Answered by:
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
Sunday, August 4, 2013 3:27 PM
Answers
-
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
- Edited by Sachin S Sunday, August 4, 2013 4:48 PM Oops, missed the object is used for func call
- Marked as answer by Matt SmallMicrosoft employee, Moderator Friday, August 9, 2013 3:12 PM
Sunday, August 4, 2013 4:44 PM
All replies
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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,SachinMy SamplesSunday, August 4, 2013 3:37 PM
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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
Sunday, August 4, 2013 4:06 PM -
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
- Edited by Sachin S Sunday, August 4, 2013 4:48 PM Oops, missed the object is used for func call
- Marked as answer by Matt SmallMicrosoft employee, Moderator Friday, August 9, 2013 3:12 PM
Sunday, August 4, 2013 4:44 PM -
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
Monday, August 5, 2013 12:17 AM -
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
Monday, August 5, 2013 12:40 AM -
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,SachinMy SamplesMonday, August 5, 2013 2:21 AM