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object reference not set to an instance of an object (file.move)

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Join Date: Feb 2009
Posts: 35
#1: Mar 11 '09
I'm getting the object reference error somewhere in my code. It didn't exactly tell me where, and I think I've narrowed it down to this line:

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  1. File.Move(tmpDlPath + fileName, dlPath + "\\" + set+ "\\_thumb.jpg");
When I comment out this line, my program runs just fine. Before this line I check to see if both directories exist and if the file exists, but that doesn't seem to help.

Any ideas?
tlhintoq's Avatar
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#2: Mar 11 '09

re: object reference not set to an instance of an object (file.move)

Its hard to say from just one line but...

When Visual Studio breaks it should be giving you a line where it breaks.
Possibility: tmpDlPath + Filename may need a break in between "\\".
Maybe tempDlPath isn't set?
Maybe dlPath isn't set?
Breakpoints along here should help
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#3: Mar 12 '09

re: object reference not set to an instance of an object (file.move)

Here's more of what I have:

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  1. if (Directory.Exists(tmpDlPath) && File.Exists(tmpDlPath + fileName) && Directory.Exists(dlPath + "\\" + set))
  2. {
  3.     try
  4.     {
  5.         File.Move(tmpDlPath + fileName, dlPath + "\\" + set+ "\\ThumbNail.jpg");
  6.     }
  7.     catch { }
  8. }
tmpDlPath already has a "\" at the end of it. Visual Studio doesn't give me a specific line where the error occurs.
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#4: Mar 12 '09

re: object reference not set to an instance of an object (file.move)

When the program breaks, what line does it break on? What line is highlighted and has the yellow arrow pointing at?
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#5: Mar 13 '09

re: object reference not set to an instance of an object (file.move)

I think it will help you to track problem

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  1. string filePath = dlPath + "\\" + set+ "\\ThumbNail.jpg"; 
  2. if (Directory.Exists(tmpDlPath) && File.Exists(tmpDlPath + fileName) && File.Exists(filePath)) 
  3. { 
  4.     try 
  5.     { 
  6.         File.Move(tmpDlPath + fileName, filePath); 
  7.     } 
  8.     catch (Exception ex)
  9.    { } 
  10. } 
  11. else
  12. {
  13.  MessageBox("Source or destination path is not valid");
  14. }
  15.  
tlhintoq's Avatar
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#6: Mar 13 '09

re: object reference not set to an instance of an object (file.move)

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  1. string filePath = dlPath.TrimEnd('\\') + "\\" + set + "\\Thumbnail.jpg";
  2. // This ensures there is only one "\\" whether or not dlPath already had it on the end or not.
  3.  
Quote:
if (Directory.Exists(tmpDlPath) && File.Exists(tmpDlPath + fileName) && File.Exists(filePath))

Quote:
File.Move(tmpDlPath + fileName, filePath);
If you have confirmed that filePath exists in your if statement then it is not reasonable to expect the move to be successful since their is already a file of that name at the target location.
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Posts: 35
#7: Mar 17 '09

re: object reference not set to an instance of an object (file.move)

Quote:

Originally Posted by tlhintoq View Post

When the program breaks, what line does it break on? What line is highlighted and has the yellow arrow pointing at?

Originally, it was breaking in my Program.cs file (the namespace is edited out):

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  1. namespace XXXXXXXXX
  2. {
  3.     static class Program
  4.     {
  5.         /// <summary>
  6.         /// The main entry point for the application.
  7.         /// </summary>
  8.         [STAThread]
  9.         static void Main()
  10.         {
  11.             Application.EnableVisualStyles();
  12.             Application.SetCompatibleTextRenderingDefault(false);
  13.             Application.Run(new XXXXXXXXX()); // Breaks at this line. 
  14.         }
  15.     }
  16. }
The error is:
TargetInvocationException was unhandled.
Exception has been thrown by the target of an invocation.

I then added in a try-catch:
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  1. static void Main()
  2. {
  3.     Application.EnableVisualStyles();
  4.     Application.SetCompatibleTextRenderingDefault(false);
  5.     try
  6.     {
  7.         Application.Run(new XXXXXXXXX());
  8.     }
  9.     catch (Exception ex)
  10.     {
  11.         MessageBox.Show(ex.InnerException.Message);
  12.     }
  13. }
And now I just get a MessageBox with "Object Reference Not set to an instance of an object" with no line indication. I guessed at where the error was occurring (in one of my background workers) and narrowed it down to that one File.Move line.
tlhintoq's Avatar
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#8: Mar 17 '09

re: object reference not set to an instance of an object (file.move)

Let's start by changing that behavior so you can see where the actual exception is taking place.



Quote:
And now I just get a MessageBox with "Object Reference Not set to an instance of an object"
Just have to set breakpoints in the area of the failure and look at the variables and see which ones are null.



Set a breakpoint and walk it through one command at a time with the F-10 key.
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Posts: 35
#9: Mar 17 '09

re: object reference not set to an instance of an object (file.move)

Thank You tlhintoq for showing me that method! I was able to track down the null reference! That is a really handy tool! I appreciate your help very much!
tlhintoq's Avatar
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#10: Mar 17 '09

re: object reference not set to an instance of an object (file.move)

My pleasure... So what was it anyway?
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#11: Mar 17 '09

re: object reference not set to an instance of an object (file.move)

When the file is moved over to that directory, a listview control is updated. I check the listview to see if it's already there.

Here is my fixed code:

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  1. ListViewItem toRemove = new ListViewItem();
  2. toRemove = lv_sets.FindItemWithText(sName);
  3. if (toRemove != null)
  4. {
  5.     toRemove.Remove();
  6. }
toRemove was sometimes empty and then calling toRemove.Remove() would produce the error.
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