Poor TextBox performance with wrapping on and large amounts of data

Question

I have a persistent problem with textboxes in WPF, using .NET 3.5. With a large (5000+ lines) amount of data in a TextBox with wrapping enabled, the window has ridiculously bad performance while being resized.

This only happens with TextWrapping="Wrap". Having the text data bound or just setting it programmatically makes no difference.

The code is literally as simple as this:

<TextBox Margin="12,39,337,29" Text="{Binding Output, Mode=OneWay}" TextWrapping="Wrap" VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Disabled" />

The text is bound to a single string. The bound data is not being changed.

Edit: The data is not being changed while the window is resizing, is what I meant. It will be updated in the future. The TextBox does not need to be editable, but the actual text does need to be selectable. /Edit.

I've had a quick play with AvalonEdit, which has the same problem. It seems strange that I can't find any other threads which describe this issue.

Any advice?

Thanks, Rich

Answer 1

The part that is slow is displaying all that text at once. I have run into this issue before where the TextBox in my control became very large and had a ScrollViewer for the whole control that would handle the very large TextBox.

You are almost doing that, but without setting a max for your height/width, I'm not sure if your ScrollViewer is actually going to be utilized.

My solution is to use the built-in scrollViewer inside of your TextBox(which you are doing), and then limit the size of the textbox height/width so that it isn't trying to render 100% of the text all at once (and actually utilizes the ScrollViewer inside your TextBox)

(FYI, I also like using CanContentScroll=true, though I don't think it will affect the speed)

<TextBox Margin="12,39,337,29" TextWrapping="Wrap" 
         Text="{Binding Output, Mode=OneWay}"
         ScrollViewer.CanContentScroll="true"
         VerticalScrollBarVisibility="auto" 
         HorizontalScrollBarVisibility="auto" 
         MaxHeight="600" MaxWidth="600"/>

Answer 2

You could react to the windowResizeStart event and disable wrapping for the text block. Then wrap just once when the resize completes.

You gain performance but lose some visual flair I guess.