首页> C#> ASP.NET Core如何能够将任何类型转换为ActionResult返回类型的控制器操作？

[HttpGet("test123")]
public ActionResult<string> Test123()
{
    return new OkResult();
}

这样编译可以,但是我想知道OkResult对象怎么可能转换为ActionResult< string&gt ;？ 这些类具有不同的继承链：
OkResult-> StatusCodeResult->动作结果
而ActionResult< TValue>仅实现IConvertToActionResult
换句话说,ActionResult< string>不是OkResult类的基本类型.

如果我手动执行此操作并将代码更改为：

[HttpGet("test123")]
public ActionResult<string> Test123()
{
    var a = new OkResult();
    var b = a as ActionResult<string>;  // Error CS0039

    return b;
}

该代码将不会编译并显示转换错误：

Error CS0039: Cannot convert type ‘Microsoft.AspNetCore.Mvc.OkResult’ to ‘Microsoft.AspNetCore.Mvc.ActionResult’ via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion

第一个代码如何工作而第二个代码却不工作呢？如何从没有通用基本类型的对象转换返回类型？

/// <summary>
/// Implictly converts the specified <paramref name="value"/> to an <see cref="ActionResult{TValue}"/>.
/// </summary>
/// <param name="value">The value to convert.</param>
public static implicit operator ActionResult<TValue>(TValue value)
{
    return new ActionResult<TValue>(value);
}

/// <summary>
/// Implictly converts the specified <paramref name="result"/> to an <see cref="ActionResult{TValue}"/>.
/// </summary>
/// <param name="result">The <see cref="ActionResult"/>.</param>
public static implicit operator ActionResult<TValue>(ActionResult result)
{
    return new ActionResult<TValue>(result);
}

Source

是什么允许在操作中使用多种返回类型.

[HttpGet("test123")]
public ActionResult<string> Test123() {
    if(someCondition) return "String value"; //<--String
    return Ok(); //<-- OkResult
}

当返回字符串时,调用ActionResult< TValue>(TValue值)运算符,并返回有效的ActionResult< TValue>.反之亦然.