grabarz121 grabarz121 - 3 months ago 19
ASP.NET (C#) Question

NullReferenceException using two constructor class

I'm new here. I can't find solution to my problem anywhere. I'm writing a project to school. I have two forms. In first form, I have a DataGridView object, when I'm storing data in a SQL Server database. I'm passing usernames from DataGridView to second form using code:

List<string> usersList = new List<string>();

for (int i = 0; i < dataGridViewUsers.RowCount; i++)
{
usersList.Add(dataGridViewUsers.Rows[i].Cells[1].Value.ToString());
}

AddFileForm addFile = new AddFileForm(usersList);
addFile.Show();


In second form in have following code:

private List<string> userNames;
private Files file;

public AddFileForm()
{
file = new Files();
userNames = new List<string>();
InitializeComponent();
}

public AddFileForm(List<string> _userNames)
{
this.userNames = _userNames;
InitializeComponent();
listBoxUserList.DataSource = _userNames;
}

private AddFileForm(Files _file)
{
this.file = _file;
InitializeComponent();
listBoxUserList.SelectedValue = _file.userName;
listBoxItems.SelectedValue = _file.directory;
}


Passing data from first form works fine, but the problem starts when I try to pass data from listBoxUserList and listBoxItems to database using stored-procedures. I'm adding data to listBoxItems manually. NullReferenceException occur on a button click, here:

private void buttonAdd_Click(object sender, EventArgs e)
{
if (listBoxUserList.SelectedItems.Count != 0 && listBoxItems.SelectedItems.Count != 0)
{
file.userName = listBoxUserList.SelectedValue.ToString();
file.directory = listBoxItems.SelectedValue.ToString();
try
{
DBConnection connection = new DBConnection();
connection.AddFile(file);

MessageBox.Show("File added to database.");
}
catch (Exception)
{
MessageBox.Show("Failed database connection!");
}
}
else
{
MessageBox.Show("First, select items to add to database");
}
}


Value from both listBoxes is not null, I have checked this. The main problem probably is in class constructor. My stored procedure works fine, when I was comment constructor who passing data from first form, it perfectly passing data to database. So, what's wrong? What i should do with constructors of class, it will work property in both cases?

I'm pasting error details

System.NullReferenceException was unhandled
HResult=-2147467261
Message=Odwołanie do obiektu nie zostało ustawione na wystąpienie obiektu.
Source=FilesEncoding
StackTrace:
w FilesEncoding.AddFileForm.buttonAdd_Click(Object sender, EventArgs e) w C:\Users\Grabarz\Documents\Visual Studio 2010\Projects\FilesEncoding\FilesEncoding\AddFileForm.cs:wiersz 110
w System.Windows.Forms.Control.OnClick(EventArgs e)
w System.Windows.Forms.Button.OnClick(EventArgs e)
w System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
w System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
w System.Windows.Forms.Control.WndProc(Message& m)
w System.Windows.Forms.ButtonBase.WndProc(Message& m)
w System.Windows.Forms.Button.WndProc(Message& m)
w System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
w System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
w System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
w System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
w System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
w System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
w System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
w System.Windows.Forms.Application.Run(Form mainForm)
w FilesEncoding.Program.Main() w c:\users\grabarz\documents\visual studio 2010\Projects\FilesEncoding\FilesEncoding\Program.cs:wiersz 18
w System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
w System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
w Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
w System.Threading.ThreadHelper.ThreadStart_Context(Object state)
w System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
w System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
w System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
w System.Threading.ThreadHelper.ThreadStart()
InnerException:

Answer

I'm not sure, is this code correct, but finally it start to work! I've got similar solution, here but I don't know what's are diffrents between constructor in my topic question, and this. In my opinion my first record should work perfectly too. Here's my code:

private string userName;
private string fileDirectory;

public AddFileForm(Files _file) : this(_file.userName, _file.directory) {  }
public AddFileForm(string user, string directory)
{
    userName = user;
    fileDirectory = directory;
    InitializeComponent();
}

private void buttonAdd_Click(object sender, EventArgs e)
{
    userName = listBoxUserList.SelectedItem.ToString();
    fileDirectory = listBoxItems.SelectedItem.ToString();
        try
        {
            Files file = new Files();
            file.userName = userName;
            file.directory = fileDirectory;
            DBConnection connection = new DBConnection();
            connection.AddFile(file);
        }
        catch (Exception)
        {
            MessageBox.Show("Failed database connection!");
        }
    }
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