c# - 任务、等待和 ManagementObjectCollection

Question

我试图使用 Lambda 表达式发现连接到系统的所有逻辑磁盘，并使用 wait 关键字异步执行该函数。除了返回语句之外，一切似乎都很好。

return(Search.Get()); 由于以下错误而无法编译:

"Cannot convert lambda expression to delegate type 'System.Func>' because some of the return types in the block are not implicitly convertible to the delegate return type (CS1662) - D:\PugApplications\Pug_AdvancedControls\Pug_AdvancedControls\Pug_FileSystemTree\Pug_FileSystemNode.cs:34,14

我该怎么做？我读到的所有内容都表明这应该有效。

Pug_DriveType 只是我为镜像 Win32 DriveType 枚举而编写的一个枚举。

//读取驱动器

Func<Pug_DriveType, Task<ManagementObjectCollection>> ReadTask = (Pug_DriveType DT) =>
{

    StringBuilder Query =
        new StringBuilder("SELECT * FROM Win32_LogicalDisk WHERE DriveType=\"")
        .Append((int)DT).Append("\"");

    ManagementObjectSearcher Search = new ManagementObjectSearcher(Query.ToString());

    return (Search.Get());
};

感谢您的帮助 丹尼

Answer 1

我认为你想要更多类似这样的东西:

Func<Pug_DriveType, Task<ManagementObjectCollection>> ReadTask = async (Pug_DriveType DT) =>
{

    StringBuilder Query =
        new StringBuilder("SELECT * FROM Win32_LogicalDisk WHERE DriveType=\"")
        .Append((int)DT).Append("\"");

    ManagementObjectSearcher Search = new ManagementObjectSearcher(Query.ToString());

    return await Task.Run(() => Search.Get());
};

或者可能:

Func<Pug_DriveType, Task<ManagementObjectCollection>> ReadTask = (Pug_DriveType DT) =>
{

    StringBuilder Query =
        new StringBuilder("SELECT * FROM Win32_LogicalDisk WHERE DriveType=\"")
        .Append((int)DT).Append("\"");

    ManagementObjectSearcher Search = new ManagementObjectSearcher(Query.ToString());

    return Task.Run(() => Search.Get());
};

(取决于您最终可能会在其中放入匿名方法的其他内容。)

以上任一情况都会导致您的匿名方法返回 Task<ManagementObjectCollection> ，已声明的委托(delegate)类型变量的返回类型，委托(delegate)实例被分配到该变量。您收到的错误告诉您 lambda 表达式返回的类型与为表达式推断的委托(delegate)类型(基于变量的类型)不同。