How to show the rendered HTML inside the ToolTip of the WPF DataGrid?

By default, WPF DataGrid (SfDataGrid) does not have built-in support to render HTML code and display it in the ToolTip. However, we can achieve this requirement by rendering the HTML using WPF RichTextBoxAdv (SfRichTextBoxAdv).

In this approach, load the HTML code into RichTextBoxAdv, render the HTML content, and then set RichTextBoxAdv as the ToolTip content inside the CellToolTipOpening event.

Step 1: Subscribe to the CellToolTipOpening Event of the DataGrid

Subscribe to the CellToolTipOpening event of DataGrid, and enable the ShowToolTip property for the desired column where the ToolTip should be displayed.

<syncfusion:SfDataGrid HorizontalAlignment="Center"  
                       x:Name="dataGrid"  
                       ItemsSource="{Binding Orders}" 
                       AutoGenerateColumns="False" 
                       CellToolTipOpening="OnCellToolTipOpening">
   <syncfusion:SfDataGrid.Columns>
         <syncfusion:GridTextColumn HeaderText="Customer ID" 
                                    MappingName="CustomerID" 
                                    ShowToolTip="True"/>
       <syncfusion:GridTextColumn HeaderText="Customer Name" 
                                  MappingName="CustomerName"/>
   </syncfusion:SfDataGrid.Columns>
</syncfusion:SfDataGrid> 

Step 2: Customize the ToolTip content to display as HTML content

In the event handler, retrieve the HTML code, convert it into a stream, and pass it to RichTextBoxAdv. Then, set RichTextBoxAdv as the ToolTip content of the DataGrid.

   SfRichTextBoxAdv richTextBoxAdv = new SfRichTextBoxAdv() { Width = 300, Height = 200, LayoutType = LayoutType.Continuous};

   private void OnCellToolTipOpening(object sender, GridCellToolTipOpeningEventArgs e)
   {
      if (e.Record != null && e.Record is OrderInfo)
      {
          string htmlContent = (e.Record as OrderInfo).HTMLCode;
          if (htmlContent != null)
          {
             Stream stream = new MemoryStream();
             byte[] bytes = Encoding.UTF8.GetBytes(htmlContent);
             if (bytes != null)
                stream.Write(bytes, 0, bytes.Length);
             stream.Position = 0;
             richTextBoxAdv.Load(stream, FormatType.Html);
             e.ToolTip.Content = richTextBoxAdv;
          }      
       }
    }

Take a moment to peruse the WPF DataGrid - ToolTip documentation where you can find about the ToolTip with code examples.