DataGridView in TabControl and CellValidating lead to problems

I created a little form with a TabControl on it and a combobox.

On the  first page i added a DataGridView with 2 columns, not bound to any data (data entered directly).

Also, for the grid i added an event handler for CellValidating in which i test if the data from the first row is numeric, if not i show a message box with an error and return e.Cancel = true so the DataGridView maintains focus.

Now, if i do the following :

1 - edit cell on first column and enter a wrong value (a text)

2 - click on TabControl to change to the other tab page, error is shown that the value is not correct, close the error

3 - modify the value to be correct (enter a number)

4 - change to any of the other cells in the DataGridView and try to edit them with the mouse (double click to edit), it just doesn't work.

The only solution to "fix" this is to change to the other tabPage on the TabControl and back, this way the DataGridView regains its ability to edit cells with the mouse.

Is there any solution to this ?

Note: If i don't show the message box in the CellValidating function then the problem doesn't occur. I know i could show an errormessage on the row of the column, but the application i'm writing requires that i display messageboxes for all errors (and i can't make the grid work differently from all other controls on the other dialogs just because of this bug).

So, is there any way to fix this ?

Here's my code (at least the part that relates to the problem)

 public Form1()
        {
            InitializeComponent();  
 
            // add some data to the grid so it's not empty  
 
            // first row
            DataGridViewRow row = new DataGridViewRow();
            DataGridViewTextBoxCell value = new DataGridViewTextBoxCell();
            DataGridViewTextBoxCell text = new DataGridViewTextBoxCell();
            value.Value = "12";
            text.Value = "some text";  
 
            row.Cells.Add(value);
            row.Cells.Add(text);  
 
            dataGridView1.Rows.Add(row);  
 
            // second row
            row = new DataGridViewRow();
            value = new DataGridViewTextBoxCell();
            text = new DataGridViewTextBoxCell();
            value.Value = "1000";
            text.Value = "another text";  
 
            row.Cells.Add(value);
            row.Cells.Add(text);  
 
            dataGridView1.Rows.Add(row);
        }  
 
private void dataGridView1_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
        {
            // first row must be numeric value
            if (e.ColumnIndex == 0)
            {
                try
                {
                    double x = Convert.ToDouble(e.FormattedValue);
                }
                catch (System.Exception ex)
                {
                    MessageBox.Show("Error, value is not a double");
                    // if we can't convert then bail out
                    e.Cancel = true;
                }
            }
        }  
 
...
private void InitializeComponent()
        {
...
this.dataGridView1.CellValidating += new System.Windows.Forms.DataGridViewCellValidatingEventHandler(this.dataGridView1_CellValidating);
...
}

该问题源自MSDN Bug

http://social.msdn.microsoft.com/Forums/windows/en-US/c3634471-49cb-4274-afa4-c4bcd184b52c/datagridview-in-tabcontrol-and-cellvalidating-lead-to-problems

如果觉得英文不爽，这有这个问题的中文版

http://bbs.csdn.net/topics/390492161?page=1#post-394804656

下面是我对这个问题的规避方法

首先确定问题是在切换页签引发的校验中，弹出弹窗，导致焦点失去，从而致使datagridview Cell无法再进入编辑模式。

所以可以通过在校验过程弹窗后，重新fouce。

  private void dataGridView1_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
        {if(e.ColumnIndex==-||e.RowIndex==-)
            {
                return;
            }
            if(string.IsNullOrEmpty(e.FormattedValue.ToString()))
            {
                return;
            }
            int tempValue = -;
            if(!int.TryParse(e.FormattedValue.ToString(),out tempValue))
            {
                MessageBox.Show("Erro Data.");
                dataGridView1.Focus();
                e.Cancel = true;
                dataGridView1.CancelEdit();
            }
        }

但是fouce后会导致tab页签发生切换，而不是我们想要的留在该页签（这里是因为焦点重获得，导致某个标志位值被修改，tabControl未进入留在本页签的代码分支），所以需要为tabControl写Deselecting事件来“要求停留在本页签”，这里需要一个标志位，来实现如果校验通过，那么页签正常切换，如果失败不能切换。

  private void dataGridView1_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
        {
            m_IsInvalid = false;
            if(e.ColumnIndex==-||e.RowIndex==-)
            {
                return;
            }
            if(string.IsNullOrEmpty(e.FormattedValue.ToString()))
            {
                return;
            }
            int tempValue = -;
            if(!int.TryParse(e.FormattedValue.ToString(),out tempValue))
            {
                MessageBox.Show("Erro Data.");
                dataGridView1.Focus();
                e.Cancel = true;
                m_IsInvalid = true;
                dataGridView1.CancelEdit();
            }
        }

 private void tabControl1_Deselecting(object sender, TabControlCancelEventArgs e)
        {
            if (e.TabPage == tabPage2)
            {
                if (m_IsInvalid)
                {
                    e.Cancel = true;
                }
            }
        }

 private void dataGridView1_RowValidating(object sender, DataGridViewCellCancelEventArgs e)
        {
            m_IsInvalid = false;
            if (e.ColumnIndex == - || e.RowIndex == -)
            {
                return;
            }
            MessageBox.Show("Erro Data.");
            dataGridView1.Focus();
            e.Cancel = true;
            m_IsInvalid = true;
            dataGridView1.CancelEdit();
        }

这样就规避了页签切换校验失败，导致无法点击鼠标编辑datagridview cell的问题。

当然，坑一般是连着的，datagridview的CausesValidation一旦设为true，那么就是一旦焦点失去，它就触发校验，这样用户体验感非常差

想想看，我表格填错了，想直接点cancel取消掉，都要各种弹窗，无法正常Cancel。所以我们一般做了这样的策略
就是如果是在表格内进行操作，那么焦点失去立即校验。如果是在表格外，那么取消这一坑爹设定。

  private void dataGridView1_MouseLeave(object sender, EventArgs e)
        {
            dataGridView1.CausesValidation = false;
        }
 
        private void dataGridView1_MouseEnter(object sender, EventArgs e)
        {
            dataGridView1.CausesValidation = true;
        }

好，这样，我们的Cancel，关闭窗体的X，就能正常运作了。

但是，但是。。。。我们发现页签切换点击，也是在表格外，这样就会导致页签切换时，触发一个行校验后，再点击页签切换，就不会触发表格校验，同时因为我们之前设置的全局变量导致页签一直无法切换，也没有提示。

我们必须在点击页签切换时，将dataGridView1.CausesValidation从false重新赋值为true。很悲剧的是，这样的事件微软没有给出。所以必须要重写下tabControl控件

  public class CustomTabControl:TabControl
    {
        public event EventHandler<CancelEventArgs> PreClicked;
 
        protected override void WndProc(ref Message m)
        {
            if (m.Msg == )
            {
                var cancelArg = new CancelEventArgs(false);
                OnPreClicked(cancelArg);
                if (cancelArg.Cancel)
                {
                    return;
                }
            }
            base.WndProc(ref m);
        }
        private void OnPreClicked(CancelEventArgs e)
        {
            var handler = PreClicked;
            if(handler!=null)
            {
                handler(this,e );
            }
        }
    }

Form1窗体：

 private void tabControl1_PreClicked(object sender, CancelEventArgs e)
        {
            dataGridView1.CausesValidation = true;
        }

这样所有就能按照设计正常运行了。

这是Demo代码