Question

I’m writing a UI app that allows the user to paste a grid of numbers into it that will be sent to a remote server. Client could be WPF or Silverlight.

I’ve tried a Grid of Textbox controls using DataObject.AddPastingHandler to hook the user pasting input, converting from tab-separated rows in a string to Textbox controls. This takes 12 seconds (!) to update itself after the user pastes in just 122×161 cells from Excel which is unacceptably slow. Dissecting the string takes 0.1s, adding the rows and columns takes 1s, constructing and inserting the TextBox controls takes 2s and the remainder of the 12s appears to be spent drawing the TextBox controls for the first time.

I’ve also tried DataGrid but it doesn’t seem to handle 2D arrays well, preferring a 1D array of objects that it dissects for properties using reflection.

Now I’m contemplating just using a Canvas and drawing the numbers myself, which seems insane. Is there a simple way to use built-in WPF or Silverlight controls to get this done without painful lag for the user?

EDIT

I’ve since identified TextBox as the culprit because it is insanely slow. Here’s some F# code that illustrates the problem (replace TextBox with TextBlock and its 40x faster, which is still orders of magnitude slower than it should be but is acceptable in this instance):

open System.Windows

let app = Application()

let readClipboard() =
  let data = (Clipboard.GetData "Text") :?> string
  [|for row in data.Split[|'\n'|] do
    match row.Split[|'\t'|] with
    | [||] | [|""|] -> ()
    | row -> yield row|]

[<System.STAThreadAttribute>]
do
  let grid = Controls.Grid()
  let row = Controls.RowDefinition()
  Controls.RowDefinition() |> grid.RowDefinitions.Add
  Controls.ColumnDefinition() |> grid.ColumnDefinitions.Add
  let add i j ctrl =
    Controls.Grid.SetRow(ctrl, i)
    Controls.Grid.SetColumn(ctrl, j)
    grid.Children.Add ctrl |> ignore
  let paste() =
    let timer = System.Diagnostics.Stopwatch.StartNew()
    let data = readClipboard()
    printfn "Read clipboard %fs" timer.Elapsed.TotalSeconds
    let rows = data.Length
    let cols = data |> Array.fold (fun n xs -> xs.Length |> max n) 0
    printfn "%dx%d" rows cols
    grid.RowDefinitions.Clear()
    grid.ColumnDefinitions.Clear()
    grid.Children.Clear()
    for row in 1..rows do
      Controls.RowDefinition(Height=GridLength 24.0) |> grid.RowDefinitions.Add
    for col in 1..cols do
      Controls.ColumnDefinition(Width=GridLength 64.0) |> grid.ColumnDefinitions.Add
    printfn "Add rows and columns complete %fs" timer.Elapsed.TotalSeconds
    for i in 0..rows-1 do
      for j in 0..data.[i].Length-1 do
        Controls.TextBox(Text=data.[i].[j]) |> add i j
    printfn "Insert complete %fs" timer.Elapsed.TotalSeconds
    Media.CompositionTarget.Rendering.Add(fun _ ->
      printfn "Next Rendering event at %fs" timer.Elapsed.TotalSeconds
      app.Shutdown())
  let scroll = Controls.ScrollViewer(Content=grid)
  scroll.HorizontalScrollBarVisibility <- Controls.ScrollBarVisibility.Visible
  let window = Window(Content=scroll)
  window.Focusable <- true
  window.Focus() |> ignore
  window.PreviewKeyDown.Add(fun e ->
    let ctrl = Input.ModifierKeys.Control
    if Input.Keyboard.Modifiers &&& ctrl = ctrl then
      if e.Key = Input.Key.V then
        paste())
  app.Run window |> ignore

Answer 1

Turns out the problem is the built-in WPF TextBox control which is extremely slow. So we must either avoid it or replace it.

In this case, I just wanted text so I can avoid it by using TextBlock instead, which brings the time to paste the cells down from 12s to 0.25s which is (just about) acceptable.

For anyone who wants editable cells, apparently you should use TextBlock everywhere and only convert the one cell being edited to a TextBox because it is so slow.