绑定DateTimePicker控件VS NULL [英] bound DateTimePicker Control VS NULL

问题描述

好的，在数据​​绑定DTP上处理NULL异常的最佳方法是什么？

"没有它是NULL ...这就是为什么我把DTP放在那里所以我可以让它不是NULL！" ...啊

<预类= "prettyprint" 风格= ""> users_dtp_shiftstart.DataBindings.Add（QUOT;值QUOT ;, UsersBind，" ShiftStart"）
users_dtp_shiftend.DataBindings。添加（" value"，UsersBind，" ShiftEnd"）

通常我在包含日期的数据表列上创建默认值，但现在我正在处理一个SQL表，该表具有NULL日期值的现有行。我不能只插入任何日期，如果日期不适用，列需要保持为NULL。

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生活就像你今天要死了一样，学会好像你将要永远活着--Mahatma Gandhi

解决方案

这可能会也可能不会解决null / nothing问题。

 Public类DateTimePickerSpecial 
继承System.Windows.Forms.DateTimePicker 
 
私人oldFormat作为DateTimePickerFormat = DateTimePickerFormat.Short 
私人oldCustomFormat作为字符串=没有
私人bIsNull由于布尔=假
 
公共事件ValueIsNothing（ByVal sender As Boolean）
 
 Public Sub New（）
 MyBase.New（）
 End Sub 
 
 Public Shadows属性值（）As DateTime 
获取
如果bIsNull则
 RaiseEvent ValueIsNothing（bIsNull）
返回DateTime.MinValue 
 Else 
 RaiseEvent ValueIsNothing（bIsNull）
返回MyBase.Value 
结束如果
 
结束获取
设置（ByVal值）作为DateTime）
 
如果value = DateTime.MinValue那么
如果bIsNull = False那么
 oldFormat = Me.Format 
 oldCustomFormat = Me.CustomFormat 
 bIsNull =真
结束如果
 
 Me.Format = DateTimePickerFormat.Custom 
 Me.CustomFormat =" " 
 Else 
如果bIsNull那么
 Me.Format = oldFormat 
 Me.CustomFormat = oldCustomFormat 
 bIsNull = False 
结束如果
 MyBase.Value = value 
结束如果
 RaiseEvent ValueIsNothing（bIsNull）
结束集
结束属性
受保护覆盖​​Sub OnCloseUp（ByVal eventargs As EventArgs）
如果控制。 MouseButtons = MouseButtons.None然后
如果bIsNull那么
 Me.Format = oldFormat 
 Me.CustomFormat = oldCustomFormat 
 bIsNull = False 
结束如果
结束如果
 
的RaiseEvent ValueIsNothing（bIsNull）
 MyBase.OnCloseUp（EventArgs的）
 
结束子
 
受保护的覆盖子的onkeydown（BYVALË作为KeyEventArgs ）
 MyBase.OnKeyDown（e）
 
如果e.KeyCode = Keys.Delete然后
 Me.Value = DateTime.MinValue 
 End if 
 End Sub 
 End Class 

Okay, what is the best way to handle the NULL exception on databound DTP??

"No duh it's NULL... it's why I put the DTP there so I can make it not NULL!" ...ugh

users_dtp_shiftstart.DataBindings.Add("value", UsersBind, "ShiftStart")
users_dtp_shiftend.DataBindings.Add("value", UsersBind, "ShiftEnd")

Normally I create a default value on the datatable columns containing the date, but now I am dealing with a SQL table that has existing rows with NULL date values. I can't just insert any date either, the column needs to remain NULL if the date is not applicable.

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Live as if you were going to die today, learn as if you were going to live forever -Mahatma Gandhi

解决方案

This may or may not assist with the null/nothing issue.

Public Class DateTimePickerSpecial
    Inherits System.Windows.Forms.DateTimePicker

    Private oldFormat As DateTimePickerFormat = DateTimePickerFormat.Short
    Private oldCustomFormat As String = Nothing
    Private bIsNull As Boolean = False

    Public Event ValueIsNothing(ByVal sender As Boolean)

    Public Sub New()
        MyBase.New()
    End Sub

    Public Shadows Property Value() As DateTime
        Get
            If bIsNull Then
                RaiseEvent ValueIsNothing(bIsNull)
                Return DateTime.MinValue
            Else
                RaiseEvent ValueIsNothing(bIsNull)
                Return MyBase.Value
            End If

        End Get
        Set(ByVal value As DateTime)

            If value = DateTime.MinValue Then
                If bIsNull = False Then
                    oldFormat = Me.Format
                    oldCustomFormat = Me.CustomFormat
                    bIsNull = True
                End If

                Me.Format = DateTimePickerFormat.Custom
                Me.CustomFormat = " "
            Else
                If bIsNull Then
                    Me.Format = oldFormat
                    Me.CustomFormat = oldCustomFormat
                    bIsNull = False
                End If
                MyBase.Value = value
            End If
            RaiseEvent ValueIsNothing(bIsNull)
        End Set
    End Property
    Protected Overrides Sub OnCloseUp(ByVal eventargs As EventArgs)
        If Control.MouseButtons = MouseButtons.None Then
            If bIsNull Then
                Me.Format = oldFormat
                Me.CustomFormat = oldCustomFormat
                bIsNull = False
            End If
        End If

        RaiseEvent ValueIsNothing(bIsNull)
        MyBase.OnCloseUp(eventargs)

    End Sub

    Protected Overrides Sub OnKeyDown(ByVal e As KeyEventArgs)
        MyBase.OnKeyDown(e)

        If e.KeyCode = Keys.Delete Then
            Me.Value = DateTime.MinValue
        End If
    End Sub
End Class

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