Contextfilter for DataGrid

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Update

I updated the filter control to cover some more scenarios. The filter now works when the data grid column is bound to sub properties like this:

<datagridcheckboxcolumn binding="{Binding Path=Character.Reliable}" header="Is reliable">

In my last project I also bound data grid columns to dictionary values. Now, these bindings are supported, too:

<datagridtextcolumn binding="{Binding Path=StringDictionary[Favorite name]}" header="Favorite name">

Furthermore, I added two filter related events to the filter control:

• FilterTurnedOn - Raised after a filter was applied
• FilterTurnedOff - Raised after the filter was removed

I use these events in the updated demo project to display the binding of the last filter action.

Introduction

You still remember the plain old Access GUI? Believe it or not, our development team still runs Access based apps. But as time advances, even we are going to feed them with modern desktop technology including animations, background threading and all that stuff to make users happy.

Unfortunately, the path to complete happiness is tempered by the missing filter in the WPF standard datagrid, which is a real shame, because the WPF infrastructure includes everything needed to implement this feature. 

This is why I created an Access like custom filter control which opens in a context menu like when the user right clicks the mouse button. 

Here is how it looks like if it opens on a datatime column:  

Selecting one of the possible filter operations in the list executes the filter on the underlying collection view.   

Features 

The filter control is sensitive to the property type the data column is bound and to the underlying column type.

If the datacolumn is bound to an enum or the column type is a DataGridCombobox column, the filter control offers a combobox to you choose the filter value. Custom types can be filtered as well if they are bound to a combobox column. Otherwise you get a textbox with disabled filter criteria. 

If the datacolumn is bound to simple value type like Int or to a string, a TextBox will be shown.

In this case you also get additional filter options like "Contains" and "DoesNotContain". If the datacolumn is bound to an int or another number type, you get this. 

The filter criterias are disabled, because I entered an invalid number into the textbox. The same goes for invalid dates and other input, thanks to a validation on keystroke.

Next the datacolumn is bound to a boolean. 

If the underlying boolean is nullable, the checkbox is in triple state, allowing you to filter for null values as well. Filtering nullable values is supported for other value types as well. 

Filter description and removing the filter   

After the filter is applied, the DataGrid header will show a filter icon. Hoovering over the icon displays the active filter criteria. 

Of course, you can sequentially filter  on different columns and multiple times on the same column. Every new filter action acts as an additional criteria the data must comply with to be displayed in the datagrid. 

After the first filter condition is applied, the "Remove filter" button is enabled. Pressing this button returns the unfiltered data set and returns the column header back to normal state.  

Using the filter control in you application  

Additionally to having a working filter, the second objective was to integrate the control as easily as possible into your application. Following steps need to be done: 

1. Add a reference to the DataGridContextMenuFilter DLL
2. Set the ContextMenu property of the DataGridCell to the DataGridContextMenuFilter  to make the filter control appear  when the user right clicks on any cell to add a new filter or to remove all filter settings 
3. Set the ContextMenu property of the DataGridColumnHeader to the DataGridContextMenuFilter control to make the filter control appear when the user right clicks on any header of the data grid. This is usefull to remove the filter in case you filtered all rows away. 

    <Window.Resources>

        <fc:FilterContextMenu x:Key="FilterControl" />

        <Style TargetType="DataGridColumnHeader">
            <Setter Property="ContextMenu" Value="{StaticResource FilterControl}" />
        </Style>

        <Style TargetType="DataGridCell">
            <Setter Property="ContextMenu" Value="{StaticResource FilterControl}" />
        </Style>

    </Window.Resources> 

Implementation details

The basic structure

The filter control is a custom control (as opposed to a user control) deriving from the context menu control, enabling us to assign the filter control to the context menu property of the datagrid cell and getting the desired pop up behavior for free.

As usual, this custom control consists of two parts:

The code file of the class containing (dependency) properties and behavior:

Namespace FilterControls
 
    Partial Public Class FilterContextMenu
        Inherits ContextMenu

	' Definition of properties and behaviour

    End Class
End Namespace

The Generic.XAML file (in this case only one) for its look:

<resourcedictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:cv="clr-namespace:DataGridContextMenuFilter.Converter" xmlns:local="clr-namespace:DataGridContextMenuFilter.FilterControls">
 
    <cv:invaliddatetonullconverter x:key="InvalidDateToNullConverter">
    <cv:invalidbooleantonullconverter x:key="InvalidBooleanToNullConverter">
 
    <style targettype="{x:Type local:FilterContextMenu}">
	
    <!—Definition of control elements including binding, etc.  -->

    </style>
</cv:invalidbooleantonullconverter></cv:invaliddatetonullconverter>&nbsp;</resourcedictionary> 

<cv:InvalidDateToNullConverter x:Key="InvalidDateToNullConverter" />
<cv:InvalidBooleanToNullConverter x:Key="InvalidBooleanToNullConverter" />

Public Overrides Sub OnApplyTemplate()
	MyBase.OnApplyTemplate()

' Creating references to controls defined in the Generic.XAML file

' Register some event handlers 
 
End Sub

Protected Overrides Sub OnOpened(e As System.Windows.RoutedEventArgs)
	MyBase.OnOpened(e)

 ' Determine the DataGridCell, the DataGridRow, the DataGridColumn and the DataGrid on which filtering occurs

 ' Based on this information set the filter relevant properties described above (FilterSource, CriteriaValue, CriteriaProperty)

 ' Determine visibility of criteria value and other controls

 ' Update list of allowed compare operations 

End Sub

Public Class Filter
        ' Some filter relevant properties
	' The “Filter” method it-self
End Class

Public Class FilterGroup

        ' A list containing all filters
	Private _FilterList As List(Of Filter)

        ' Execution of all filters
        Private Function ApplyFilter(o As Object) As Boolean
            For Each f In _FilterList
                If Not f.FilterLogic.Invoke(o) Then
                    Return False
                End If
            Next
 
            Return True
        End Function

	' Other stuff not relevant for understanding
End Class