C# API Call: Null Exception at foreach loop

Question

I'm trying to map API JSON data into some properties of a class, and I'm getting the error below. I was able to narrow down the data entry causing this issue. [The value for PositionDateStart]

The script successfully creates an object off the properties, but once I call the object to test it using a foreach loop, it crashes and gives me this error.

My question is what could I write to tell the script to replace null with today's date if this comes up.

Thanks in advance!

Error Message:

NullReferenceException: Object reference not set to an instance of an object.

JSON Results @Console.WriteLine(json)

[
    {
        "EntryID": 41992,
        "Position": "Associate",
        "PositionDateEnd": "2020-05-15T00:00:00",
        "PositionDateStart": null
    }
]

Script

var json = await response.Content.ReadAsStringAsync();
Console.WriteLine(json); //JSON results above
var result = JsonConvert.DeserializeObject<List<Properties>>(json);

//Point at which code errors outs 
foreach (var item in result)
{
    Console.WriteLine(item.PositionDateStart);
    Console.WriteLine(item.PositionDateStart.GetType());
}

Class Properties

public class Properties
{
    public int EntryID { get; set; }

    public string Position { get; set; }

    public DateTime? PositionDateEnd { get; set; }

    public DateTime? PositionDateStart { get; set; }
}

TaiT's · Accepted Answer · 2019-08-07T17:27:28.740

1

You can simply assign current date if PositionDateStart is null then output to console anyway without errors since it will never be empty:

//Point at which code errors outs 
foreach (var item in result)
{
   if (item.PositionDateStart == null)
       item.PositionDateStart = DateTime.Now;
   Console.WriteLine(item.PositionDateStart);
   Console.WriteLine(item.PositionDateStart.GetType());
}

EDIT

As asked in comment, if you prefere to modify the class itself here is a variant through the get accessor so your foreach remains the same:

public class Properties
{
    public int EntryID { get; set; }

    public string Position { get; set; }

    public DateTime? PositionDateEnd { get; set; }

    private DateTime? _positionDateStart;
    public DateTime? PositionDateStart
    {
       get { return _positionDateStart == null ? DateTime.Now : _positionDateStart; }
       set { _positionDateStart = value; }
    }
}

edited Aug 07 '19 at 17:27

answered Aug 07 '19 at 15:49

TaiT's

2,532
2
13
25

Thank you. This worked. Do you know if it'd be possible to set this condition to the property in the Class Properties? – ChunkyFresh Aug 07 '19 at 17:08
1

@ChunkyFresh You should be able to do that. See my edits. And also pls approve the answer, that's already two ;). Happy coding! – TaiT's Aug 07 '19 at 17:28
You got it. I tried this at the class level,and it worked perfectly. One last thing thoug. I'm fairly new to C# sharp so I was wondering if you could point me to what I could read to understand the syntax you provided? Having a tough time deciphering what's going on inside the get/set part of it. – ChunkyFresh Aug 07 '19 at 18:49
The `?:` syntax is called the [conditional operator](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/conditional-operator). You can see it as an if/else in one single line. – TaiT's Aug 07 '19 at 22:05
Thank you. Appreciate all the help! – ChunkyFresh Aug 08 '19 at 14:54

score 0 · Answer 2 · answered Aug 07 '19 at 15:47

0

Try (not tested):

Console.WriteLine(item?.PositionDateStart ?? DateTime.Now);

The null condional and null coalese operators are explained here

answered Aug 07 '19 at 15:47

Peter Smith

5,321
8
46
72

score 0 · Answer 3 · answered Aug 07 '19 at 15:48

0

try the following code:

foreach (var item in result)
{
    if(item.PositionStartDate == null)
    {
        item.PositionDateStart = DateTime.Now;
    }
    Console.WriteLine(item.PositionDateStart.GetType());
}

answered Aug 07 '19 at 15:48

Örvar

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C# API Call: Null Exception at foreach loop

3 Answers3