DataSource.FetchTimeRegions Event

Allows you to load time regions only for the specified date range.

Namespace: DevExpress.Xpf.Scheduling

Assembly: DevExpress.Xpf.Scheduling.v23.2.dll

NuGet Package: DevExpress.Wpf.Scheduling

Declaration

C#

public event FetchDataEventHandler FetchTimeRegions

VB.NET

Public Event FetchTimeRegions As FetchDataEventHandler

Event Data

The FetchTimeRegions event's data class is FetchDataEventArgs. The following properties provide information specific to this event:

Property	Description
AsyncResult	Gets or sets a task that allows you to fetch data asynchronously in the SchedulerControl.
CancellationToken	Gets an object that notifies that the current data load has been cancelled during the asynchronous data fetch. The CancellationToken property is used when the RefreshData() method is invoked.
Ids	Returns the identifiers of scheduler items that have been reloaded by the ReloadAppointments/ReloadTimeRegions methods.
Interval	Returns the time range for which to fetch the scheduler items.
Result	Specifies the list of scheduler items to load from the data source.

The event data class exposes the following methods:

Method	Description
GetFetchExpression<T>()	Generates an expression that you can use to obtain appointments from the data source.
IsVisibleInterval()	Determines whether a specified interval is visible in the SchedulerControl at the current moment during the asynchronous data load.

Remarks

Specify TimeRegionMappings.QueryStart and TimeRegionMappings.QueryEnd mappings to handle the FetchTimeRegions event.

These mappings allow you to calculate the correct interval that is used in a SELECT query when you handle the FetchTimeRegions event. The use of the TimeRegionMappings.Start and TimeRegionMappings.End properties is not recommended in this scenario because such an interval may not include time region patterns and the corresponding exceptions.

The example below illustrates how to fetch time regions from a DbContext source. The FetchMode property is set to Bound.

C#

public class SchedulingDataContext : DbContext {
    public SchedulingDataContext() : base(CreateConnection(), true) { }
    static DbConnection CreateConnection() {
        //...
    }
    public DbSet<TimeRegionEntity> TimeRegionEntities { get; set; }

    //...
}
private void dataSource_FetchTimeRegions(object sender, DevExpress.Xpf.Scheduling.FetchDataEventArgs e) {
    using (var dbContext = new SchedulingDataContext()) {
        e.AsyncResult = dbContext.TimeRegionEntities
            .Where(x => x.QueryStart <= e.Interval.End
                && x.QueryEnd >= e.Interval.Start)
            .ToArrayAsync();
    }
}

VB.NET

 Public Class SchedulingDataContext
    Inherits DbContext

    Public Sub New()
        MyBase.New(CreateConnection(), True)
    End Sub
    Private Shared Function CreateConnection() As DbConnection
        '...
    End Function
    Public Property TimeRegionEntities() As DbSet(Of TimeRegionEntity)

    '...
End Class
Private Sub dataSource_FetchTimeRegions(ByVal sender As Object, ByVal e As DevExpress.Xpf.Scheduling.FetchDataEventArgs)
    Using dbContext = New SchedulingDataContext()
        Dim res = dbContext.AppointmentEntities.Where(args.GetFetchExpression(Of AppointmentEntity)())
        args.AsyncResult = QueryableExtensions.ToArrayAsync(Of Object)(res)
    End Using
End Sub

The FetchRange property specifies the time interval for which to fetch the time regions. FetchTimeRegion loads items for the SchedulerControl.VisibleIntervals extended up to the FetchRange.

Refer to this topic for more information: Load Data on Demand.