Idatagridvieweditingcontrol的问题,进行值的程序更改后并不显示其更改后的值

Question

以下代码摘自VS2005中的文档,中间中文注释处即为问题using System;
using System.Windows.Forms;public class CalendarColumn : DataGridViewColumn
{
    public CalendarColumn() : base(new CalendarCell())
    {
    }    public override DataGridViewCell CellTemplate
    {
        get
        {
            return base.CellTemplate;
        }
        set
        {
            // Ensure that the cell used for the template is a CalendarCell.
            if (value != null && 
                !value.GetType().IsAssignableFrom(typeof(CalendarCell)))
            {
                throw new InvalidCastException("Must be a CalendarCell");
            }
            base.CellTemplate = value;
        }
    }
}public class CalendarCell : DataGridViewTextBoxCell
{    public CalendarCell()
        : base()
    {
        // Use the short date format.
        this.Style.Format = "d";
    }    public override void InitializeEditingControl(int rowIndex, object 
        initialFormattedValue, DataGridViewCellStyle dataGridViewCellStyle)
    {
        // Set the value of the editing control to the current cell value.
        base.InitializeEditingControl(rowIndex, initialFormattedValue, 
            dataGridViewCellStyle);
        CalendarEditingControl ctl = 
            DataGridView.EditingControl as CalendarEditingControl;
        ctl.Value = (DateTime)this.Value;
    }    public override Type EditType
    {
        get
        {
            // Return the type of the editing contol that CalendarCell uses.
            return typeof(CalendarEditingControl);
        }
    }    public override Type ValueType
    {
        get
        {
            // Return the type of the value that CalendarCell contains.
            return typeof(DateTime);
        }
    }    public override object DefaultNewRowValue
    {
        get
        {
            // Use the current date and time as the default value.
            return DateTime.Now;
        }
    }
}class CalendarEditingControl : DateTimePicker, IDataGridViewEditingControl
{
    DataGridView dataGridView;
    private bool valueChanged = false;
    int rowIndex;    public CalendarEditingControl()
    {
        this.Format = DateTimePickerFormat.Short;
    }    // Implements the IDataGridViewEditingControl.EditingControlFormattedValue 
    // property.
    public object EditingControlFormattedValue
    {
        get
        {
            return this.Value.ToShortDateString();
        }
        set
        {
            String newValue = value as String;
            if (newValue != null)
            {
                this.Value = DateTime.Parse(newValue);
            }
        }
    }    // Implements the 
    // IDataGridViewEditingControl.GetEditingControlFormattedValue method.
    public object GetEditingControlFormattedValue(
        DataGridViewDataErrorContexts context)
    {
        return EditingControlFormattedValue;
    }    // Implements the 
    // IDataGridViewEditingControl.ApplyCellStyleToEditingControl method.
    public void ApplyCellStyleToEditingControl(
        DataGridViewCellStyle dataGridViewCellStyle)
    {
        this.Font = dataGridViewCellStyle.Font;
        this.CalendarForeColor = dataGridViewCellStyle.ForeColor;
        this.CalendarMonthBackground = dataGridViewCellStyle.BackColor;
    }    // Implements the IDataGridViewEditingControl.EditingControlRowIndex 
    // property.
    public int EditingControlRowIndex
    {
        get
        {
            return rowIndex;
        }
        set
        {
            rowIndex = value;
        }
    }    // Implements the IDataGridViewEditingControl.EditingControlWantsInputKey 
    // method.
    public bool EditingControlWantsInputKey(
        Keys key, bool dataGridViewWantsInputKey)
    {
        // Let the DateTimePicker handle the keys listed.
        switch (key & Keys.KeyCode)
        {
            case Keys.Left:
            case Keys.Up:
            case Keys.Down:
            case Keys.Right:
            case Keys.Home:
            case Keys.End:
            case Keys.PageDown:
            case Keys.PageUp:
                return true;
            default:
                return false;
        }
    }    // Implements the IDataGridViewEditingControl.PrepareEditingControlForEdit 
    // method.
    public void PrepareEditingControlForEdit(bool selectAll)
    {
        // No preparation needs to be done.
    }    // Implements the IDataGridViewEditingControl
    // .RepositionEditingControlOnValueChange property.
    public bool RepositionEditingControlOnValueChange
    {
        get
        {
            return false;
        }
    }    // Implements the IDataGridViewEditingControl
    // .EditingControlDataGridView property.
    public DataGridView EditingControlDataGridView
    {
        get
        {
            return dataGridView;
        }
        set
        {
            dataGridView = value;
        }
    }    // Implements the IDataGridViewEditingControl
    // .EditingControlValueChanged property.
    public bool EditingControlValueChanged
    {
        get
        {
            return valueChanged;
        }
        set
        {
            valueChanged = value;
        }
    }    // Implements the IDataGridViewEditingControl
    // .EditingPanelCursor property.
    public Cursor EditingPanelCursor
    {
        get
        {
            return base.Cursor;
        }
    }    protected override void OnValueChanged(EventArgs eventargs)
    {
        // Notify the DataGridView that the contents of the cell
        // have changed.
        valueChanged = true;
        this.EditingControlDataGridView.NotifyCurrentCellDirty(true);
        base.OnValueChanged(eventargs);
    }
    //此处为文档示例外的代码,为了约束输入,如果输入的日期大于当前日期则将其更改为当前日期
     //经过测试,如使用键盘输入后并按回车后,单元格的日期并不会象程序逻辑那样进行更改,但是下面的代码确实是执行了一次!
     //如果使用执鼠标进行选择操作,则会更改
     //就此处不知道如何更改以达到逻辑目标:输入的日期大于当前日期则将其更改为当前日期
    protected override void OnValidating(System.ComponentModel.CancelEventArgs e)
    {
        base.OnValidating(e);
        if (this.Value > DateTime.Now.Date)
        {
            this.Value = DateTime.Now.Date;
        }
    }
}public class Form1 : Form
{
    private DataGridView dataGridView1 = new DataGridView();    [STAThreadAttribute()]
    public static void Main()
    {
        Application.Run(new Form1());
    }    public Form1()
    {
        this.dataGridView1.Dock = DockStyle.Fill;
        this.Controls.Add(this.dataGridView1);
        this.Load += new EventHandler(Form1_Load);
        this.Text = "DataGridView calendar column demo";
    }    private void Form1_Load(object sender, EventArgs e)
    {
        CalendarColumn col = new CalendarColumn();
        this.dataGridView1.Columns.Add(col);
        this.dataGridView1.RowCount = 5;
        foreach (DataGridViewRow row in this.dataGridView1.Rows)
        {
            row.Cells[0].Value = DateTime.Now;
        }
    }
}

Answer 1

When finish keyboard editing,
tracing shows that the CalendarCell asks the CalendarEditingControl for display value before calling the validation.A quick workaround would be updating the CalendarCell after the validation://此处为文档示例外的代码,为了约束输入,如果输入的日期大于当前日期则将其更改为当前日期
    protected override void OnValidating(System.ComponentModel.CancelEventArgs e)
    {
        base.OnValidating(e);
        if (this.Value > DateTime.Now.Date)
        {
            this.Value = DateTime.Now.Date;
            dataGridView.CurrentCell.Value = this.Value;         //<------
        }
    }

Answer 2

No, it is not correct. The update you saw is triggered by some other event. Try this:1. comment out the added line - dataGridView.CurrentCell.Value = this.Value;
2. use mouse to select a date
3. use tab to move to next row, you will the wrong behaviour as in the keyboard editing cases.
I suspect the update is triggered by mouse click which asks each row for a value to display...