WPF - expose binding methods for inherited column

Question

A reoccurring issue I have is needing to create enhanced text columns for datagrids. By that I mean columns that act just like normal text columns, but with an additional graphic or feature, like an image displayed next to the text. So I'm using template columns, but apparently this means having to "start from scratch" in generating a lot of the features expected of a normal text column, such as the textbox editing template:

<DataGridTemplateColumn.CellEditingTemplate>
         <DataTemplate>
              <TextBox 
                   FocusManager.FocusedElement="{Binding RelativeSource={RelativeSource Self}}" 
                    Text="{Binding Path=[binded text], Mode=TwoWay, UpdateSourceTrigger=LostFocus}"/>

I want to define a column that's inherited from DataGridTemplateColumn, then dump all this code into it, so I can reuse these columns with any datagrid I wish. But as shown above, I can't declare the binding in the class definition because that obviously depends upon usage.

How can I define an inherited datagrid column that makes use of child controls (specifically the cell editing textbox in this case), but still allows binding to be set for these controls when the column has been declared with xaml inside some actual datagrid?

So far I've tried to expose a method to do this, but it's not working:

Public Class MyTextColumn
Inherits DataGridTemplateColumn
....
Public Property EditorBinding As String
    Get....
    Set(value As String)
        Dim b As New Binding(value)
        b.Mode = BindingMode.TwoWay
        b.UpdateSourceTrigger = UpdateSourceTrigger.LostFocus
        Dim tb = DirectCast(Me.CellEditingTemplate.LoadContent, TextBox)
        tb.SetBinding(TextBox.TextProperty, b)
    End Set
End Property

Not working, my best guess is I'm not setting the Binding.Source, but I have no idea what I should be setting it to. It's getting pretty frustrating.

Answer 1

So if I understand you correctly, you want to be able to bind the text property of the TextBox to something on the parent control which will hold this child control of yours. You can't do that using the normal property (I'm guessing you got the "Can't bind because it's not the dependency property" exception or something similar).

This is how I usually do it without any problems. First you need to define a dependency property in the code behind. This should show you how to do it in the VB.net (I really really suck at VB.net so I won't pretend to give you any advice on that). Check the first example in VB.net. What you need to change first is from Boolean to String, you will also probably want to change the property name. Be careful to leave the "Property" part of the name where it stands in the example. GetType(MyCode) should be changed to the name of the class where you are implementing the dependency property (the name of your MyTextColumn class)

In the MyTextColumn xaml, it should look something like this:

<DataGridTemplateColumn.CellEditingTemplate>
         <DataTemplate>
              <TextBox 
                   FocusManager.FocusedElement="{Binding RelativeSource={RelativeSource Self}}" 
                    Text="{Binding Path=IsSpinning, RelativeSource={RelativeSource AncestorType=DataGridTemplateColumn}, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"/>

I've put the original property name IsSpinning, you should put there your chosen name. Also, you might have to fix the relative source if the base class is not DataGridTemplateColumn. This should pick up anything comming to your custom control.

The final step is to use your control:

<controls:MyTextColumn IsSpinning="{binding PropName}"/>

You basically bind it to whatever string you want. Feel free to write up any problems that you might have with my explanation or code and I'll fix my answer accordingly.