如何在没有选择的日期设置的DateTimePicker与空值（C＃的WinForms）

问题描述

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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修改

我发现了一个很好的解决方案在这里

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EDIT

i found a good solution here

下面另一个完美的解决方案。

another perfect solution here

的

推荐答案

的DateTimePicker s不能是设置为null，因为的DateTime 不能为null，但你可以将其设置为 DateTime.MinValue 这是默认对于未初始化值的DateTime 。然后你只检查是否 dtp.Value = DateTime.MinValue ，如果是这样，把它当作空。

DateTimePickers can't be set to null because DateTime can't be null, but you can set them to DateTime.MinValue which is the default value for an uninitialized DateTime. And then you just check if the dtp.Value = DateTime.MinValue and if so, treat it as null.

不过，如果你想在没有价值已被选中，真正区分开来，最简单的方法是设置 DateTimePicker.ShowCheckBox 为true，然后检查 dtp.Checked ，如果这是真的，你读的价值，否则你把它当作一个空。

However, if you want to really distinguish when no value has been selected, the easiest way is to set DateTimePicker.ShowCheckBox to true, and then you check dtp.Checked and if it's true, you read the value, otherwise you treat it as a null.

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