异步等待停止... C# WPF

Question

我有一个函数，它获取一个 Func 作为参数，并以异步方法在任务内部执行它，以便在函数运行时显示不确定的进度条....

private async void Invoke(Func<string> function)
{
       if(calculation?.Status == TaskStatus.Running) await calculation;
       calculation = Task.Run(function);
       InvokeA(() => prg.Height = double.NaN);
       InvokeA(() => prg.Visibility = Visibility.Visible);
       Result = await calculation;
       InvokeA(() => prg.Visibility = Visibility.Hidden);
       InvokeA(() => prg.Height = 0);
}

问题是函数何时达到：

Result = await Calculation;

它有点停止...它永远不会真正设置值或关闭进度条。

如果键为 Enter，则从 Textbox.KeyDown 方法调用调用：

if (SpecialCommands.DoesExist(Text))
    {
          Invoke(() => SpecialCommands.Invoke(Parameter));
          if (!string.IsNullOrEmpty(Result)) Text += $"   --->   {Result}";
     }

变量定义：

calculation = Task<string>
Result = string
prg = ProgressBar
Parameter = string that isn't connected to the UI

Answer 1

我使用以下内容创建了一个标准的新 WPF 应用程序项目XAML

<Window x:Class="WpfApplication1.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:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Canvas>
        <Button x:Name="button" Content="Button" Canvas.Left="62" Canvas.Top="40" Width="75" Click="button_Click"/>
        <ProgressBar x:Name="prg" Height="23" Canvas.Left="62" Canvas.Top="265" Width="347" IsIndeterminate="True"/>
    </Canvas>
</Window>

和代码隐藏

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    Task<string> calculation;
    string Result;
    string Text;

    private async void button_Click(object sender, RoutedEventArgs e)
    {
        await Invoke(() => Foo());
        if (!string.IsNullOrEmpty(Result)) Text += $"   --->   {Result}";
    }

    private async Task Invoke(Func<string> function)
    {
        if (calculation?.Status == TaskStatus.Running) await calculation;
        calculation = Task.Run(function);
        InvokeA(() => prg.Height = double.NaN);
        InvokeA(() => prg.Visibility = Visibility.Visible);
        Result = await calculation;
        InvokeA(() => prg.Visibility = Visibility.Hidden);
        InvokeA(() => prg.Height = 0);
    }

    private void InvokeA(Action a) { a(); }

    static string Foo()
    {
        Thread.Sleep(5000);
        return "Bar";
    }
}

它按预期工作。所以问题出在您提供的其他地方。

EDIT 根据您的评论，值得尝试以下操作，因为那是您代码的错误部分：

首先，将Invoke方法的签名改为

private async Task Invoke(Func<string> function)

然后使用

await Invoke(() => Foo());
if (!string.IsNullOrEmpty(Result)) Text += $"   --->   {Result}";

希望对您有所帮助。

异步等待停止... C# WPF

Async Await Stops... C# WPF

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