CODEWITHSUNDEEP
winformsf#
user7530757
user7530757

Reputation:

How to update Windows Forms after running them? C# or F#

With the code below I am trying to print i in the textbox every second, but it doesn't update the textbox. Am I missing something?

open System
open System.Drawing
open System.Windows.Forms
open System.Threading

let form = new Form()

let textBox = new TextBox()

textBox.Text <- "Hello, World."

form.Controls.Add textBox

Application.Run form

let rec main i =
    Thread.Sleep(1000)
    textBox.Text <- sprintf "Hello, World. %i" i
    form.Controls.Add textBox
    main (i + 1)

main 0

Upvotes: 0

Views: 730

Answers (1)

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236228

You should use System.Windows.Forms.Timer if you want to periodically update something on the form. Provide the desired interval of timer ticks, add a Tick event handler (which updates text in the text box), and start the timer:

let form = new Form()
let textBox = new TextBox(Text = "Hello, world.")
form.Controls.Add textBox

let mutable value = 0 // counter
let timer = new Timer(Interval = 1000) // this timer will fire tick events each second
timer.Tick.Add <| fun _ -> // you can ignore argument which is passed to handler
    value <- value + 1
    textBox.Text <- sprintf "Hello, World. %i" value

timer.Start()
Application.Run(form)

Why your sample does not work? First of all Application.Run blocks further execution until you close the opened form. But even if you'll use form.Show() to execute recursive function while the form is shown, you would see the form stuck and didn't update. Because you are freezing main thread by Thread.Sleep and form is not able to process events and repaint itself. form.Refresh() would allow you to see the updates, but between them, the form will be non-responsive. Also, you don't need to add textBox to form controls on each iteration.

Upvotes: 2

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