthy processing in response to a button click or similar, without doing it on a background thread (or again, some other asynchronous way). The GUI will appear to have frozen.
This problem, however, is so common that Microsoft ended up building in special support for it in Windows. It used to be that a window just seemed to hang. Now, however, if the message queue "fills up", Windows will fade out the windows and tack on a caption to it indicating that it has stopped responding. Not a solution, but slightly better.
Sleep function is behaving correct.
Better you use a Timer to do so,
// Declare it in the constructor of the class
int level = 0;
Timer timer = new Timer
timer.Interval = 1000;
timer.Tick +=new EventHandler(timer_Tick);
private void timer_Tick(object sender, EventArgs e)
{
timer.Stop();
if (level == 0)
{
Label_OS_Result.Content = operatingSystem;
Image_OS.Visibility = Visibility.Visible;
++level;
}
else if (level == 1)
{
Label_CPU_Result.Content = procName;
Image_CPU.Visibility = Visibility.Visible;
++level;
}
else if (level > 1)
{
this.Cursor = Cursors.Default;
return;
}
timer.Start();
}
private void RunTest()
{
clearTable();
//System.Threading.Thread.Sleep(1000);
timer.Start();
this.Cursor = Cursors.Wait;
}
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 am currently trying to create a program that will show a slideshow of pictures from an ImageList with variable show times from a ListView, which is acessed through a numericUpDown, but when I click the button to start, nothing happens, until the time of the slideshow ends, where the last slide is shown, then disappears straight away (if i leave out "pictureBox1.Visible = false" at the end, it stays).
current code:
private void buttonSlideshow_Click(object sender, EventArgs e)
{
pictureBox1.Visible = true;
for (int s = 0; s < listView1.Items.Count; s++)
{
listView1.Items[s].Selected = true;
pictureBox1.Image = imageList1.Images[s];
DateTime later = DateTime.Now.AddMilliseconds((double)numericUpDown1);
while (DateTime.Now < later)
{
}
}
pictureBox1.Visible = false;
}
I have tried many versions of this (including using timers and switching code around) have no idea what is going wrong
numericUpDown1 is the duration of the slide, have been using integers for testing, still doesn't work
Doing this:
while (DateTime.Now < later)
Is blocking your UI thread. It can't redraw the screen while you are keeping it busy spinning it's wheels. Use a timer with a call back instead.
You'll need to rework your code slightly. Rather than use a for loop, define a variable for your current slide, initialize it to zero in your click handler, make your picture box visible, load the first picture and then start your timer.
In your timer handler, you'll increment the current index, check it against the length of you list of slides and, if you still have slides to display, load the next one and then start the timer again (or you can use a timer that fires repeatedly, although you might want to be careful that it doesn't fire again before you're done handling that last one). If there are no more slides left, just do you clean up and make your picture box invisible again.
One final note, be careful with which thread the timer is going to fire on. In win forms you can use System.Windows.Forms.Timer which fires on the UI thread and you won't have any problems. In WPF you can use DispatcherTimer which also fires on the UI thread. Other timers generally run in their own thread and you'll have to handle pushing anything that's supposed to update the UI back to the UI thread.