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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;
}
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.
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();
In my application, I have two text boxes accompanied with two labels: "Connected" and "Not Connected". As seen in my code, if a connection is established, the "Connected" text box will fill with Green, indicating a network connection. It will be red if not.
The functionality of connection detection is working just fine, however, I have to re-open the application for it to detect the change. I am looking for a way to refresh the application every 5-10 seconds or so automatically to detect any change in connectivity. I don't want to flush out the contents of any other field or box, just the color text boxes. A soft polling loop so to speak. How would I go about doing this using the Timer method. Should I create a new thread in which to run the timer and refresh the box?
Thanks.
if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable() == false)
{
noConnect.Select(); //if not connected, turn box red
noConnect.BackColor = Color.Red;
}
else
{
netConnect.Select(); // if connected, turn box green
netConnect.BackColor = Color.Lime;
}
//need to refresh box/application without losing other box/field contents
//in order to constantly check connectivity around 5-10 seconds or so
//constantly check connectivity
Something like this would work
public Form1()
{
InitializeComponent();
var timer = new Timer();
timer.Tick += new EventHandler(timer_Tick);
timer.Interval = 10000; //10 seconds
timer.Start();
}
void timer_Tick(object sender, EventArgs e)
{
if (your_function_call())
{
netConnect.BackColor = Color.Green;
}
else
netConnect.BackColor = Color.Red;
}
The timer_Tick would be repeatedly called every interval and you can poll your status and update controls. Because the timer call back is called in the UI-thread you can update any UI elements.
From Timer Class
A Timer is used to raise an event at user-defined intervals. This
Windows timer is designed for a single-threaded environment where UI
threads are used to perform processing. It requires that the user code
have a UI message pump available and always operate from the same
thread, or marshal the call onto another thread. When you use this
timer, use the Tick event to perform a polling operation or to display
a splash screen for a specified period of time. Whenever the Enabled
property is set to true and the Interval property is greater than
zero, the Tick event is raised at intervals based on the Interval
property setting.
This solution uses System.Windows.Forms.Timer that calls the tick on UI-thread. If you use System.Timers.Timer the callback won't be on UI-thread.
just create the timer. it well run on his own thread without you doing any thing else.
You can create a timer somewhere in your application
var timer = new System.Timers.Timer();
timer.Interval = 5000; // every 5 seconds
timer.Elapsed = (s, e) => {
// Your code
};
timer.Start();
Note: please be aware that your code in the Elapsed event handler can/will run on another thread!
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.
I need to be able to disable a button for 1.5 seconds at a time for an application I'm writing. An image is displayed, a user clicks a button, and then another image is displayed. I need to make sure that the user doesn't click the button again too quickly.
So, when the image is displayed, I call this function:
//when a new image is displayed, start the timer and disable the 'done' button
//for 1.5 seconds, to force people to stop pressing next so quickly
System.Timers.Timer mTimer;
void TimerStart() {
Done.IsEnabled = false;
mTimer = new System.Timers.Timer();
mTimer.Interval = 1500;
mTimer.Start();
mTimer.Elapsed += new System.Timers.ElapsedEventHandler(TimerEnd);
}
The TimerEnd code looks like:
void TimerEnd(object sender, EventArgs eArgs) {
if (sender == mTimer){
Done.IsEnabled = true;
mTimer.Stop();
}
}
The 'Done.IsEnabled' line gets hit, but the button is not reenabled and the timer doesn't stop firing. What am I doing wrong here? If it matters, this is a WPF app.
Use DispatcherTimer instead
DispatcherTimer timer = new DispatcherTimer();
timer.Interval = TimeSpan.FromMilliseconds(someInterval);
timer.Tick += new EventHandler(someEventHandler);
timer.Start();
private void someEventHandler(Object sender, EventArgs args)
{
//some operations
//if you want this event handler executed for just once
// DispatcherTimer thisTimer = (DispatcherTimer)sender;
// thisTimer.Stop();
}
Basically you are trying to debounce the button, to prevent too quick clicks. Rather than use a timer save the previous click time in millis, if the button is clicked again within a short time ignore the next event.
The timer event is raised on a different thread. When working with the winforms controls, you need to make sure you Invoke them from the same thread where they were called.
When working with WPF there is no guarantee that updates made to UI controls on non-UI threads will work as expected. In many cases you will get an exception when you do this.
In your Timer elapsed handler you need to use the BeginInvoke/EndInvoke paradigm and put your button enabling logic in there to ensure that this code runs on the UI thread instead of Begin/End Invoke
There is a SynchnornizationContext available as well which can be accessed by calling SynchronizationContext.Current . You'll need to cache this before you make the timer call since SynchronizationContext.Current will be null in non-UI threads.
This link talks about this as well.