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c#wpfxamldata-bindingdatagrid

How do I bind a WPF DataGrid to a variable number of columns?


My WPF application generates sets of data which may have a different number of columns each time. Included in the output is a description of each column that will be used to apply formatting. A simplified version of the output might be something like:

class Data
{
    IList<ColumnDescription> ColumnDescriptions { get; set; }
    string[][] Rows { get; set; }
}

This class is set as the DataContext on a WPF DataGrid but I actually create the columns programmatically:

for (int i = 0; i < data.ColumnDescriptions.Count; i++)
{
    dataGrid.Columns.Add(new DataGridTextColumn
    {
        Header = data.ColumnDescriptions[i].Name,
        Binding = new Binding(string.Format("[{0}]", i))
    });
}

Is there any way to replace this code with data bindings in the XAML file instead?


Solution

  • Here's a workaround for Binding Columns in the DataGrid. Since the Columns property is ReadOnly, like everyone noticed, I made an Attached Property called BindableColumns which updates the Columns in the DataGrid everytime the collection changes through the CollectionChanged event.

    If we have this Collection of DataGridColumn's

    public ObservableCollection<DataGridColumn> ColumnCollection
    {
        get;
        private set;
    }
    

    Then we can bind BindableColumns to the ColumnCollection like this

    <DataGrid Name="dataGrid"
              local:DataGridColumnsBehavior.BindableColumns="{Binding ColumnCollection}"
              AutoGenerateColumns="False"
              ...>
    

    The Attached Property BindableColumns

    public class DataGridColumnsBehavior
    {
        public static readonly DependencyProperty BindableColumnsProperty =
            DependencyProperty.RegisterAttached("BindableColumns",
                                                typeof(ObservableCollection<DataGridColumn>),
                                                typeof(DataGridColumnsBehavior),
                                                new UIPropertyMetadata(null, BindableColumnsPropertyChanged));
        private static void BindableColumnsPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
        {
            DataGrid dataGrid = source as DataGrid;
            ObservableCollection<DataGridColumn> columns = e.NewValue as ObservableCollection<DataGridColumn>;
            dataGrid.Columns.Clear();
            if (columns == null)
            {
                return;
            }
            foreach (DataGridColumn column in columns)
            {
                dataGrid.Columns.Add(column);
            }
            columns.CollectionChanged += (sender, e2) =>
            {
                NotifyCollectionChangedEventArgs ne = e2 as NotifyCollectionChangedEventArgs;
                if (ne.Action == NotifyCollectionChangedAction.Reset)
                {
                    dataGrid.Columns.Clear();
                    foreach (DataGridColumn column in ne.NewItems)
                    {
                        dataGrid.Columns.Add(column);
                    }
                }
                else if (ne.Action == NotifyCollectionChangedAction.Add)
                {
                    foreach (DataGridColumn column in ne.NewItems)
                    {
                        dataGrid.Columns.Add(column);
                    }
                }
                else if (ne.Action == NotifyCollectionChangedAction.Move)
                {
                    dataGrid.Columns.Move(ne.OldStartingIndex, ne.NewStartingIndex);
                }
                else if (ne.Action == NotifyCollectionChangedAction.Remove)
                {
                    foreach (DataGridColumn column in ne.OldItems)
                    {
                        dataGrid.Columns.Remove(column);
                    }
                }
                else if (ne.Action == NotifyCollectionChangedAction.Replace)
                {
                    dataGrid.Columns[ne.NewStartingIndex] = ne.NewItems[0] as DataGridColumn;
                }
            };
        }
        public static void SetBindableColumns(DependencyObject element, ObservableCollection<DataGridColumn> value)
        {
            element.SetValue(BindableColumnsProperty, value);
        }
        public static ObservableCollection<DataGridColumn> GetBindableColumns(DependencyObject element)
        {
            return (ObservableCollection<DataGridColumn>)element.GetValue(BindableColumnsProperty);
        }
    }