Unbound Columns (TreeList)

If you need to display custom information in a TreeList column, you can create an unbound column. This column is not bound to a field in the underlying data source. You should populate this column with data manually, using the TreeListControl.CustomUnboundColumnData event.

To create an unbound column, do the following:

Create a TreeListColumn object.
Set the column's UnboundDataType property to the type of data this column is intended to display.
Set the column's FieldName property to a unique field name.
Add the column to the TreeListControl.Columns collection, using the Add or Insert method. You can also position the column with the TreeListColumn.VisibleIndex property.

Note that the control does not store or cache data for unbound columns. It invokes the CustomUnboundColumnData event, which you need to handle to specify data for unbound columns.

The CustomUnboundColumnData event fires in two cases:

When TreeList needs to display a cell value in an unbound column. In this case, the IsGettingData event parameter returns true. You need to assign a value to the Value event parameter.
When a user changes data in unbound columns' cells. In this case, the IsGettingData event parameter returns false. Read the Value event parameter and cache it manually in your storage for further use.

Example 1

The following example creates an unbound read-only Total column, and handles the CustomUnboundColumnData event to calculate column values based on values of other fields, according to the expression: Total=UnitPrice*Quantity. The event handler checks the IsGettingData event parameter, and retrieves values when this parameter is true.

xmlns:mxtl="https://schemas.eremexcontrols.net/avalonia/treelist"
xmlns:sys="clr-namespace:System;assembly=System.Runtime"
...
<mxtl:TreeListControl Grid.Column="5" Width="400" Name="treeList1" 
                      CustomUnboundColumnData="treeList1_CustomUnboundColumnData" >
    <mxtl:TreeListControl.Columns>
        <mxtl:TreeListColumn Name="colUnitPrice" FieldName="UnitPrice" 
         Header="Unit Price" Width="*"  />
        <mxtl:TreeListColumn Name="colQuantity" FieldName="Quantity" 
         Header="Quantity" Width="*"/>
        <mxtl:TreeListColumn Name="colTotal" FieldName="Total" 
         Header="Total" Width="*" ReadOnly="True" 
         UnboundDataType="{x:Type sys:Decimal}" />
    </mxtl:TreeListControl.Columns>
</mxtl:TreeListControl>

List<PurchaseRecord> list = new List<PurchaseRecord>();
list.Add(new PurchaseRecord() { UnitPrice = 1.3m, Quantity = 2 });
list.Add(new PurchaseRecord() { UnitPrice = 4m, Quantity = 1 });
list.Add(new PurchaseRecord() { UnitPrice = 10m, Quantity = 20 });
list.Add(new PurchaseRecord() { UnitPrice = 7m, Quantity = 12 });

treeList1.ItemsSource = list;

private void treeList1_CustomUnboundColumnData(object? sender, 
 TreeListUnboundColumnDataEventArgs e)
{
    if (e.IsGettingData && e.Column.FieldName == "Total")
    {
        PurchaseRecord rec = e.Node.Content as PurchaseRecord;
        if (rec != null)
        {
            e.Value = rec.Quantity * rec.UnitPrice;
        }
    }
}

public partial class PurchaseRecord : ObservableObject
{
    [ObservableProperty]
    decimal unitPrice;
    [ObservableProperty]
    int quantity;
}

Example 2

The following example shows how you can cache data entered by users in unbound columns. The example creates a Data column and handles the CustomUnboundColumnData event to supply data to the TreeList and save data typed by users.

treeList1.Columns.Add(new TreeListColumn() 
{ 
    FieldName = "UserData", UnboundDataType = typeof(string), Header = "Data" 
});
treeList1.CustomUnboundColumnData += treeList1_CustomUnboundColumnData;

Dictionary<int, string> cache = new Dictionary<int, string>();

private void treeList1_CustomUnboundColumnData(object? sender, 
 TreeListUnboundColumnDataEventArgs e)
{
    if (e.Column.FieldName != "UserData") return;
    if (e.IsGettingData)
    {
        if (cache.ContainsKey(e.Node.Id))
            e.Value = cache[e.Node.Id];
        else
            e.Value = cache[e.Node.Id] = "-empty-";
    }
    else
    {
        cache[e.Node.Id] = e.Value.ToString();
    }
}

Table of Contents

Unbound Columns (TreeList)

Example 1

Example 2