为什么不能点,矩形作为可选参数? [英] Why can't Point and Rectangle be used as optional parameters?
问题描述
我想要一个可选的参数传递给一个几何函数,名为偏移
,这可能会或可能不会进行规定,但是C#不允许我这样做以下任一。有没有办法做到这一点?
I'm trying to pass an optional argument to a geometry function, called offset
, which may or may not be specified, but C# doesn't allow me to do any of the following. Is there a way to accomplish this?
-
Null作为默认
错误:类型'值'不能用作默认参数,因为没有标准转换到类型System.Drawing.Point
Error: A value of type '' cannot be used as a default parameter because there are no standard conversions to type 'System.Drawing.Point'
public void LayoutRelative(.... Point offset = null) {}
空默认
错误:偏移必须是一个编译时间常数默认参数值
Error: Default parameter value for 'offset' must be a compile-time constant
public void LayoutRelative(.... Point offset = Point.Empty) {}
推荐答案
如果您的默认值,不需要任何特殊的初始化,你并不需要使用可空类型,或者创建不同的重载。
您可以使用默认
关键字:
If your default value doesn't require any special initialization, you don't need to use a nullable type or create different overloads.
You can use the default
keyword:
public void LayoutRelative(.... Point offset = default(Point)) {}
如果你想使用可空类型,而不是:
If you want to use a nullable type instead:
public void LayoutRelative(.... Point? offset = null)
{
if (offset.HasValue)
{
DoSomethingWith(offset.Value);
}
}
这篇关于为什么不能点,矩形作为可选参数?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!