AsyncItemsSourceProvider Class

A data provider that supplies suggestions for the AutoCompleteEdit in async mode.

Namespace: DevExpress.Maui.Editors

Assembly: DevExpress.Maui.Editors.dll

NuGet Package: DevExpress.Maui.Editors

Declaration

public class AsyncItemsSourceProvider :
    ItemsSourceProviderBase

Remarks

Follow the steps below to supply items to the editor in asynchronous mode:

• Attach the AsyncItemsSourceProvider to the editor and handle its ItemsRequested event.
• Use the RequestAsync or Request event argument to specify the method that returns items. The provider assigns the returned collection to the ItemsSource property.
• Use the Text event argument to obtain the text entered in the edit box and pass it to the specified method.

You can also specify the following options:

• RequestDelay – the time that should elapse after the text is changed and the request is called. Use this parameter to reduce the number of requests as a user types.
• CharacterCountThreshold – the number of entered characters after which the provider starts to make requests. For example, the provider can make requests only if a user enters at least three characters.

The provider cancels the previous request if a new request is submitted. You can use the CancellationToken event argument to cancel the previous request.

XAML

<dxe:AutoCompleteEdit.ItemsSourceProvider>
    <dxe:AsyncItemsSourceProvider
        CharacterCountThreshold="1"
        RequestDelay="500"
        ItemsRequested="OnAsyncItemsSourceProviderItemsRequested"/>
</dxe:AutoCompleteEdit.ItemsSourceProvider>

C#

void OnAsyncItemsSourceProviderItemsRequested(object sender, ItemsRequestEventArgs e) {
    e.RequestAsync = async () => await Task.Delay(3000).ContinueWith(task => this.employees.Where(employee => employee.FullName.Contains(e.Text)));
}

Examples

Populate an AutoCompleteEdit with Items

The example below uses the AsyncItemsSourceProvider to supply suggestions for the AutoCompleteEdit.

XAML

<dxe:AutoCompleteEdit LabelText="State"
                      PlaceholderText="Type here to search..."
                      VerticalOptions="Center"
                      Margin="16,0">
    <dxe:AutoCompleteEdit.ItemsSourceProvider>
        <dxe:AsyncItemsSourceProvider ItemsRequested="OnDelegateRequested" />
    </dxe:AutoCompleteEdit.ItemsSourceProvider>
</dxe:AutoCompleteEdit>

C#

using System.Collections.Generic;
using System.ComponentModel;
using Microsoft.Maui.Controls;

namespace AutoCompleteEditExample {
    public partial class MainPage : ContentPage {
        public MainPage() {
            InitializeComponent();
            States = new List<string>();
            States.AddRange(new string[] { "California", "Colorado", "Connecticut" /*...*/ });
        }
        public List<string> States { get; }
        void OnDelegateRequested(object sender, ItemsRequestEventArgs e) {
            e.Request = () => {
                return States.Where(i => i.StartsWith(e.Text, StringComparison.CurrentCultureIgnoreCase)).ToList();
            };
        }
    }
}

Populate an AutoCompleteColumn with Items

The example below uses the AsyncItemsSourceProvider to supply items for the AutoCompleteColumn:

XAML

<dxg:DataGridView ItemsSource="{Binding Path=Employees}">
    <dxg:DataGridView.Columns>
        <dxg:AutoCompleteColumn FieldName="JobTitle">
            <dxg:AutoCompleteColumn.ItemsSourceProvider>
                <dxe:AsyncItemsSourceProvider ItemsRequested="ItemsRequested"
                                              RequestDelay="500"
                                              CharacterCountThreshold="2"/>
            </dxg:AutoCompleteColumn.ItemsSourceProvider>                
        </dxg:AutoCompleteColumn>
    </dxg:DataGridView.Columns>
</dxg:DataGridView>

C#

using System.Collections.Generic;
using System.ComponentModel;
using Microsoft.Maui.Controls;

namespace DemoCenter.Forms.Views {
    public partial class FirstLookView : ContentPage {
        public FirstLookView() {
            InitializeComponent();
            BindingContext = new EmployeesRepository();
        }

        private void ItemsRequested(object sender, ItemsRequestEventArgs e) {
            EmployeesRepository employeesRepository = BindingContext as EmployeesRepository;
            e.Request = () => {
                return employeesRepository.JobTitles.Where(i => i.StartsWith(e.Text, StringComparison.CurrentCultureIgnoreCase)).ToList();
            };
        }
    }
    public class EmployeesRepository {
        public IList<Employee> Employees { get; set; }
        public IList<string> JobTitles { get; set; }
    }
    public class Employee {
        public string JobTitle { get; set; }
    }
}

Implements

INotifyPropertyChanged

Inheritance

Object

BindableObject

ItemsSourceProviderBase

AsyncItemsSourceProvider