如何从视图模型中的构造函数调用异步任务？ [英] How to call an Async Task from the Contructor in a View Model?

问题描述

我正在尝试在加载我的应用程序时填充查找编辑列表，但我需要将其称为异步。

I am trying to populate a look up edit list on load of my application, but I need to call it async.

如何完成此操作？ 我在网上看到了一些答案，但没有一个有效。

How can this be completed?  I've seen some answers online, but none of them have worked.

谢谢。

推荐答案

你好ttaylor29，

Hi ttaylor29,

这是一个简单的样本供你参考。

Here is a simple sample for your reference.

#XAML

<Window x:Class="WpfApp1.AsyncLoadedDemo"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="AsyncLoadedDemo" Height="300" Width="300">
    <Grid>
        <ListBox HorizontalAlignment="Left" 
                 Height="240" Margin="10,10,10,10" 
                 VerticalAlignment="Top" Width="260"
                 x:Name="listBox1"
                 ItemsSource="{Binding Lists}"/>

    </Grid>
</Window>

#Code Behind

#Code Behind

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Threading.Tasks;
using System.Windows;

namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for AsyncLoadedDemo.xaml
    /// </summary>
    public partial class AsyncLoadedDemo : Window
    {
        public ObservableCollection<string> Payments { get; set; }
        public AsyncLoadedDemo()
        {
            InitializeComponent();
            this.DataContext = new AsyncLoadedDemoViewModel();
        }
    }

    public class AsyncLoadedDemoViewModel : DependencyObject
    {
        public List<string> Lists
        {
            get { return (List<string>)GetValue(ListsProperty); }
            set { SetValue(ListsProperty, value); }
        }

        // Using a DependencyProperty as the backing store for Lists.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty ListsProperty =
            DependencyProperty.Register("Lists", typeof(List<string>), typeof(AsyncLoadedDemoViewModel), new PropertyMetadata(null));

        public AsyncLoadedDemoViewModel()
        {
            TaskMethod();
        }

        public async void TaskMethod()
        {
            await Taskt();
        }

        public Task Taskt()
        {
            return Task.Run(() =>
            {
                List<string> l;
                using (var db = new EFDemoContext())
                {
                    l = db.payments.Select(t => t.PaymentMode).ToList();
                }

                this.Dispatcher.Invoke(
                    () =>
                    {
                        Lists = l;
                    }
                    );
            });
        }
    }

}

祝你好运，

张龙

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