How to collapse a star sized grid column in WPF?

Question

Getting three columns have the same width is done by setting Width to Auto.

<Grid x:Name="myGrid">
  <Grid.RowDefinitions>
    <RowDefinition Height="Auto" />
  </Grid.RowDefinitions>

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

  <Label Grid.Row="0" Grid.Column="0">One</Label>
  <Label Grid.Row="0" Grid.Column="1" x:Name="label1">Two</Label>
  <Label Grid.Row="0" Grid.Column="2">Three</Label>
</Grid>

I want to achieve that if middle column is collapsed or hidden that the other two take up remaining space and get equal width.

If I just set Visibility to Collapsed or Hidden because of the Width="*", the other two columns width stays the same.

<Label Grid.Row="0" Grid.Column="1" Visibility="Collapsed">Two</Label>

I achieved desired functionality by programatically setting second column width to auto, but am looking for some other solution (preferably xaml way one).

private void Button_Click(object sender, RoutedEventArgs e)
{
  this.myGrid.ColumnDefinitions[1].Width = GridLength.Auto;
  this.label1.Visibility = Visibility.Collapsed;
}

Answer 1

I added Xaml Binding as suggested by Rob like this:

<Grid.ColumnDefinitions>
  <ColumnDefinition Width="*" />
  <ColumnDefinition Width="{Binding MiddleColumnWidth}" />
  <ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>

<Label Grid.Row="0" Grid.Column="0">One</Label>
<Label Grid.Row="0" Grid.Column="1" Visibility="{Binding IsSecondLabelVisible}">Two</Label>
<Label Grid.Row="0" Grid.Column="2">Three</Label>

Code behind xaml:

private bool ShowOnlyTwoColumns;

private GridLength MiddleColumnWidth
{
  get
  {
    if (ShowOnlyTwoColumns)
      return GridLength.Auto; // Auto collapses the grid column when label is collapsed

    return new GridLength(1, GridUnitType.Star);
  }
}

private Visibility IsSecondLabelVisible
{
  get { return this.ShowOnlyTwoColumns ? Visibility.Collapsed : Visibility.Visible; }
}

Answer 2

The desired behaviour can be achieved using a UniformGrid.

Make sure to set the number of rows to 1.

<UniformGrid Rows="1">
    <Label>One</Label>
    <Label>Two</Label>
    <Label>Three</Label>
</UniformGrid>

The remaining elements are evenly spaced.

<UniformGrid Rows="1">
    <Label>One</Label>
    <Label Visibility="Collapsed">Two</Label>
    <Label>Three</Label>
</UniformGrid>

Answer 3

I ended up with an idea similar to h.m.i.13 answer. I created generic a converter that hides a column/row or displays it with a specific grid length value. The advantage is that it will work with more complex grids where not every row has a simple 1-star length.

public class BooleanToGridLengthConverter : IValueConverter
{
    private readonly static GridLength DefaultLength = new GridLength(0, GridUnitType.Pixel);

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is not bool booleanValue ||
            parameter is not string stringParameter)
        {
            return DefaultLength;
        }

        if (booleanValue && TryParseGridLength(stringParameter, out var gridLength))
        {
            return gridLength;
        }

        return DefaultLength;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }

    private static bool TryParseGridLength(string stringValue, out GridLength gridLength)
    {
        gridLength = DefaultLength;

        if (stringValue.Equals("Auto", StringComparison.OrdinalIgnoreCase))
        {
            gridLength = GridLength.Auto;
            return true;
        }

        if (stringValue.EndsWith("*"))
        {
            double starCount = 1;
            if (stringValue.Length > 1 && !double.TryParse(stringValue.AsSpan(0, stringValue.Length - 1), out starCount))
            {
                return false;
            }

            gridLength  = new GridLength(starCount, GridUnitType.Star);
            return true;
        }

        if (double.TryParse(stringValue, out var pixelValue))
        {
            gridLength = new GridLength(pixelValue, GridUnitType.Pixel);
            return true;
        }

        return false;
    }
}

And then the usage:

<Grid.ColumnDefinitions>
    <ColumnDefinition/>
    <ColumnDefinition Width="{Binding MyBooleanProperty, Converter={StaticResource BooleanToGridLength}, ConverterParameter=3*}"/>
</Grid.ColumnDefinitions>

Answer 4

I'm late, but I want to present my solution, in case it is useful to anyone.

I use this converter

public class BooleanToAutoOrStarGridLengthConverter : MarkupExtension, IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is bool isStar)
            return new GridLength(1, isStar ? GridUnitType.Star : GridUnitType.Auto);
        return new GridLength(0, GridUnitType.Star);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is GridLength gridLength && gridLength.GridUnitType == GridUnitType.Star)
            return true;
        return false;
    }

    public override object ProvideValue(IServiceProvider serviceProvider) => this;
} 

in XAML like this:

<Grid.ColumnDefinitions>
  <ColumnDefinition Width="*" />
  <ColumnDefinition Width="{Binding IsSecondLabelVisible, Converter={BooleanToAutoOrStarGridLengthConverter}}" />
  <ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>

<Label Grid.Row="0" Grid.Column="0">One</Label>
<Label Grid.Row="0" Grid.Column="1" Visibility="{Binding IsSecondLabelVisible}">Two</Label>
<Label Grid.Row="0" Grid.Column="2">Three</Label>