命名参数和可选参数在.NET中的使用

原文发布时间为：2011-04-25 —— 来源于本人的百度文章 [由搬家工具导入]

Named and Optional Arguments

class NamedExample
{
staticvoid Main(string[] args)
{
// The method can be called in the normal way, by using positional arguments.
Console.WriteLine(CalculateBMI(123, 64));

// Named arguments can be supplied for the parameters in either order.
Console.WriteLine(CalculateBMI(weight: 123, height: 64));
Console.WriteLine(CalculateBMI(height: 64, weight: 123));

// Positional arguments cannot follow named arguments.
// The following statement causes a compiler error.
//Console.WriteLine(CalculateBMI(weight: 123, 64));

// Named arguments can follow positional arguments.
Console.WriteLine(CalculateBMI(123, height: 64));
}

staticint CalculateBMI(int weight, int height)
{
return (weight * 703) / (height * height);
}

}

 

==================Optional Arguments

namespace OptionalNamespace
{
class OptionalExample
{
staticvoid Main(string[] args)
{
// Instance anExample does not send an argument for the constructor's
// optional parameter.
ExampleClass anExample = new ExampleClass();
anExample.ExampleMethod(1, "One", 1);
anExample.ExampleMethod(2, "Two");
anExample.ExampleMethod(3);

// Instance anotherExample sends an argument for the constructor's
// optional parameter.
ExampleClass anotherExample = new ExampleClass("Provided name");
anotherExample.ExampleMethod(1, "One", 1);
anotherExample.ExampleMethod(2, "Two");
anotherExample.ExampleMethod(3);

// The following statements produce compiler errors.

// An argument must be supplied for the first parameter, and it
// must be an integer.
//anExample.ExampleMethod("One", 1);
//anExample.ExampleMethod();

// You cannot leave a gap in the provided arguments.
//anExample.ExampleMethod(3, ,4);
//anExample.ExampleMethod(3, 4);

// You can use a named parameter to make the previous
// statement work.
anExample.ExampleMethod(3, optionalint: 4);
}
}

class ExampleClass
{
privatestring _name;

// Because the parameter for the constructor, name, has a default
// value assigned to it, it is optional.
public ExampleClass(string name = "Default name")
{
_name = name;
}

// The first parameter, required, has no default value assigned
// to it. Therefore, it is not optional. Both optionalstr and
// optionalint have default values assigned to them. They are optional.
publicvoid ExampleMethod(int required, string optionalstr = "default string",
int optionalint = 10)
{
Console.WriteLine("{0}: {1}, {2}, and {3}.", _name, required, optionalstr,
optionalint);
}
}

// The output from this example is the following:
// Default name: 1, One, and 1.
// Default name: 2, Two, and 10.
// Default name: 3, default string, and 10.
// Provided name: 1, One, and 1.
// Provided name: 2, Two, and 10.
// Provided name: 3, default string, and 10.
// Default name: 3, default string, and 4.

}