错误返回时无法将类型'string'隐式转换为'System.DateTime'

Question

I trying to add a propriety into a class but I'm getting the error: Error Cannot implicitly convert type 'string' to 'System.DateTime' on the else return.

public DateTime BookDate
        {
            get
            {
                if (this.PXP.BookDate.HasValue)
                {
                    return this.PXP.BookDate.Value;
                }
                else return "";
            }
        }

I am not sure what to return here. I have to return something or else I get the error: not all code paths return a value. BookDate is being called from another class:

 public JobPXP PXP { get; set; }

I know this question is very simple.. and the answer is I was just missing the ? after DataTime. Thank you everyone for their answers

Answer 1

public DateTime BookDate
    {
        get
        {
            if (this.PXP.BookDate.HasValue)
            {
                return this.PXP.BookDate.Value;
            }
            else return "";
        }
    }

From your code it looks like you want to pass empty date when this.PXP.BookDate.HasValue is false.

The error is for - else return ""; statement. You are trying to pass string in return statement. Here is my suggestion (I am assuming this.PXP.BookDate is nullable DateTime as it looks from your code.)

public DateTime? BookDate
    {
        get
        {                
            return this.PXP.BookDate;                
        }
    }

Answer 2

I am not sure what to return here

If you are not sure what to return, probably you want to return null . However, the problem is that BookDate property is DateTime , which does not allow null s. However, Nullable<DateTime> , or simply DateTime? does allow null s. Since this.PXP.BookDate is nullable, you can return it directly, like this:

public DateTime? BookDate {
    get {
        return this.PXP.BookDate;
    }
}

Another solution is to make a method that would get an optional BookDate if it exists, similar to TryGetValue method of IDictionary<K,V> :

public bool TryGetBookDate(out DateTime res) {
    res = this.PXP.BookDate ?? default(DateTime);
    return this.PXP.BookDate.HasValue;
}

Answer 3

DateTime can not be null, so you can't return null . A string is also an invalid option. You've basically got two options here:

Either return a specific value of DateTime , such as DateTime.MinValue (which is 01.01.0001 ), or use a Nullable<DateTime> instead (equivalent to DateTime? ).

This last approach will let you return a Null values instead of an actual date, but will change the signature of the method, which in turn, will require handling when calling the method.

You'll still have to handle special cases outside the method if you use DateTime.MinValue instead though, so I'd say it's up to you to choose what suits your situation best.

Answer 4

Another Way:

public DateTime BookDate
        {
            get
            {
               DateTime dt = DateTime.MinValue;//you default datetime here
               DateTime.TryParse(Convert.ToString(this.PXP.BookDate.Value),out dt)
               return dt;  

            }
    }