Why else not working with MVVM?

Question

Hi,

I have the lines

  homeworkJ = new HomeworkJViewModel();
  homeworkJ = homeworkJ.GetHomeworkJID(System.Convert.ToInt32(ywdwStartJ1S);

 if (homeworkJ._id > 0) // != null)
    {
        System.Diagnostics.Debug.WriteLine("homeworkJ != null ");
        // Works perfect
    }
 else //if (homeworkJ == null)
     {
         System.Diagnostics.Debug.WriteLine("homeworkJ == null ");
          //Error
         //A first chance exception of type 'System.NullReferenceException' occurred in Class Time.exe
}

else statment not working.
What am I missing?

Thanks

---

ADRIAN DIBU

Answer 1

homeworkJ must be null, that's why you are getting the null reference exception. Make your if like - if (homeworkJ != null && homeworkJ._id > 0) to fix the exception.

---

Thanks,

Sachin

My Samples

Answer 2

Hi,

Thanks for the prompt answer.

I tried same: if working else not.

My problem is:

I want if the result of
 homeworkJ = homeworkJ.GetHomeworkJID(System.Convert.ToInt32(ywdwStartJ1S);

is null to do some action.

 Maybe the fact

 homeworkJ = new HomeworkJViewModel();

gives homework is not null no mater if GetHomeworkJID is null

Thanks

---

ADRIAN DIBU

Answer 3

Try this

if (homeworkJ == null)
            {
                // Do something here on null
            }
            else if (homeworkJ._id > 0)
            {
                // Do something here if id is > 0
            }
            else 
            {
                // Do something here if id is not > 0 and also not null
            }

Also, homeworkJ value will overwritten after call to GetHomeworkJID, so it can be null or not null depending what function returns. 

---

Thanks,

Sachin

My Samples

Answer 4

Hi,

Not working

 homeworkJ = homeworkJ.GetHomeworkJID(System.Convert.ToInt32(ywdwStartJ1S);

If data exist all is OK.

If no data null error.

if (homeworkJ == null) or if (homeworkJ != null)
 Gives error because it checks if is null and it is so the error come.

How can I pass the line when no data exist.

---

ADRIAN DIBU

Answer 5

Hi,

I tried

  homeworkJ = new HomeworkJViewModel();

  if (homeworkJ != null)
                {
                    System.Diagnostics.Debug.WriteLine("");
                }
                else
                {
                    System.Diagnostics.Debug.WriteLine("homeworkJ == null");
               

I got

homeworkJ != null

means even no data homeworkJ is not null.

 So why the lack of data in

homeworkJ = homeworkJ.GetHomeworkJID(System.Convert.ToInt32(ywdwStartJ1S);

gives null error and impossibility to do something if no data.

Thanks

---

ADRIAN DIBU

Answer 6

Sorry, I am not able to understand it. If possible, upload a small project where you are facing the issue and what should be expected results.

---

Thanks,

Sachin

My Samples