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c# - 如何将此 C# lambda 转换为 VB.net？

问题描述

我很难将 C# 语句翻译成 VB。我不知道这是否是我使用的 lambda，但我不是那个专家，或者是分隔符，我对它的了解更少。根据 Microsoft 的说法，C# '=>' 符号可以以这两种不同的方式使用。

我遇到问题的 C# 代码行是：

RecurringJob.AddOrUpdate(() => TextBuffer.WriteLine("text"), Cron.Minutely);

它来自示例 hangfire.mvcApplication 项目中的 Startup.cs 文件。这是完整的课程：

public void Configuration(IAppBuilder app)
{
    GlobalConfiguration.Configuration.UseSqlServerStorage("DefaultConnection");
    app.UseHangfireDashboard();
    app.UseHangfireServer();
    RecurringJob.AddOrUpdate(
        () => TextBuffer.WriteLine("Recurring Job completed successfully!"), 
        Cron.Minutely);
}

the TextBuffer.WriteLine reference is:

public static void WriteLine(string value)
{
    lock (Buffer)
    {
        Buffer.AppendLine(String.Format("{0} {1}", DateTime.Now, value));
    }
}

这是我尝试过的，但并不准确；我尝试了很多变化：

RecurringJob.AddOrUpdate(Function() TextBuffer.WriteLine("text"), Cron.Minutely)

我在 Visual Studio 中得到的语法错误是：

Expression does not produce a value

我查看了 AddOrUpdate 的定义并看到了以下重载，但我不确定哪个是正确的选择，也不确定一旦我选择了正确的重载，语法会如何。

Public Shared Sub AddOrUpdate(methodCall As Expression(Of Action), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(methodCall As Expression(Of Action), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(methodCall As Expression(Of Func(Of Task)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(methodCall As Expression(Of Func(Of Task)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(recurringJobId As String, methodCall As Expression(Of Action), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(recurringJobId As String, methodCall As Expression(Of Action), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(recurringJobId As String, methodCall As Expression(Of Func(Of Task)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(recurringJobId As String, methodCall As Expression(Of Func(Of Task)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(methodCall As Expression(Of Action(Of T)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(methodCall As Expression(Of Action(Of T)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(methodCall As Expression(Of Func(Of T, Task)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(methodCall As Expression(Of Func(Of T, Task)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(recurringJobId As String, methodCall As Expression(Of Action(Of T)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(recurringJobId As String, methodCall As Expression(Of Action(Of T)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(recurringJobId As String, methodCall As Expression(Of Func(Of T, Task)), cronExpression As Func(Of String), Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")
Public Shared Sub AddOrUpdate(Of T)(recurringJobId As String, methodCall As Expression(Of Func(Of T, Task)), cronExpression As String, Optional timeZone As TimeZoneInfo = Nothing, Optional queue As String = "default")

我只是不明白该方法正在寻找什么或如何正确编写它。

标签： c#vb.netlambdahangfire

解决方案

VB.NET 有两个不同的 lambda 表达式：Function，它返回一个值，而Sub，它不。

在这种情况下，您要使用Sub，因为您的表达式不返回值。

RecurringJob.AddOrUpdate(Sub() TextBuffer.WriteLine("text"), Cron.Minutely)

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