Question

I have a DataGrid with many columns.

I want Width="Auto" with scrollbar showing everything if window narrower than all columns. If window wider I want columns to span empty space so there is no dead space.

Basically I want the column minimum width to fully fit contents or header. And expand to larger if window wider.

Answer 1

In XAML set DataGrid ColumnWidth="Auto"

In UserControl constructor add

dataGrid.Loaded += (s, e) => { // Column widths
    dataGrid.Columns.AsParallel().ForEach(column => {
        column.MinWidth = column.ActualWidth;
        column.Width = new DataGridLength(1, DataGridLengthUnitType.Star);
    });
};

Using this with a custom DataGrid and works great.