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.NET and JavaScript UI Controls
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Apply Cell Value Templates Conditionally (xamDataPresenter)

Topic Overview

Purpose

This topic explains how you can conditionally supply display and edit templates for cells via properties exposed off a TemplateField.

Required background

The following topics are prerequisites to understanding this topic:

Topic Purpose

This topic introduces the xamDataGrid control and various elements, on which control is composed.

This topic explains the difference between Data Items and Data Records.

This topic describes how to define field layouts to specify which fields to display and to set properties related to those fields in the xamDataPresenter controls.

In this topic

This topic contains the following sections:

Template Selector Summary

Description

The data presenter controls support applying templates dynamically to a TemplateField for both displaying and editing a cell value. You have the ability to set "selectors" on a TemplateField which are used to provide the conditional logic for applying different templates based on the value being edited. The selector class should extend from the DataTemplateSelector class and implement the SelectTemplate method which returns a DataTemplate type.

The SelectTemplate method is called on the selector specified via the TemplateField’s DisplayTemplateSelector property in the following cases:

  • when each CellValuePresenter is created and displayed

  • after a CellValuePresenter exits edit mode

  • when the value of a cell changes while not in edit mode

The SelectTemplate method is called on the selector specified via the TemplateField’s EditTemplateSelector property in the following cases:

  • as a CellValuePresenter is entering editing mode

  • when the cell’s value changes while in edit mode

Note
Note

The SelectTemplate method of an editing template selector will be invoked repeatedly on each user typing when in edit mode. If your selector logic returns different template after the CellValuePresenter enters edit mode this will cause a focus loss and ending the editing mode. To prevent this you should save an instance of the first DataTemplate provided when entering edit mode (for example in the editor’s Tag property) and returns only this instance until the editing ends by user request. See the example code snippets below.

Tasks

The following table explains briefly the configurable aspects of the xamDataGrid control and maps them to the properties that configure them.

Tasks Details Property

Set selector to be used when a cell is not in edit mode

Set a selector class to be used to provide a template for cells that are not is edit mode for a specific TemplateField.

Note
Note

If the DisplayTemplate property is also set then this property is ignored.

DisplayTemplateSelector

Set selector to be used when a cell is in edit mode

Set a selector class to be used to provide a template for cells that are in edit mode for a specific TemplateField.

Note
Note

If the EditTemplate property is also set then this property is ignored. If neither the EditTemplate nor EditTemplateSelector properties are set then the DisplayTemplate or DisplayTemplateSelector properties will be used in edit mode as well.

EditTemplateSelector

Code snippet

The following code defines some display and edit templates:

In XAML:

…
<Page.Resources>
    <DataTemplate x:Key="displayTemplateRed">
        <TextBlock Text="{igEditor:TemplateEditorValueBinding}" Forground="Red" />
    </DataTemplate>
    <DataTemplate x:Key="displayTemplateGreen">
        <TextBlock Text="{igEditor:TemplateEditorValueBinding}" Forground="Green" />
    </DataTemplate>
    <DataTemplate x:Key="editTemplateRed">
        <TextBox Text="{igEditor:TemplateEditorValueBinding}" Background="Red" />
    </DataTemplate>
    <DataTemplate x:Key="editTemplateGreen">
        <TextBox Text="{igEditor:TemplateEditorValueBinding}" Background="Green" />
    </DataTemplate>
</Page.Resources>
…

The following code implements the display template selector:

In Visual Basic:

Public Class CustomDisplayTemplateSelector
  Inherits DataTemplateSelector
  Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) _
      As DataTemplate
    Dim dataTemplate As DataTemplate = Nothing
    Dim editor = TemplateEditor.GetEditor(container)
    ' clearing the Tag property which in this case is used
    ' to track the template returned in edit mode.
    editor.Tag = Nothing
    If item IsNot Nothing Then
      If CInt(item) > 10000 Then
        dataTemplate = TryCast(editor.FindResource("displayTemplateRed"), DataTemplate)
      Else
        dataTemplate = TryCast(editor.FindResource("displayTemplateGreen"), DataTemplate)
      End If
    End If
    If dataTemplate IsNot Nothing Then
      Return dataTemplate
    End If
    Return MyBase.SelectTemplate(item, container)
  End Function
End Class

