Property Based Content Filters
The UI can be customized to accept user inputs as filter criteria, and reduce the entire child list to a sub-list based on property values that contain that text. Each filter is 'attached' to a single metaproperty, and multiple filters can be applied at once.
 | When multiple filters are used at the same time, they are combined with "logic and". |
For performance/usability reasons, the result list is not immediately refreshed as one types in the text box. Instead, it only happens after the ReloadChildListCommand is triggered.
However, note that these content-based filters:
- Require a custom Child Area template name to work. This customizing will not work applied to the UBIKChildArea.
- Work directly on the Children.Items collection. While filters are active, anything derived from this collection (such as Children.Items.Count or custom datasources like ListCollectionView / sfDataSourceExt) will also be affected.
Contents
Usage
For simple text input, it is enough to create a text input control with a TwoWay relationship to the Children.Filter[x]. However, the TwoWay binding doesn't always work well with more advanced implementations, such as selection. In such cases, the alternative is to use the UpdatePropertyFiltersCommand to supply the filter criteria. Both approaches are described below.
Text Input
UWP
Text="{Binding Children.Filters[SomePropertyName], Mode=TwoWay, Converter={StaticResource FilterCriterionToValueConverter}}"
PlaceholderText="SomePropertyName" />
Xamarin
Placeholder="Filter by Name"
Text="{Binding Children.Filters[DESCR], Mode=TwoWay, Converter={StaticResource FilterCriterionToValue}}"/>
This is shown as a single text box. The two way binding on Text allows the entered text (case insensitive) to be used as the filter value on property "SomePropertyName" (case sensitive).
Selection
Selection is trickier to achieve than direct input, as often a metaproperty's actual value might differ from the text that is displayed for that value. Just think of integer-based statuses, or GUID properties.
UWP
x:Name="ComboBox"
PlaceholderText="{Binding Children.Filters[STATUSCOLOR].Value, FallbackValue='SELECT'}"
DisplayMemberPath="DisplayText"
SelectedValuePath="DisplayText"
SelectedValue="{Binding Children.Filters[STATUSCOLOR].Value}"
SelectedValueExt="{Binding Children.Filters[STATUSCOLOR].Value}"
ItemsSource="{Binding Children.Items[1].Properties.AllItems[STATUSCOLOR].MetaProperty.SelectiveList, Converter={StaticResource SelectiveListToItemsConverter}}">
<interactivity:Interaction.Behaviors>
<core:EventTriggerBehavior EventName="SelectionChanged">
<core:InvokeCommandAction Command="{Binding Children.UpdatePropertyFiltersCommand}">
<core:InvokeCommandAction.CommandParameter>
<controls:KeyValueList>
<controls:KeyValueParameter Key="ClearPropertyFilters" Value="false" />
<controls:KeyValueParameter Key="STATUSCOLOR" Value="{Binding SelectedItem.DisplayText, ElementName=ComboBox}" />
</controls:KeyValueList>
</core:InvokeCommandAction.CommandParameter>
</core:InvokeCommandAction>
</core:EventTriggerBehavior>
</interactivity:Interaction.Behaviors>
</controls:ComboBoxExt>
Note that several elements are required for this customization to work:
- SelectedValuePath informs the control of which property should be supplied to the command as a filter criteria. This should match what is supplied in your KeyValueParameter.
- DisplayMemberPath informs the control of which property should be visualized as the displaytext of your selection.
- PlaceholderText binds to the same value as your SelectedValueExt to display the current selected item. This is a workaround for a failure of the ComboBox control to correctly display an active selection when the control is rendered.
Xamarin
xmlns:classes="clr-namespace:UBIK.CPL.Classes;assembly=UBIK.CPL">
<ctrls:PickerExt
x:Name="Filter"
ItemsSource="{Binding Properties.AllItems[QUERY].LinkedLevel.Children.Items}"
ItemDisplayBinding="{Binding Header}"
SelectionChangedCommand="{Binding Children.UpdatePropertyFiltersCommand}"
SelectedValuePath="UID"
SelectedValue="{Binding Children.Filters[STA].Value, Mode=OneWay}">
<ctrls:PickerExt.SelectionChangedCommandParameter>
<classes:KeyValueList>
<classes:KeyValueParameter Key="ClearPropertyFilters" Value="false" />
<classes:KeyValueParameter Key="STA" Value="{Binding Path=SelectedItem.UID, Source={x:Reference Filter}}" />
</classes:KeyValueList>
</ctrls:PickerExt.SelectionChangedCommandParameter>
</ctrls:PickerExt>
The example above uses a custom ComboBox/Picker control to display a list of items. The chosen aspect of the of the selected object is then passed on as a part of the command parameter and later used as a filter criterion to filter for objects that have the same the string.
This approach makes use of the Children.UpdatePropertyFiltersCommand, which uses the following parameters:
- ClearPropertyFilters: Clear out all existing filters at the current level before executing the command. This is optional and defaults to false;
- All other parameters: KeyValue pairs used as filter criteria where the Keys are the names of the metaproperties by which you want to filter.
Evaluation Criteria
By default, the expression used for filtering is Content["PROPERTY_NAME"].DisplayValue.ToLower().Contains(FILTER_VALUE.ToLower())==true. In other words, it checks whether the specified filter value (as string) is contained in the display value of the property.
In more advanced scenarios where a different type of comparison is needed, the example (or more specifically the one KeyValueParameter) can be extended into the following, e.g. comparing whether the specified filter value is equal to the value of the property.
<classes:KeyValueParameter Key="STA" Value="{Binding Path=SelectedItem.UID, Source={x:Reference Filter}, Converter={StaticResource FilterValueToCriterion}, ConverterParameter=Content[\"\{0\}\"].Value.ToString().Equals(\"\{1\}\")\=\=true}" /> </source>
| """ and "\" are used for escaping the special characters in XAML and C# code respectively. "{0}" and "{1}" are placeholders and get replaced by the property name and the filter value. The end expression being executed in this example is Content["PROPERTY_NAME"].Value.ToString().Equals(FILTER_VALUE)==true |
UI Customizing
Update Child List
For performance/usability reasons, the result list is not immediately refreshed as one types in the text box. Instead, it only happens after the ReloadChildListCommand is triggered.
Filtered Indicator
You can also customize UI elements to indicate that filters are active.
UWP: The above border is shown when a filter is active.
