C#:有一个"可选"参数,默认情况下使用所需参数的值

Question

如何为函数实现"可选"参数,以便在endMarker未给出时,我将使用所需参数中的值startMarker？我目前使用可空类型并检查是否endMarker为null我将其设置为startMarker

protected void wrapText(string startMarker, string? endMarker = null) { 
    if (endMarker == null)
        endMarker = startMarker; 
}

但现在的问题是我得到一个错误,说它无法string?投入string

(string)endMarker

我怎么可以投endMarker给string这样我就可以使用它？还是有更好的方法来实现这个？

Answer 1

This will work:

protected void wrapText(string startMarker, string endMarker = null) { 
    if (endMarker == null)
        endMarker = startMarker; 
}

In other words: remove the question mark from the string?. System.String is a reference type and can already be null. The Nullable<T> structure can only be used on value types.