Question

If i run this code the application will crash, and i dont understand why,
it seemes to me its a bug – or is it?

Steps: place a System.Windows.Forms.DataGridView on a form.

Define a datasource class:

     public class SomeClass
    {
       public SomeClass()
       {
         col1 = string.Empty;
         Col2= string.Empty;
       }
        public string col1 {get;set;}
        public string Col2 { get; set; }
    }

//Declare new. (0 elements)
private List<SomeClass> _col = new List<SomeClass>();

//First run this

      private void button1_Click(object sender, EventArgs e)
    {
        dataGridView1.DataSource = null;
        dataGridView1.DataSource = _col;
    }

//Then run this

      private void button2_Click(object sender, EventArgs e)
    {
        _col.Add(new SomeClass() { col1 = "Value1", Col2 = "Value2"  });

        dataGridView1.DataSource = null;
        dataGridView1.DataSource = _col;
    }

//If you now click in the grid it will crash.

//Note-if i dont set null - it will not be update, if i only run button2 several times
//it works fine !

Exception:

Blockquote
System.IndexOutOfRangeException was unhandled
Message=Index -1 does not have a value.
Source=System.Windows.Forms
StackTrace:
at System.Windows.Forms.CurrencyManager.get_Item(Int32 index)
at System.Windows.Forms.CurrencyManager.get_Current()
at System.Windows.Forms.DataGridView.DataGridViewDataConnection.OnRowEnter(DataGridViewCellEventArgs e)
at System.Windows.Forms.DataGridView.OnRowEnter(DataGridViewCell& dataGridViewCell, Int32 columnIndex, Int32 rowIndex, Boolean canCreateNewRow, Boolean validationFailureOccurred)
at System.Windows.Forms.DataGridView.SetCurrentCellAddressCore(Int32 columnIndex, Int32 rowIndex, Boolean setAnchorCellAddress, Boolean validateCurrentCell, Boolean throughMouseClick)
at System.Windows.Forms.DataGridView.OnCellMouseDown(HitTestInfo hti, Boolean isShiftDown, Boolean isControlDown)
at System.Windows.Forms.DataGridView.OnCellMouseDown(DataGridViewCellMouseEventArgs e)
at System.Windows.Forms.DataGridView.OnMouseDown(MouseEventArgs e)
at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)
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(Form mainForm)
at WindowsFormsApplication3.Program.Main() in C:\TestUtveckling\WindowsFormsApplication3\WindowsFormsApplication3\Program.cs:line 18
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException:

If i dont run the first step, connecting the 0 elements to the datasource,
it works. I say its a bug in the DataGridView ! Or is it something else?

Answer 1

Why do you keep setting DataSource? Usually, you should only set DataSource once and it will keep track of changes like adding, removing, modifying. If it does not, use a BindingSource as the data source for the DataGridView and the list as the data source for the BindingSource and call BindingSource.RefreshBindings upon changes.

Not every exception is the source of a bug in the framework 🙂