Increase columns width in Silverlight DataGrid to fill whole DG width

Building on Henrik P's answer, this solution simply straightens out the bug with Width='*' so that you can set any column to be proportional like you can on a grid:

    private void DgSQLDataSizeChanged(object sender, SizeChangedEventArgs e)
    {
        var myDataGrid = (DataGrid)sender;

        // Do not change column size if Visibility State Changed
        if (myDataGrid.RenderSize.Width == 0) return;

        double totalActualWidthOfNonStarColumns = myDataGrid.Columns.Sum(
            c => c.Width.IsStar ? 0 : c.ActualWidth);

        double totalDesiredWidthOfStarColumns = 
            myDataGrid.Columns.Sum(c => c.Width.IsStar ? c.Width.Value : 0);

        if ( totalDesiredWidthOfStarColumns == 0 ) 
            return;  // No star columns

        // Space available to fill ( -18 Standard vScrollbar)
        double spaceAvailable = (myDataGrid.RenderSize.Width - 18) - totalActualWidthOfNonStarColumns;

        double inIncrementsOf = spaceAvailable/totalDesiredWidthOfStarColumns;

        foreach (var column in myDataGrid.Columns)
        {
            if ( !column.Width.IsStar ) continue;

            var width = inIncrementsOf * column.Width.Value;
            column.Width = new DataGridLength(width, DataGridLengthUnitType.Star);
        }
    }

I liked Henrik's answer but needed two columns to fill the extra space, like a grid.

Tested only in WPF, not in Silverlight:

I set up in WPF 3.5 SP1 and it works perfect, no guaranties about Silverlight, but if it works it's indeed charming.

<data:DataGridTextColumn Header="Time" Binding="{Binding}" Width="*" />

Solution:

    void dg_sql_data_SizeChanged(object sender, SizeChangedEventArgs e)
    {
        DataGrid myDataGrid = (DataGrid)sender;
        // Do not change column size if Visibility State Changed
        if (myDataGrid.RenderSize.Width != 0)
        {
            double all_columns_sizes = 0.0;
            foreach (DataGridColumn dg_c in myDataGrid.Columns)
            {
                all_columns_sizes += dg_c.ActualWidth;
            }
            // Space available to fill ( -18 Standard vScrollbar)
            double space_available = (myDataGrid.RenderSize.Width - 18) - all_columns_sizes;
            foreach (DataGridColumn dg_c in myDataGrid.Columns)
            {
                dg_c.Width = new DataGridLength(dg_c.ActualWidth + (space_available / myDataGrid.Columns.Count));
            }
        }
    }

I have created an attached property for the DataGrid that lets you do this in XAML:

<UserControl 
    xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  
    x:Class="GridProperties.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:gp="clr-namespace:GridProperties">
<Grid x:Name="LayoutRoot" Background="White">
    <data:DataGrid gp:GridEx.StarColumn="2">
        <data:DataGrid.Columns>
            <data:DataGridTextColumn Header="Column 1"/>
            <data:DataGridTextColumn Header="Column 2"/>
            <data:DataGridTextColumn Header="Column 3"/>
        </data:DataGrid.Columns>
    </data:DataGrid>
</Grid>
</UserControl>