winform c# onPaint() block UI

Hieu Ha

I have two UserControls which added in a form in my winforms project, one with the function to draw a string and make it scrolling from right to left and the other draw another string and make it scroll from bottom to top over and over again controlled by calling Invalidate() inside a while(true) loop.But when one of my string becomes too long, about 1000 characters the UI Thread is blocked, so my questions are: What am I doing wrong? is there a better way to make text scrolling??? and bellow is my snippet of code:

int scrollTextSpeed = 100;
bool scrollingText = true;
Thread updateUI ;
void init()
{
updateUI = new Thread(updateScrollText);
updateUI.Start(); } void updateScrollText() { while (true)
{
if (scrollingText)
{
Dispatcher.CurrentDispatcher.Invoke(DispatcherPriority.Normal, new MethodInvoker(Invalidate)); Thread.Sleep(scrollTextSpeed);
}
}
}
protected override void OnPaint(System.Windows.Forms.PaintEventArgs e)
{
SizeF stringSize = e.Graphics.MeasureString(text, this.Font);
var yPos = (this.ClientSize.Height / 2) - (stringSize.Height / 2);
e.Graphics.TextRenderingHint = TextRenderingHint.AntiAlias; e.Graphics.DrawString(text, this.Font, brus, currentPos, yPos);
if (fisttime)
{
currentPos = this.ClientSize.Width - 1;
fisttime = false;
}
else
{
if (currentPos < (-1 * (stringSize.Width)))
currentPos = this.ClientSize.Width - 1;
else
currentPos -= scrollPixelDistance;
}
}

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Amit Gupta8y ago
I Had made a control based on a thread, you can download it and use it freely, which gives much smoother performance.

https://agsoftwares.weebly.com/uploads/4/5/7/3/4573025/xtimer.dll
Hieu Ha8y ago
hey Amit Gupta, Itried two solutions before: 1- using a label and change its location in a separate thread, it was not running smooth as draw text in onpaint() does and still block ui if text indise label is too long. 2 - using timer and change label location every timer tick,but the result the same as the solution number one.
Amit Gupta8y ago
Hey

Scrolling text on paint function is a hude degradation in the performance and causes your UI to be freezed as you are using a infinity while loop, you can call Application.DoEvents() to do some other operations on the intetface but I discourage you to do this.

Take a label, write your text there and use a timer control or a seperate thread for scrolling purpose, this will make your interface responsive.

Win forms usea Gdi+ for rendering controls which paints all the control over the screen which is much slower in its performance.

Good Luck