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POWhy do i get this NullReferenceExeption c#
 

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  1. POWhy do i get this NullReferenceExeption c#
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    <p>Good night, I've been working in some codes for an aplication to manage connected users and Equipments via Active directory queries....</p> <p>Then I get this error "NullReferenceException was unhandled" for about a week, working with the code this is the only thing stopping the application now.</p> <p>Can any one help me with this...</p> <p>And this is the code of the background worked i used...</p> <pre><code> `private void backgroundWorker2_Dowork(object sender, DoWorkEventArgs e) { try { e.Result = ""; int val = 6000; for (int a = 1; a &lt;= val; a++) { counter.Text = Convert.ToString(a); if (txtWorkGroupName.Text == "") return; DataTable dt = new DataTable(); dt.Clear(); dt.Columns.Add(new DataColumn("ComputerName", typeof(String))); //0 dt.Columns.Add(new DataColumn("IP", typeof(String))); //1 dt.Columns.Add(new DataColumn("MAC", typeof(String))); //2 dt.Columns.Add(new DataColumn("Descubierto", typeof(String))); //3 //int i = 0; try { // Datos del grupo WinNT://&amp;&amp;&amp;&amp;(Nombre del grupo de trabajo) DirectoryEntry DomainEntry = new DirectoryEntry("WinNT://" + txtWorkGroupName.Text + ""); DomainEntry.Children.SchemaFilter.Add("Computer"); ///************************************************* /// Interacting with pc's in the domain ///************************************************* foreach (DirectoryEntry machine in DomainEntry.Children) { string strMachineName = machine.Name; string strMACAddress = ""; IPAddress IPAddress; DateTime discovered; try { IPAddress = getIPByName(machine.Name); } catch { continue; }//try/catch ///************************************************* /// Get Mac ///************************************************* strMACAddress = getMACAddress(IPAddress); discovered = DateTime.Now; ///************************************************* /// Add lines in the grid ///************************************************* DataRow dr = dt.NewRow(); dr[0] = machine.Name; dr[1] = IPAddress; dr[2] = strMACAddress; dr[3] = Convert.ToString(discovered); dt.Rows.Add(dr); ///************************************************* /// SETTING DATASOURCE ///************************************************* dgvComputers1.DataSource = dt; Thread.Sleep(2000); }//foreach loop catch (Exception ex) { { MessageBox.Show(ex.Message); } } if (backgroundWorker2.CancellationPending) { e.Cancel = true; return; } } } catch (NullReferenceException ex) { MessageBox.Show("error:" + ex); } catch (NoNullAllowedException ex) { MessageBox.Show("error:" + ex); } catch (AccessViolationException ex) { MessageBox.Show("error:" + ex); } } ` </code></pre> <p>This is the exeption details, sorry that they are in spanish. </p> <p><code> System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="System.Windows.Forms" StackTrace: en System.Windows.Forms.DataGridViewRowHeaderCell.PaintPrivate(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates dataGridViewElementState, Object formattedValue, String errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts, Boolean computeContentBounds, Boolean computeErrorIconBounds, Boolean paint) en System.Windows.Forms.DataGridViewRowHeaderCell.Paint(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, Object value, Object formattedValue, String errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts) en System.Windows.Forms.DataGridViewCell.PaintWork(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts) en System.Windows.Forms.DataGridViewRow.PaintHeader(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow, DataGridViewPaintParts paintParts) en System.Windows.Forms.DataGridViewRow.Paint(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow) en System.Windows.Forms.DataGridView.PaintRows(Graphics g, Rectangle boundingRect, Rectangle clipRect, Boolean singleHorizontalBorderAdded) en System.Windows.Forms.DataGridView.PaintGrid(Graphics g, Rectangle gridBounds, Rectangle clipRect, Boolean singleVerticalBorderAdded, Boolean singleHorizontalBorderAdded) en System.Windows.Forms.DataGridView.OnPaint(PaintEventArgs e) en System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs) en System.Windows.Forms.Control.WmPaint(Message&amp; m) en System.Windows.Forms.Control.WndProc(Message&amp; m) en System.Windows.Forms.DataGridView.WndProc(Message&amp; m) en System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&amp; m) en System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&amp; m) en System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) en System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG&amp; msg) en System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods. IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData) en System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) en System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) en System.Windows.Forms.Application.Run(Form mainForm) en NetworkScanner.Program.Main() en C:\Project Sigma 6\New Power move\discover\Program.cs:línea 17 en System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) en System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) en Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() en System.Threading.ThreadHelper.ThreadStart_Context(Object state) en System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) en System.Threading.ThreadHelper.ThreadStart()</code></p>
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    1. USLuis Nuesi Tejada
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    3. VO
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      1. POWhy do i get this NullReferenceExeption c#
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    1. COI am not sure why this question has been downvoted so badly. Would anyone care to leave a comment? I mean, obviously, the OP is somewhat, eh, formatting-challenged, and english-challenged, but haven't we all seen worse?
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      1. POWhy do i get this NullReferenceExeption c#
      1. USMike Nakis
    2. COWhat returns this java style function `getIPByName(machine.Name);`? null? Or does it throw exception?
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      1. POWhy do i get this NullReferenceExeption c#
      1. USL.B
    3. CO@OP - Please debug through your code and show us the specific line this is occurring on.
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      1. POWhy do i get this NullReferenceExeption c#
      1. USStefan H
 

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