C# 返回一个列表或一个 int

Question

Is it possible to return a List OR an int in a method?

Something like:

• if it succeeded: return List
• if it failed: return int (that gives an error number) or string with error message.

(failed as in no exceptions but the values are incorrect, like PointF.X = below 0 or Lowest value is over 10).

Now I'm doing it like this:

public List<PointF> GetContourInfoFromFile(string a_file)
{
    ListContourPoints.Clear();
    List<string> textLines = new List<string>();

    bool inEntitiesPart = false;
    bool inContourPart = false;

    try
    {
        foreach (string str in File.ReadAllLines(a_file))
        {
            textLines.Add(str);//Set complete file in array
        }

        for (int i = 0; i < textLines.Count; i++)
        {
            //read complete file and get information and set them in ListContourPoints
        }

        //Check Coordinate values
        for (int i = 0; i < ListContourPoints.Count; i++)
        {
            //Coordinates are below -1!
            if (ListContourPoints[i].X < -1 || ListContourPoints[i].Y < -1)
            {
                ListContourPoints.Clear();
                break;
            }
            //Lowest X coordinate is not below 10!
            if (mostLowestXContour(ListContourPoints) > 10)
            {
                ListContourPoints.Clear();
                break;
            }
            //Lowest Y coordinate is not below 10!
            if (mostLowestYContour(ListContourPoints) > 10)
            {
                ListContourPoints.Clear();
                break;
            }
        }
    }
    catch (Exception E)
    {
        string Error = E.Message;
        ListContourPoints.Clear();
    }
    return ListContourPoints;
}

When I do it like this, I know there is something wrong with te values.. but not specifically what.

So how can I solve this? If it's not possible with returning a list OR string/int, what's the best solution?

Answer 1

You can

Solution 1:

throw exception if error, and in your code above do a try catch

Delete the part catch in your function, and when you call you function do it in try catch like this:

try
{
    List<PointF> result = GetContourInfoFromFile(youfile);
}
catch (Exception E)
{
    string Error = E.Message;
}

Solution 2:

return an object with Listresult and error as property

Answer 2

Instead of returning a number, you can throw an exception from the catch block so that it can be caught by the outer exception handler.

Here's a sample:

public void MainMethod()
{
    try
    {
        var myList = SomeMethod();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message); // prints out "SomeMethod failed."
    }
}

public List<object> SomeMethod()
{
    try
    {
        int i = 1 + 1;

        // Some process that may throw an exception

        List<object> list = new List<object>();
        list.Add(1);
        list.Add(i);

        return list;
    }
    catch (Exception ex)
    {
        Exception newEx = new Exception("SomeMethod failed.");
        throw newEx;
    }
}

Answer 3

you could create a wrapper class which holds either the value or the errorcode. Example:

public class Holder<T>
{
    private Holder(T value)
    {
        WasSuccessful = true;
        Value = value;
    }

    private Holder(int errorCode)
    {
        WasSuccessful = false;
        ErrorCode = errorCode;
    }

    public bool WasSuccessful { get; }
    public T Value { get; }
    public int ErrorCode { get; }

    public static Holder<T> Success(T value)
    {
        return new Holder<T>(value);
    }

    public static Holder<T> Fail(int errorCode)
    {
        return new Holder<T>(errorCode);
    }
}

Usage:

public Holder<PointF> MyFunc()
{
    try
    {
        //
        return Holder<PointF>.Success(new PointF());
    }
    catch
    {
        return Holder<PointF>.Fail(101);
    }
}

Answer 4

one solution would be to return object

public object GetContourInfoFromFile(string a_file)
{

}

and in the method where you call this try to cast to both int and list and see which one succeeds.

a more elaborate solution would be to have a class

public class YourClassName{
   public List<PointF> YourList {get; set;} //for success
   public int YourVariable {get; set} // for failure
   public string YourMEssage {get; set} // for failure
}

and return that one

public YourClassName GetContourInfoFromFile(string a_file)
{

}