如何在例程中使用MVVM更新UI中的属性

Question

我想建立一些倒数计数器。 问题是我的解决方案在10秒后仅显示起始值10和最后一个值1。 当然，我已经实现了INotifyPropertyChanged接口。 对该解决方案的任何建议？

<Button Content="Generuj"  Command="{Binding ButtonStart}"></Button>
<TextBox  Text="{Binding Counter, Mode=OneWay}"></TextBox>

private void ButtonStartClick(object obj)
{
    for (int i = 10; i > 0; i--)
    {
         System.Threading.Thread.Sleep(1000);
         Counter = i;
    }
}

Answer 1

使用Thread.Sleep，您将冻结GUI。 尝试使用计时器。 计时器将同时运行到您的GUI线程，因此不会冻结它。 此外，您还需要为计数器实现PropertyChanged事件。还要确保设置DataContext

    //create a dependency property you can bind to (put into class)
    public int Counter
    {
        get { return (int)this.GetValue(CounterProperty); }
        set { this.SetValue(CounterProperty, value); }
    }

    public static readonly DependencyProperty CounterProperty =
        DependencyProperty.Register(nameof(Counter), typeof(int), typeof(MainWindow), new PropertyMetadata(default(int)));


    //Create a timer that runs one second and decreases CountDown when elapsed (Put into click event)
    Timer t = new Timer();
    t.Interval = 1000;
    t.Elapsed += CountDown;
    t.Start();

    //restart countdown when value greater one (put into class)
    private void CountDown(object sender, ElapsedEventArgs e)
    {
        if (counter > 1)
        {
            (sender as Timer).Start();
        }
        Counter--;
    }

Answer 2

您可以使用async await来引入轻量级延迟。

与计时器相比，它的主要优点是没有让代表挂钩和运行的风险。

在这个视图模型中我使用mvvmlight，但ICommand的任何实现都可以。

 …..
using System.Threading.Tasks;
using GalaSoft.MvvmLight.CommandWpf;
namespace wpf_99
{
public class MainWindowViewModel : BaseViewModel
{
    private int counter =10;

    public int Counter
    {
        get { return counter; }
        set { counter = value; RaisePropertyChanged(); }
    }

    private RelayCommand countDownCommand;
    public RelayCommand CountDownCommand
    {
        get
        {
            return countDownCommand
            ?? (countDownCommand = new RelayCommand(
             async () =>
             {
                 for (int i = 10; i > 0; i--)
                 {
                     await Task.Delay(1000);
                     Counter = i;
                 }
             }
             ));
        }
    }

当然不是很多，它与Counter结合在一起：

<Grid>
    <StackPanel>
    <TextBlock Text="{Binding Counter}"/>
        <Button Content="Count" Command="{Binding CountDownCommand}"/>
    </StackPanel>
</Grid>

Answer 3

您还可以在单​​独的线程中运行Counter

Task.Run(() =>
             {
                 for (int i = 10; i > 0; i--)
                 {
                     Counter = i;
                     Thread.Sleep(1000);
                 }
             });