Step 4: Display Summaries

• Dec 30, 2021
• 3 minutes to read

This step describes how to display summaries:

• Process summaries in the virtual source.
• Display summaries in the GridControl.

Note

This tutorial uses the Issues Service as a sample data source.

Run Demo: Infinite Scrolling Source - Step 4 Run Demo: Paged Source - Step 4

Summary Types

The Issues Service allows you to obtain:

• The total count of rows.
• The last created object’s datetime.

C#

public class IssuesSummaries {   
    public int Count { get; private set; }
    public DateTime? LastCreated { get; private set; }
}

Display Summaries

1. Process summaries in the virtual source:

   • Create a task that uses the Issues Service‘s GetSummariesAsync method to get summaries from the data source.
   • Use the Summaries property to get the GridControl‘s summary items.
   • Create a GetTotalSummaries command.
   • Get a list of data source summaries that correspond to the GridControl‘s summary items. Assign the list to the Result property.
   • Bind the GetTotalSummaries command to the InfiniteAsyncSource.GetTotalSummariesCommand property.
   C#

   [Command]
   public void GetTotalSummaries(GetSummariesAsyncArgs args) {
       args.Result = GetTotalSummariesAsync(args);
   }
   static async Task<object[]> GetTotalSummariesAsync(GetSummariesAsyncArgs args) {
       var summaryValues = await IssuesService.GetSummariesAsync((IssueFilter)args.Filter);
       return args.Summaries.Select(x => {
           if(x.SummaryType == SummaryType.Count)
               return (object)summaryValues.Count;
           if(x.SummaryType == SummaryType.Max && x.PropertyName == "Created")
               return summaryValues.LastCreated;
           throw new InvalidOperationException();
       }).ToArray();
   }
   

   XAML

   <dxg:GridControl.ItemsSource>
       <dx:InfiniteAsyncSource ElementType="{x:Type local:IssueData}"
                               FetchRowsCommand="{Binding FetchIssuesCommand}"
                               GetUniqueValuesCommand="{Binding GetUniqueValuesCommand}"
                               GetTotalSummariesCommand="{Binding GetTotalSummariesCommand}"/>
   </dxg:GridControl.ItemsSource>
   

2. Set the DataViewBase.ShowFixedTotalSummary property to true to show the Fixed Summary Panel:

   XAML

   <dxg:GridControl.View>
       <dxg:TableView ShowFixedTotalSummary="True"/>
   </dxg:GridControl.View>
   

3. Specify the GridControl.TotalSummary property to display total summaries in the GridControl:

   XAML

   <dxg:GridControl.TotalSummary>
       <dxg:GridSummaryItem SummaryType="Count" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Max" FieldName="Created" 
                            DisplayFormat="{}Last created: {0}" Alignment="Right"/>
   </dxg:GridControl.TotalSummary>
   

Display Custom Summaries

In the example below, the Issues Service can calculate the Median and StdDev values:

C#

public class IssuesSummaries {
    // ...
    public double VotesMedian { get; private set; }
    public double VotesStdDev { get; private set; }
}

1. Process summaries in the virtual source:

   C#

   [Command]
   public void GetTotalSummaries(GetSummariesAsyncArgs args) {
       args.Result = GetTotalSummariesAsync(args);
   }
   static async Task<object[]> GetTotalSummariesAsync(GetSummariesAsyncArgs args) {
       var summaryValues = await IssuesService.GetSummariesAsync((IssueFilter)args.Filter);
       return args.Summaries.Select(x => {
           if (x.SummaryType == SummaryType.Count)
               return (object)summaryValues.Count;
           if (x.SummaryType == SummaryType.Max && x.PropertyName == "Created")
               return summaryValues.LastCreated;
   
           // Custom Summaries
           if (x.SummaryType == SummaryType.Custom && x.PropertyName == "Votes") {
               var tag = x.Tag as string;
               if (tag == "Median")
                   return summaryValues.VotesMedian;
               if (tag == "StdDev")
                   return summaryValues.VotesStdDev;
           }
           throw new InvalidOperationException();
       }).ToArray();
   } 
   

2. Display summaries in the GridControl:

   Xaml

   <dxg:GridControl.TotalSummary>
       <dxg:GridSummaryItem SummaryType="Count" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Max" FieldName="Created" 
                            DisplayFormat="{}Last created: {0}" Alignment="Right"/>
       <!-- Custom Summaries -->
       <dxg:GridSummaryItem SummaryType="Custom" Tag="StdDev" FieldName="Votes" 
                            DisplayFormat="{}Votes StdDev={0}" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Custom" Tag="Median" FieldName="Votes" 
                            DisplayFormat="{}Votes Median={0}" Alignment="Right"/>
   </dxg:GridControl.TotalSummary> 
   

Continue or Review

• Proceed to Step 5 - Enable Data Edit Operations.
• Review Step 3 - Enable Filter Operations.