Take information from another window

Question

1.00/5 (1 vote)

See more:

Hi,
I have a ListView within a Windows 1 and a listbox in Window2. I need to take the data of the first column in ListView (window1) and put this data in the ListBox (window2).
This is the code:

In Window1:

VB

Private Sub Window1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles Acqui.Closing
   
        Dim firstColunm As New List(Of String)()
        For Each item As ListViewData In Lista.listView1.Items
            firstColunm.Add(item.Identifiant)
        Next

    End Sub

Identifiant is the first column of my listview.
ListViewData is a class who has the property of ListView.

In Window2:

VB

Public Class Window2

    Public Sub New()
        InitializeComponent()
    End Sub

    Public Sub New(ByVal source As List(Of String))
        Me.DataContext = source
        InitializeComponent()
    End Sub
End Class

When i close the window1 i have the next error:
An unhandled exception of type 'System.NullReferenceException' occurred in PresentationFramework.dll
Additional information: Object reference not set to an instance of an object.

What is the problem?
Thanks

Posted 18-Aug-13 6:41am

alonetmr

Add a Solution

Comments

Sergey Alexandrovich Kryukov 18-Aug-13 12:56pm

You need to use the debugger, to start with.
—SA

alonetmr 18-Aug-13 13:13pm

I forgot:
The exception is here:
For Each item As ListViewData In Lista.listView1.Items
firstColunm.Add(item.Identifiant)
Next

Maciej Los 18-Aug-13 17:10pm

Does Window1 is your main window?

alonetmr 19-Aug-13 2:25am

Hi, not. In fact,
The windows1 is within an ViewBox which is call clicking a button in the window1. My mainWindow is other thing.

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Answer 1 · 2013-08-18T06:57:00

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA

Maciej Los · Answer 2 · 2013-08-18T11:18:00

Solution 2

Please, read my comment to the question.
In my opinion you need to read this: WPF Windows Overview[^] and understand Window Lifetime Events.

Posted 18-Aug-13 11:18am

Maciej Los

Comments

Sergey Alexandrovich Kryukov 18-Aug-13 18:23pm

Hm. At first glance, this information is not related to the problem. But indirectly, the root cause of the problem might be there, and more thorough understanding of lifetime may help to write correct code of closing the application. 5ed.
—SA

Maciej Los 19-Aug-13 3:16am

Thank you, Sergey ;)