InfiniteAsyncSource.FetchRows Event

Allows you to fetch rows.

Namespace: DevExpress.Xpf.Data

Assembly: DevExpress.Xpf.Core.v20.1.dll

NuGet Packages: DevExpress.WindowsDesktop.Wpf.Core, DevExpress.Wpf.Core

Declaration

C#

public event EventHandler<FetchRowsAsyncEventArgs> FetchRows

VB.NET

Public Event FetchRows As EventHandler(Of FetchRowsAsyncEventArgs)

Event Data

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

Property	Description
AllowRetry	Gets or sets whether re-requesting data is allowed. Inherited from FetchRowsEventArgsBase.
Filter	Gets the GridControl filtering. Inherited from FetchEventArgsBase.
Keys	Gets keys that you passed to the ReloadRows(Object[]) method.
Result	Gets or sets the result of the fetch rows operation.
Skip	Gets the number of rows to skip in a returned result set. Inherited from FetchEventArgsBase.
SkipToken	Gets the skip token. Inherited from FetchEventArgsBase.
SortOrder	Gets the GridControl‘s sorting. Inherited from FetchEventArgsBase.
Take	Gets one of the following values: null when the grid fetches next portion of data (a user scrolls rows). the number of rows within and above the viewport that are reloaded when you call the RefreshRows method or users press F5. int.Max when you call the InfiniteAsyncSource.ReloadRows / PagedAsyncSource.ReloadRows method. Inherited from FetchRowsEventArgsBase.

Remarks

To fetch rows from the data source:

• Handle the FetchRows event.
• Obtain data.
• Create the FetchRowsResult class object and specify the FetchRowsAsyncEventArgs.Result property.

C#

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

The FetchRowsEventArgsBase.Take property returns the number of rows that should be reloaded. Use this property to allow the InfiniteAsyncSource to retain a selected row and scroll position after refresh. The PagedAsyncSource automatically retains a selected row and scroll position.

If data in your source are changed frequently, you can retain the same selected row after refresh. Specify the VirtualSourceBase.KeyProperty property to make a virtual source find the selected row by a specific field.

Related GitHub Examples

The following code snippets (auto-collected from DevExpress Examples) contain references to the FetchRows event.

Note

The algorithm used to collect these code examples remains a work in progress. Accordingly, the links and snippets below may produce inaccurate results. If you encounter an issue with code examples below, please use the feedback form on this page to report the issue.

C#

how-to-bind-to-iqueryable/CS/MainWindow.xaml.cs#L22

source.FetchRows += (o, e) => {
    e.Result = Task.Run(() => FetchRows(e));

how-to-use-skip-tokens-to-optimize-paging-EF/CS/MainWindow.xaml.cs#L21

source.FetchRows += (o, e) => {
    e.Result = Task.Run(() => FetchRows(e));

wpf-data-grid-bind-to-infiniteasyncsource/CS/MainWindow.xaml.cs#L22

source.FetchRows += (o, e) => {
    e.Result = FetchRowsAsync(e);

how-to-bind-to-odata/CS/MainWindow.xaml.cs#L20

source.FetchRows += (o, e) => {
    e.Result = Task.Run(() => FetchRows(e));

how-to-bind-to-custom-service-with-restrictions/CS/MainWindow.xaml.cs#L22

source.FetchRows += (o, e) => {
    e.Result = FetchRowsAsync(e);

VB.NET

how-to-use-skip-tokens-to-optimize-paging-EF/VB/MainWindow.xaml.vb#L21

AddHandler source.FetchRows, Sub(o, e)
    e.Result = Task.Run(Function() FetchRows(e))

wpf-data-grid-bind-to-infiniteasyncsource/VB/MainWindow.xaml.vb#L18

AddHandler Unloaded, Sub(o, e) source.Dispose()
AddHandler source.FetchRows, Sub(o, e) e.Result = FetchRowsAsync(e)
AddHandler source.GetUniqueValues, Sub(o, e)

how-to-bind-to-odata/VB/MainWindow.xaml.vb#L20

AddHandler source.FetchRows, Sub(o, e)
    e.Result = Task.Run(Function() FetchRows(e))

how-to-bind-to-custom-service-with-restrictions/VB/MainWindow.xaml.vb#L22

AddHandler source.FetchRows, Sub(o, e)
    e.Result = FetchRowsAsync(e)

How-to-use-AutoSuggestEdit-with-InfiniteAsyncSource/VB/MainWindow.xaml.vb#L54

Dim source = New InfiniteAsyncSource() With {.ElementType = GetType(SCIssuesDemo)}
AddHandler source.FetchRows, Sub(o, e) e.Result = Task.Run(Function() FetchRows(e))
autoSuggestEdit.ItemsSource = source