Set DataContext for HeaderTemplate

Question

Is there a way to set a data context for a HeaderTemplate?

I want to add checkbox to the header and save it as setting of Column.

I've made the DataTemplate and set it to a column.HeaderTemplate property.

But I can't set object which will be used for use this setting. I see the HeaderText value only

Sreemon Premkumar Muthukrishnan · Answer

Hi basil,We are a little unclear about the information you have provided regarding how you are trying to use that checkbox. We suspect that you are expecting the checkbox to be displayed in the column header cell along with the header text. This can be achieved by defining the checkbox inside the DataTemplate and binding the content property. Please refer to the code snippet below: We have created the sample based on your requirement, please find it in the attachment. If we misunderstood your requirement, provide more information related to your query. It will be helpful for us to check on it and provide you the solution at the earliest.Regards, Sreemon Premkumar M.Attachment: WinUIDataGridCheckbox_9c4c513a.zip

basil · Answer

I attach a modified example. I create a new class, TableColumnDescription and set IsVisible property to true.

I have written a couple comments in code.

When you run the app, you'll see checkboxes are unchecked, but property of each column is set to true. Because I don't have a DataContext there.

Attachment: syncfusionexample_e254945f.zip

Vijayarasan Sivanandham · Answer

Basil, Solution 1: The class's data context isn't readily accessible within the DataTemplate. To overcome this, the ElementName binding mode in XAML can be employed alongside a named element. However, in your specific scenario, you're attempting to access a class that isn't accessible via the DataContext. It's important to note that direct access to a class beyond the DataContext's scope isn't feasible.Nevertheless, a solution is feasible. By crafting a ViewModel class that houses both your class's instance and the desired property for CheckBox binding, you can achieve your objective. This approach establishes a bridge between your class and the DataContext, enabling seamless interaction and binding. Refer to the below code snippet, XAML Code Snippet: C# Code Snippet: public class ViewModel { // Maintain the property in the view model to bind CheckBox public bool IsVisible { get { // return the value of the property from the TableCol return tableColumnDescriptor.IsVisible; } set { //Set the value to the property in the TableColumnDe tableColumnDescriptor.IsVisible = value; } } // Maintain the property for TableColumnDescriptor TableColumnDescriptor tableColumnDescriptor; public ViewModel() { // initialize the TableColumnDescriptor tableColumnDescriptor = new TableColumnDescriptor(); } } Solution 2: Alternatively, you can directly introduce the necessary property within the ViewModel and establish a binding connection with the CheckBox control. This method avoids the need to access the class which might not be directly available within the DataContext. By incorporating this property into the ViewModel, you ensure a smoother binding process and streamline the interaction with the CheckBox control. Refer to the below code snippet, XAML Code Snippet: C# Code Snippet: public class ViewModel { // Directly created property in the view model to bind CheckBox public bool IsChecked { get; set; } = true; } Find the modified sample demo in the attachment. If this post is helpful, please consider Accepting it as the solution so that other members can locate it more quickly. Attachment: ModifiedSample_95b8a4fa.zip

basil · Answer

I want to use each an element of Columns property as different DataContext for a grid header.

Please pay attention on my comment in the MainWindow.xaml.cs file (lines 25-32).

I want to have possibility to set DataContext as it is written on line 32.

I mean I can't set DataContext to GridHeaderCellControl through a GridTextColumn instance.

I can suppose you have something like this in your code where you render a Grid Column Header:

public class GridHeaderCellControl
{
    .....
    public void RenderColumnHeaderTemplate(string headerText)
    {
        DataTemplate template = this.HeaderTemplate;
        if (template != null)
        {
            var content = template.LoadContent() as FrameworkElement;
            if (content != null)
            {
                content.DataContext = headerText; // *
                ....
            }
        }
        ....
    }
}

* you set a text as the DataContext, but it would be better to add a new property to the GridTextColumn class and use it for the HeaderDataContext.

Vijayarasan Sivanandham · Answer

Basil,

Your requirement to add a new property to the GridTextColumn can be achieved by
creating the custom column. Refer to the below code snippet,

Code Snippet related to Custom column:

//Custom Column
  public class CustomGridTextColumn : GridTextColumn
  {
      //Create the Custom property based on your
  scenario
      public object
  DataContext
      {
         
  get { return GetValue(DataContextProperty); }
         
  set { SetValue(DataContextProperty, value); }
      }
   
      public static readonly
  DependencyProperty DataContextProperty =
         
  DependencyProperty.Register(
             
  "DataContext",
             
  typeof(object),
             
  typeof(CustomGridTextColumn),
             
  new PropertyMetadata(null)
         
  );
   
  }

Code Snippet related to Column define:

var
  column = new CustomGridTextColumn
  {
     
  MappingName = columnDescription.PropertyName,
     
  HeaderText = columnDescription.Header ??
  columnDescription.PropertyName,    
     
  HeaderTemplate = checkboxTemplate,
      // Set the DataContext of the column to the
  columnDescription object
      DataContext = columnDescriptor
  };

Find the modified sample in the attachment.Attachment: SfDataGridDemo_cf1faeec.zip

basil · Answer

Do you bind to Grid.IsVisible property?? It's not a solution.If I remove the ElementName property I get a binding error like thisAs you can see, the DataContext of the template is a reference to string, but not the CustomColumn.DataContext.Your solution is not a solution.

