How does WPF decide how to render the textblock textwrap?

Question

I'm trying to get my head around how WPF makes decisions when it renders a textblock with wrap enabled.

I have the following code:

<Window x:Class="WpfWrapTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Width="200" Height="200">
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" MinWidth="5"></ColumnDefinition>
        <ColumnDefinition Width="Auto"></ColumnDefinition>
        <ColumnDefinition Width="Auto"></ColumnDefinition>
    </Grid.ColumnDefinitions>
    <Border Background="Yellow" Grid.Column="0"></Border>
    <GridSplitter ResizeDirection="Columns" Grid.Column="1" Width="3" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"></GridSplitter>
    <Grid Grid.Column="2" MinWidth="40">
        <TextBlock  TextWrapping="Wrap">asdflk;jsadlkfjlaskdjflasdkjflk laskdjfl;askjd l;kasjdf l;kjsadf ;lkajsdfl k</TextBlock>
    </Grid>
</Grid>

When starting WPF decides to make my textblock larger than the screen and not take this into account for wrapping

Then when I drag the gridsplitter it somehow makes a different decision (probably because the gridsplitter is setting a width of a neighbour control?)

A third weird behaviour in this sample is when you try to drag the gridsplitter more left than it can go (minwidth on column 1 is 5). Then it decides to re-enlarge the textblock outside the visual screenspace.

What is making WPF do one or the other?

Answer 1

Try setting the 3rd column with to "*" instead. "Auto" means that the TextBlock will use as much space as it needs, effectively meaning it doesn't need to wrap.

When you drag the splitter, you are giving the grid column an explicit size, so TextBlock will wrap to fit to that size.

Answer 2

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" MinWidth="5"></ColumnDefinition>
            <ColumnDefinition Width="Auto"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Border Background="Yellow" Grid.Column="0"></Border>
        <GridSplitter ResizeDirection="Columns" Grid.Column="1" Width="3" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"></GridSplitter>
        <Grid Grid.Column="2" MinWidth="40">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"></ColumnDefinition>
            </Grid.ColumnDefinitions>
            <TextBlock  TextWrapping="Wrap">asdflk;jsadlkfjlaskdjflasdkjflk laskdjfl;askjd l;kasjdf l;kjsadf ;lkajsdfl k</TextBlock>
        </Grid>
    </Grid>
</Window>

Answer 3

It's quite simple really... probably too simple for an answer even.

If the TextBlock or a parent of the TextBlock is given a Width that the TextBlock.Text value is longer than, the text will be wrapped. Otherwise, it will not be wrapped.

It really is that simple. As for the other 'weird' symptoms that you spoke about, I can't really help you there... your code didn't show me them. For example, I'm not sure how you can drag a GridSplitter more left than it can go .