一年前，VB中在编制OCX控件时的一点心得，发出来一起共享。

   控件的属性在运行与设计模式切换时，属性值为丢失，可以要用WriteProperties来保存属性值，再用ReadProperties读取，具体情况如下：

   1、在设计模式往运行模式切换时，先用WriteProperties保存属性值，由于在运行时要使用该值，所以用ReadProperties读出。

   2、在结速运行状态切换到设计模式时，不需要保存控件在运行状态的值，所以不调用WriteProperties保存，而直接读取程序员在设计模式下的值。

   3、WriteProperties及ReadProperties事件只在设计调试中有效，编译为EXE文件后不再有效。此两事件及PropBag对象只是为了方便设计而存在。

例程：

'本控件是text与updown控件的结合，使用updown改变数据值
'也可手工改变text值

Dim m_UpMax As Long
Dim m_DownMin As Long
Dim m_value As Long
Dim m_Enabled As Boolean

Private Sub Text1_Change()
On Error GoTo Err
Dim txti As Long

'txti用来零时保存text1值
txti = CLng(text1.Text)
If txti > UpDown1.Max Then
    text1.Text = UpDown1.Max
End If
If txti < UpDown1.Min Then
    text1.Text = UpDown1.Min
End If
txti = CLng(text1.Text)
UpDown1.value = txti
Exit Sub

Err:
text1.Text = UpDown1.value
End Sub

Private Sub UpDown1_Change()
text1.Text = UpDown1.value
End Sub

Private Sub UserControl_Resize()
On Error Resume Next
Dim t As Long
Dim b As Long
t = UserControl.Width - UpDown1.Width
b = UserControl.Height - 1
text1.Width = t
text1.Height = b
text1.Move 0, 0
UpDown1.Move t, 0
UpDown1.Height = b
End Sub

Public Property Get UpMax() As Long
UpMax = m_UpMax
End Property

Public Property Let UpMax(ByVal vNewvalue As Long)
m_UpMax = vNewvalue
UpDown1.Max = m_UpMax
PropertyChanged "UpMax"
End Property

Public Property Get DownMin() As Long
DownMin = m_DownMin
End Property

Public Property Let DownMin(ByVal vNewvalue As Long)
m_DownMin = vNewvalue
UpDown1.Min = vNewvalue
PropertyChanged "DownMin"
End Property

Private Sub UserControl_WriteProperties(PropBag As PropertyBag)
Call PropBag.WriteProperty("UpMax", m_UpMax, 0)
Call PropBag.WriteProperty("DownMin", m_DownMin, 0)
Call PropBag.WriteProperty("value", CLng(text1.Text), 0)
Call PropBag.WriteProperty("Enabled", m_Enabled, True)
End Sub

Private Sub UserControl_ReadProperties(PropBag As PropertyBag)
'使用PropBag.ReadProperty时一定要有默认值，否则如果没有在设计时改变过属性值（
'即没有使用writeProperty保存属性值）就无法读取，会产生“运行时错误”

m_UpMax = PropBag.ReadProperty("UpMax", 0)
m_DownMin = PropBag.ReadProperty("DownMin", 0)
m_value = PropBag.ReadProperty("value", 0)
m_Enabled = PropBag.ReadProperty("Enabled", True)
UpDown1.Max = m_UpMax
UpDown1.Min = m_DownMin
UpDown1.value = m_value
UpDown1.Enabled = m_Enabled
text1.Text = m_value
text1.Enabled = m_Enabled
End Sub

Public Property Get value() As Long
Attribute value.VB_UserMemId = 0
m_value = CLng(text1.Text)
value = m_value
End Property

Public Property Let value(ByVal vNewvalue As Long)
If vNewvalue > m_UpMax Then
    m_value = m_UpMax
ElseIf vNewvalue < m_DownMin Then
    m_value = m_DownMin
Else
    m_value = vNewvalue
End If
text1.Text = m_value

PropertyChanged "value"
End Property

Public Property Get Enabled() As Boolean
Enabled = m_Enabled
End Property

Public Property Let Enabled(ByVal vNewvalue As Boolean)
m_Enabled = vNewvalue
UpDown1.Enabled = m_Enabled
text1.Enabled = m_Enabled
PropertyChanged "Enabled"
End Property