xaml页面，一个按钮，一个lable，lable用来更新等待的时间。点击按钮，每过1秒，label的数值+1,直到任务结束。

<Window x:Class="WpfApp2.MainWindow"
        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:WpfApp2"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Button Content="Button" HorizontalAlignment="Left" Margin="350,0,0,0" VerticalAlignment="Center" Height="72" Width="149" Click="Button_Click"/>
        <Label Content="0" HorizontalAlignment="Left" Margin="350,281,0,0" VerticalAlignment="Top"  x:Name="Lab"/>

    </Grid>
</Window>

.cs代码

 private async void Button_Click(object sender, RoutedEventArgs e)
 {
     bool isOk = false;
     Wait((result)=>isOk = result);
     while (!isOk)
     {
         //等待耗时任务结束，界面的Label加1
         await Task.Delay(1000);
         Lab.Content = Convert.ToInt32(Lab.Content) + 1;
     }
 }

 private async void Wait(Action<bool> callback)
 {
     bool isok = false;
     //耗时任务
     for (int i = 0; i < 10; i++)
     {
         await Task.Delay(1000);
     }
     isok = true;
     callback?.Invoke(isok);
 }