VB.NET - NullReferenceException未處理

Question

通常我自己處理我的錯誤，但這次我需要專家的幫助！ 這從來沒有發生在我身上，並且數據越少（通常）越少，你可以說發生了什麼。

我想寫一個簡單的查詢分析器。我隨機收到這些類型的崩潰：

1）我開始用下面的函數：

Dim thd As New Thread(AddressOf StartSub) 
thd.Start() 

那麼Startsub如下：

Public Sub StartSub() 
    CheckForIllegalCrossThreadCalls = False 
    txtExecution.Text = "Executing query..." 
    Dim query As String = QueryBuilder() 
    UpdateView(query) 
End Sub 

，然後更新視圖更新數據網格我有：

Dim da As New SqlCeDataAdapter(query, connStr) 
    Dim dt As New DataTable() 
    Try 
     da.Fill(dt) 
     txtExecution.Text = "Query executed successfully." 
     dgTickets.DataSource = dt 
    Catch ex As Exception 
     txtExecution.Text = "Query failed." 
     tbGrid.BeginInvoke(Sub() tbGrid.SelectedTab = tbGrid.TabPages(1)) 
    End Try 

2）代碼在UpdateQuery中崩潰在以下李NE（調試不說，它崩潰這裏，我猜對了選擇所有線路，並通過它通過1 1去）：

dgTickets.DataSource = dt 

3）什麼調試器說： 的NullReferenceException是未處理的（...） 使用new關鍵字來創建一個對象實例

堆棧跟蹤：

at System.Windows.Forms.DataGridViewCell.GetEditedFormattedValue(Object value, Int32 rowIndex, DataGridViewCellStyle& dataGridViewCellStyle, DataGridViewDataErrorContexts context) 
    at System.Windows.Forms.DataGridViewCell.PaintWork(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts) 
    at System.Windows.Forms.DataGridViewRow.PaintCells(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow, DataGridViewPaintParts paintParts) 
    at System.Windows.Forms.DataGridViewRow.Paint(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow) 
    at System.Windows.Forms.DataGridView.PaintRows(Graphics g, Rectangle boundingRect, Rectangle clipRect, Boolean singleHorizontalBorderAdded) 
    at System.Windows.Forms.DataGridView.PaintGrid(Graphics g, Rectangle gridBounds, Rectangle clipRect, Boolean singleVerticalBorderAdded, Boolean singleHorizontalBorderAdded) 
    at System.Windows.Forms.DataGridView.OnPaint(PaintEventArgs e) 
    at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer) 
    at System.Windows.Forms.Control.WmPaint(Message& m) 
    at System.Windows.Forms.Control.WndProc(Message& m) 
    at System.Windows.Forms.DataGridView.WndProc(Message& m) 
    at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) 
    at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) 
    at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) 
    at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) 
    at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) 
    at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) 
    at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) 
    at System.Windows.Forms.Application.Run(ApplicationContext context) 
    at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun() 
    at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel() 
    at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine) 
    at SQLquery.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81 

這是相當模糊的實際。上面指定的文件不存在。崩潰的地方用Try-End Try包裝。此外，是的，我已經設置了繪畫事件，但它不應該關注它（或者它可能會這樣做？）。

我真的很感激任何提示，只要這一個。我必須補充一點，我使用visual basic express版本。這個錯誤會偶然發生 - 有時當我幸運的時候什麼也沒有發生，而當我不幸的時候我會發生這種崩潰。

皮特。

Answer 1

你不應該觸摸/更新後臺線程中的任何GUI控件。所以線路喜歡：

txtExecution.Text = "Executing query..." 

和

dgTickets.DataSource = dt 

後臺線程內，是註定要失敗的。這應該始終在主GUI線程上使用Control.BeginInvoke完成。

，你似乎是在做正確

唯一的GUI更新此tbGrid在catch：

tbGrid.BeginInvoke(Sub() tbGrid.SelectedTab = tbGrid.TabPages(1)) 

你應該閱讀有關UI WinForms thread invokes。