Step 3: Enable Filtering

• Dec 26, 2018
• 2 minutes to read

In this step, you enable the filtering functionality in the GridControl bound to a virtual source.

Overview

The Issues Service can fetch rows:

• With a specified Priority.
• Over a period of time (between CreatedFrom and CreatedTo).
• With a maximum number of Votes.

C#

public class IssueFilter {  
    public Priority? Priority { get; private set; }
    public DateTime? CreatedFrom { get; private set; }
    public DateTime? CreatedTo { get; private set; }
    public int? MinVotes { get; private set; }
}

In Step 1: Fetch Data and Enable Scrolling, you have fetched rows without filtering:

C#

public MainPage() {
    // ... 
    source.FetchRows += (o, e) => {
        e.Result = FetchRowsAsync(e);
    };
}
static async Task<FetchRowsResult> FetchRowsAsync(FetchRowsAsyncEventArgs e) {
    IssueFilter filter = MakeIssueFilter(e.Filter);
    const int pageSize = 30;
    var issues = await IssuesService.GetIssuesAsync(
        page: e.Skip / pageSize,
        pageSize: pageSize,
        sortOrder: IssueSortOrder.Default,
        filter: filter);
    return new FetchRowsResult(issues, hasMoreRows: issues.Length == pageSize);
}
static IssueFilter MakeIssueFilter(CriteriaOperator filter) {
    return null;
}

To Enable Filtering

1. Implement filtering in the virtual source:

   • Get the GridControl‘s filtering using the DevExpress.Data.FetchEventArgsBase.Filter property.
   • Parse filtering and return a filter. The DevExpress.Data.InfiniteAsyncSource.FetchRows event handler takes into account this filter when fetching rows.
   C#

       static IssueFilter MakeIssueFilter(CriteriaOperator filter) {
           return filter.Match(
               binary: (propertyName, value, type) => {
                   if (propertyName == "Priority" && type == BinaryOperatorType.Equal)
                       return new IssueFilter(priority: (Priority)value);
                   if (propertyName == "Created") {
                       if (type == BinaryOperatorType.GreaterOrEqual)
                           return new IssueFilter(createdFrom: (DateTime)value);
                       if (type == BinaryOperatorType.Less)
                           return new IssueFilter(createdTo: (DateTime)value);
                   }
                   throw new InvalidOperationException();
               },
              and: filters => {
                  return new IssueFilter(
                      createdFrom: filters.Select(x => x.CreatedFrom).SingleOrDefault(x => x != null),
                      createdTo: filters.Select(x => x.CreatedTo).SingleOrDefault(x => x != null),
                      minVotes: filters.Select(x => x.MinVotes).SingleOrDefault(x => x != null),
                      priority: filters.Select(x => x.Priority).SingleOrDefault(x => x != null)
                  );
              },
              @null: default(IssueFilter)
          );
       }
   

   Tip

   The code sample above uses the DevExpress.Data.FilterCriteriaMatchHelper.Match method, which allows parsing filter criteria that the GridControl creates.

2. Get a list of priorities to show them in the Priority column’s drop-down filter:

   • Handle the DevExpress.Data.InfiniteAsyncSource.GetUniqueValues event.
   • Get a list of priorities and specify the DevExpress.Data.GetUniqueValuesAsyncEventArgs.Result property.
   C#

           source.GetUniqueValues += (o, e) => {
               if (e.PropertyName == "Priority") {
                   var values = Enum.GetValues(typeof(Priority)).Cast<object>().ToArray();
                   e.Result = Task.FromResult(values);
               }
               else if (e.PropertyName != "Created") {
                   throw new InvalidOperationException();
               }
           };
   

   Tip

   Your service or database may have a special method to get unique values.

3. Allow filtering in the GridControl by the Priority and Created columns values:

   XAML

           <Grid:GridDateColumn FieldName="Created" AllowSorting="True" AllowColumnFiltering="True" FilterPopupMode="DateSmart"/>
           <Grid:GridTextColumn FieldName="Priority" AllowColumnFiltering="True" />