How To pass Optional Arguments

问题

I have one function having two fixed arguments. But next arguments are not fixed, there can be two or three or four of them.

It's a runtime arguments so how can I define that function?

My code looks like:

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, dynamic arguments comming it should be 2 or 3)
        {

        return null;
    }

回答1:

1) params (C# Reference)

public ObservableCollection<ERCErrors>ErrorCollectionWithValue
                (string ErrorDode, int MulCopyNo, params object[] args)
{
    //...
}

2) Named and Optional Arguments (C# Programming Guide)

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, object arg1 = null, int arg2 = int.MinValue)
{
    //...
}

3) And maybe simple method overloading would still suit better, separating method logic to different methods? Under this link you can also find another description of named and optional parameters

回答2:

One approach is to have overloaded methods

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, int param1)
{
   //do some thing with param1
}

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, int param1,int param2)
{
   //do some thing with param1 and param3
}

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, int param1, int param2, int param3)
    {
       //do some thing with param1, param2 and param3
    }

then all these would be valid

var err = ErrorCollectionWithValue("text", 10, 1);
var err = ErrorCollectionWithValue("text", 10, 1,2);
var err = ErrorCollectionWithValue("text", 10, 1,2,3);

Another approach is to use optional parameters. With this you need only one method as opposed to the 3 in the first approach.

public ObservableCollection<ERCErrors> ErrorCollectionWithValue
    (string ErrorDode, int MulCopyNo, int param1 = 0, int param2 = 0, optional int param3 = 0)
{

}

these are still valid

var err = ErrorCollectionWithValue("text", 10, 1); //defaults param2 and param3 to 0
var err = ErrorCollectionWithValue("text", 10, 1,2); //defaults param3 to 0
var err = ErrorCollectionWithValue("text", 10, 1,2,3);

To skip any of the optional parameters, you need to use named parameters and this which is only supported in C# 4.0 and above

var err = ErrorCollectionWithValue("text", param3: 5); //skipping param1 and param2

In the other two approaches, you can't skip the order of the parameters.

回答3:

You could go with params, if the number of argument may vary:

public ObservableCollection<ERCErrors> ErrorCollectionWithValue(string errorCode, int num, params object[] args) 
{ 
  foreach(object obj in args)
{
  //process args.
}
}

来源：https://stackoverflow.com/questions/12577730/how-to-pass-optional-arguments

标签

optional-parameters