What does * mean in XAML

Question

What does * mean in XAML. I have a grid of width 400. And divided the grid to 3 columns. What does *.4 mean? I thought it is 40% of the space available. so thought the first 2 columns will get 40% percent each and the rest is taken by the third column. but looks like, the third column is taking 60% and the first two are getting 20% each. How does this work?

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width=".4*"/>
        <ColumnDefinition Width=".4*"/>
        <ColumnDefinition />
    </Grid.ColumnDefinitions>
</Grid>

Answer 1

Basically, the default is "1*", so what you have above is effectively:

<Grid.ColumnDefinitions>
    <ColumnDefinition Width="0.4*" />
    <ColumnDefinition Width="0.4*" />
    <ColumnDefinition Width="1.0*" />
</Grid.ColumnDefinitions>

The Star grid spacing (GridUnitType.Star) proportionally distributes space. In your case, you have a total of 1.8 (1.0 + 0.4 + 0.4), so the first two columns each get 22.2% (0.4/1.8) of the width allocated to them.

To get what you want, you can use:

<Grid.ColumnDefinitions>
    <ColumnDefinition Width="0.4*" />
    <ColumnDefinition Width="0.4*" />
    <ColumnDefinition Width="0.2*" />
</Grid.ColumnDefinitions>

This sets the total to 1.0, so each becomes a percentage.

Note that this will give exactly the same result as doing:

<Grid.ColumnDefinitions>
    <ColumnDefinition Width="40*" />
    <ColumnDefinition Width="40*" />
    <ColumnDefinition Width="20*" />
</Grid.ColumnDefinitions>

Since the total proportions are divided up by the total (100) now, still giving 40%, 40%, 20%.