In C#:

public class CustomDisplayTemplateSelector : DataTemplateSelector
{
  public override DataTemplate SelectTemplate(object item, DependencyObject container)
  {
    DataTemplate dataTemplate = null;
    var editor = TemplateEditor.GetEditor(container);
    // clearing the Tag property which in this case is used
    // to track the template returned in edit mode.
    editor.Tag = null;
    if (item != null)
    {
      if ((int)item > 10000)
      {
        dataTemplate = editor.FindResource("displayTemplateRed") as DataTemplate;
      }
      else
      {
        dataTemplate = editor.FindResource("displayTemplateGreen") as DataTemplate;
      }
    }
    if (dataTemplate != null) return dataTemplate;
    return base.SelectTemplate(item, container);
  }
}

The following code implements the edit template selector:

In Visual Basic:

Public Class CustomEditTemplateSelector
  Inherits DataTemplateSelector
  Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) _
      As DataTemplate
    Dim dataTemplate As DataTemplate = Nothing
    Dim editor = TemplateEditor.GetEditor(container)
    ' If the Tag property is set this means that an edit template was already
    ' returned and we need to return the same template to prevent the editor
    ' to exit edit mode.
    If TypeOf editor.Tag Is DataTemplate Then
      Return TryCast(editor.Tag, DataTemplate)
    End If
    If item IsNot Nothing Then
      If CInt(item) > 10000 Then
        dataTemplate = TryCast(editor.FindResource("editTemplateRed"), DataTemplate)
      Else
        dataTemplate = TryCast(editor.FindResource("editTemplateGreen"), DataTemplate)
      End If
    End If
    If dataTemplate IsNot Nothing Then
      editor.Tag = dataTemplate
      Return dataTemplate
    End If
    Return MyBase.SelectTemplate(item, container)
  End Function
End Class

In C#:

public class CustomEditTemplateSelector : DataTemplateSelector
{
  public override DataTemplate SelectTemplate(object item, DependencyObject container)
  {
    DataTemplate dataTemplate = null;
    var editor = TemplateEditor.GetEditor(container);
    // If the Tag property is set this means that an edit template was already
    // returned and we need to return the same template to prevent the editor
    // to exit edit mode.
    if (editor.Tag is DataTemplate)
        return editor.Tag as DataTemplate;
    if (item != null)
    {
      if ((int)item > 10000)
      {
        dataTemplate = editor.FindResource("editTemplateRed") as DataTemplate;
      }
      else
      {
        dataTemplate = editor.FindResource("editTemplateGreen") as DataTemplate;
      }
    }
    if (dataTemplate != null)
    {
        editor.Tag = dataTemplate;
        return dataTemplate;
    }
    return base.SelectTemplate(item, container);
  }
}

The following code adds the display and edit selectors to the page’s resources:

In XAML:

…
<Page.Resources>
    <localNameSpace:CustomDisplayTemplateSelector x:Key="Selector1" />
    <localNameSpace:CustomEditTemplateSelector x:Key="Selector2" />
</Page.Resources>
…

The following code sets the display and edit selectors to a template field:

In XAML:

<igDP:XamDataGrid>
    <igDP:XamDataGrid.FieldLayouts>
        …
        <igDP:TemplateField Name="BasePrice" Label="Price"
            DisplayTemplateSelector="{StaticResource Selector1}"
            EditTemplateSelector="{StaticResource Selector2}"
        />
        …
    </igDP:XamDataGrid.FieldLayouts>
</igDP:XamDataGrid>

Related Topic

The following topic provides additional information related to this topic.

Topic Purpose

This topic describes how to create a field with a custom display and edit template using a TemplateField in the xamDataPresenter controls.