Sreemon Premkumar Muthukrishnan · Answer

Hi Basil,We are a bit unclear about your requirement. Could you please provide more information regarding your specific requirements? This will help us to check on it and provide you a better solution as soon as possible. We look forward to receiving the information you will provide.Regards,Sreemon Premkumar M.

basil · Answer

My task is the following:I have a set of columns descriptors (TableColumnDescriptor)Each of the descriptor has three properties: Header (for column header), Property (property of model to bind from) and IsVisible.I want to change the IsVisible property by clicking on the checkbox in the column header.For example, I open the app and check two checkboxes.  Then I click the button on the bottom of app. The EventHandler of Click event collects all IsVisible values and write result into the Output panel. And I expect to get the result like "False, True, True, False", because two checkboxes are selected.But I get "True, True, True, True" How can I set the DataContext for HeaderTemplate?I hope you help me.PS: I attached the changed app.Attachment: s3_285e8372.zip

Vijayarasan Sivanandham · Answer

Basil,

Your requirement to change the IsVisible property by clicking on the checkbox in the column header in SfDataGrid can be achieved by defining ViewModel (DataContext) inside Resources and you can bind ViewModel to Grid and CheckBox by using StaticResource binding as in the following code example.

XAML code snippet:

<Grid.Resources>

<local:ViewModel x:Key="viewModel" />

<local:DataContextConverter x:Key="dataContextConverter" />

<DataTemplate x:DataType="dataGrid:GridHeaderCellControl"

x:Key="CheckboxHeaderDataTemplate">

<CheckBox Content="{Binding PropertyName,Mode=TwoWay}"

IsChecked="{Binding IsVisible,Mode=TwoWay}"

DataContext="{Binding Converter={StaticResource dataContextConverter}, ConverterParameter={StaticResource viewModel}}" />

</DataTemplate>

</Grid.Resources>

C# code snippet related to setting the Grid's DataContext by accessing the ViewModel's resource key:

//Assign DataContext to the Grid

Root.DataContext = Root.Resources["viewModel"];

//Maintain the DataContext in common property to access in this class

_vm = Root.DataContext as ViewModel;

C# code snippet related to setting the DataContext of each column differently by using the converter to set DataContext:

public class DataContextConverter : IValueConverter

{

public object Convert(object value, Type targetType, object parameter, string language)

{

// Get the DataContext using the parameter

var viewModel = parameter as ViewModel;

if (viewModel != null)

{

// Get the TableColumnDescriptor for each column based on property name

var getTableColumnDescriptorColumn = viewModel.Columns.FirstOrDefault(x => x.PropertyName == value.ToString());

// Set the CheckBox DataContext as TableColumnDescriptor of specific column

return getTableColumnDescriptorColumn;

}

return value;

}

public object ConvertBack(object value, Type targetType, object parameter, string language)

{

return value;

}

Find the modified sample in the attachment.

If this post is helpful, please consider Accepting it as the solution so that other members can locate it more quickly.

Attachment: ModifiedSample_b6d136ea.zip

basil · Answer

Thank you, It is an unusual way to use viewModel.But if I create a viewModel through some ViewModelFactory or get it through DI?

Vijayarasan Sivanandham · Answer

Basil,In WinUI platform framework itself does not support the multi binding that’s why we suggested a solution in the previous update. However, you can achieve this by loading data initially through a converter and dynamic runtime changes using the Command feature within the CheckBox Control. This combination of techniques will allow you to attain the desired functionality. Refer to the below code snippet,XAML Code Snippet: C# code snippet related to Command: // Method to be executed when the CheckBoxCommand is executed private void CheckBoxAction(object parameter) { // Get the column from the Columns collection based on the parameter var getcolumn = Columns.FirstOrDefault(c => c.PropertyName == parameter.ToString()); // Change the IsVisible property of the column getcolumn.IsVisible = !getcolumn.IsVisible; // Your command logic here } C# code snippet related to converter: public class InitialDataConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, string language) { if (value != null) { // Get the ContentPresenter var contentPresenter = value as ContentPresenter; if (contentPresenter != null) { // Get the column name using the ContentPresenter DataContext var columnName = contentPresenter.DataContext; // Get the GridTextColumn using the ContentPresenter Parent var gridTextColumn = (contentPresenter.Parent as Grid)?.DataContext as GridTextColumn; if (gridTextColumn != null) { // Get the DataGrid using the GridTextColumn DataGrid property using reflection var dataGrid = (SfDataGrid)gridTextColumn.GetType().GetProperty("DataGrid", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(gridTextColumn); // Get the ViewModel using the DataGrid DataContext var viewModel = dataGrid?.DataContext as ViewModel; if (viewModel != null) { // Get the column using the ViewModel Columns property var getColumns = viewModel.Columns.FirstOrDefault(x => x.PropertyName == columnName.ToString()); // Return the column IsVisible property based different column return getColumns.IsVisible; } } } return value; } else { return value; } } public object ConvertBack(object value, Type targetType, object parameter, string language) { return value; } } Note: This is the final way to meet your requirements. There are no other ways to fulfill your requirements. Find the modified sample in the attachment. If this post is helpful, please consider Accepting it as the solution so that other members can locate it more quickly.Attachment: Modified_Sample_f3af6b5b.zip