c# - 如果未选择日期，如何将 datetimepicker 设置为空值 (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;
            }
        }
    }
}

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编辑

我在这里找到了一个很好的解决方案

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

这里是另一个完美的解决方案

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

Answer 1

DateTimePicker 不能设置为空，因为 DateTime 不能为空，但您可以将它们设置为 DateTime.MinValue这是未初始化的 DateTime 的默认值。然后您只需检查 dtp.Value = DateTime.MinValue 是否存在，如果是，则将其视为 null。

但是，如果你想在没有选择值时真正区分，最简单的方法是将DateTimePicker.ShowCheckBox设置为true，然后检查dtp.Checked 如果为真，则读取该值，否则将其视为 null。