C#中如何基于Dictionary运行委托？解决CS0411编译错误

问题原因 #

你遇到的CS0411错误，核心原因是Dictionary的Select方法遍历的元素是KeyValuePair<SomeObject, SomeParams>类型，而你直接传递的GetMyObject2方法需要两个独立的参数SomeObject和SomeParams，编译器无法自动把KeyValuePair拆解成两个参数匹配你的方法签名，因此抛出类型不匹配的编译错误。

两种修复方案 #

方案1：用Lambda表达式显式拆解KeyValuePair #

在Select中通过lambda把KeyValuePair的Key和Value分别传给GetMyObject2，代码如下：

private readonly Dictionary<SomeObject, SomeParams> m_objectsList2 = 
                                                 new Dictionary<SomeObject, SomeParams>();

public Task<IList<Auto>> Todo2(SomeParams @params)
{
    IEnumerable<Auto> matches = m_objectsList2.Select(kvp => GetMyObject2(kvp.Key, kvp.Value));
    return Task.FromResult<IList<Auto>>(matches.ToArray());
}

private Auto GetMyObject2(SomeObject s, SomeParams p)
{
    Auto newAuto = new Auto();
    // ...你的业务逻辑代码
    return newAuto;
}

注意：params是C#关键字，建议改成@params避免语法冲突

方案2：修改GetMyObject2的参数为KeyValuePair #

直接把方法参数改为KeyValuePair<SomeObject, SomeParams>，在方法内部取出需要的Key和Value：

private readonly Dictionary<SomeObject, SomeParams> m_objectsList2 = 
                                                 new Dictionary<SomeObject, SomeParams>();

public Task<IList<Auto>> Todo2(SomeParams @params)
{
    IEnumerable<Auto> matches = m_objectsList2.Select(GetMyObject2);
    return Task.FromResult<IList<Auto>>(matches.ToArray());
}

private Auto GetMyObject2(KeyValuePair<SomeObject, SomeParams> kvp)
{
    SomeObject s = kvp.Key;
    SomeParams p = kvp.Value;
    Auto newAuto = new Auto();
    // ...你的业务逻辑代码
    return newAuto;
}

内容的提问来源于stack exchange，提问作者4est