如果未选择日期,如何设置datetimepicker为空值(c#winforms)

Question

Binding b = new Binding( "Value", person, "BdayNullable", true );
dtBirthdayNullable.DataBindings.Add( b );
b.Format += new ConvertEventHandler( dtBirthdayNullable_Format );

b.Parse += new ConvertEventHandler( dtBirthdayNullable_Parse );

void dtBirthdayNullable_Format( object sender, ConvertEventArgs e )
{
    // e.Value is the object value, we format it to be what we want to show up in the control

    Binding b = sender as Binding;
    if ( b != null )
    {
        DateTimePicker dtp = (b.Control as DateTimePicker);
        if ( dtp != null )
        {
            if ( e.Value == DBvalue.value )
            {
                dtp.ShowCheckBox = true;
                dtp.Checked = false;

                // have to set e.Value to SOMETHING, since it's coming in as NULL
                // if i set to DateTime.Today, and that's DIFFERENT than the control's current 
                // value, then it triggers a CHANGE to the value, which CHECKS the box (not ok)
                // the trick - set e.Value to whatever value the control currently has.  
                // This does NOT cause a CHANGE, and the checkbox stays OFF.
                e.Value = dtp.Value;    
            }
            else
            {
                dtp.ShowCheckBox = true;
                dtp.Checked = true;
                // leave e.Value unchanged - it's not null, so the DTP is fine with it.
            }
        }
    }
}
void dtBirthdayNullable_Parse( object sender, ConvertEventArgs e )
{
    // e.value is the formatted value coming from the control.  
    // we change it to be the value we want to stuff in the object.

    Binding b = sender as Binding;
    if ( b != null )
    {
        DateTimePicker dtp = (b.Control as DateTimePicker);
        if ( dtp != null )
        {
            if ( dtp.Checked == false )
            {
                dtp.ShowCheckBox = true;
                dtp.Checked = false;
                e.Value = DBvalue.Value
            }
            else
            {
                DateTime val = Convert.ToDateTime( e.Value );
                e.Value =val;
            }
        }
    }
}

---

编辑

我找到了一个很好的解决方案

http://blogs.interknowlogy.com/danhanan/archive/2007/01/21/10847.aspx

另一个完美的解决方案

http://www.mofeel.net/70-microsoft-public-dotnet-framework-windowsforms/8806.aspx

Answer 1

DateTimePickers不能设置为null,因为DateTime不能为null,但您可以将它们DateTime.MinValue设置为未初始化的默认值DateTime.然后你只是检查是否dtp.Value = DateTime.MinValue,如果是,将其视为null.

但是,如果您想真正区分何时没有选择任何值,最简单的方法是设置DateTimePicker.ShowCheckBox为true,然后检查dtp.Checked是否为真,您将读取该值,否则将其视为null.

Answer 2

您可以检查绑定源是否提供"空日期"或您不想显示的日期值.

如果是,请选择自定义格式:

yourDTP.Format = DateTimePickerFormat.Custom
yourDTP.CustomFormat = " "

添加"CloseUp"或"ValueChanged"事件处理程序以重置用户操作的格式:

yourDTP.Format = DateTimePickerFormat.Short