首先,在一个ActiveX DLL或ActiveX EXE建立一个名为"Persist"的类。这一个类必须是公共的,所以它的实例属性可以有5个。属性Persistable设置为1- Persistable。在类中添加三个事件函数,Class_InitProperties, Class_ReadProperties, and Class_WriteProperties。
在公共声明部分建立一个新的私有变量:
Private cstrMySetting as String
当Class_InitProperties第一次建立时即初始化类中的属性:
Private Sub Class_InitProperties()
cstrMySetting = vbNullString
End Sub
Class_ReadProperties函数可以从一个属性标签中返回一个对象的值:
Private Sub Class_ReadProperties(PropBag As PropertyBag)
cstrMySetting = PropBag.ReadProperty("MySetting",
vbNullString)
End Sub
Class_WriteProperties函数将数值写入到属性标签:
Private Sub Class_WriteProperties(PropBag As PropertyBag)
Call PropBag.WriteProperty("MySetting",
cstrMySetting, _
vbNullString)
End Sub
在每一个属性中,Property Let函数调用PropertyChanged,将把这一属性标记为“dirty”。如果任一属性被标记为“dirty”,Class_WriteProperties函数即被调用,过程如下所示:
Public Property Let MySetting(ByValNewValue As String)
cstrMySetting = NewValue
Call PropertyChanged("MySetting")
End Property
Public Property Get MySetting() As String
MySetting = cstrMySetting
End Property
这个类建立的目的是为了把类中信息赋予PropertyBag。调用PropertyBag中的WriteProperty方法,传递对象,并保存,然后调用ReadProperty重新获取。下面的代码段说明了在程序中如何使用这一过程:
Dim obj As Persist
Dim pb As PropertyBag
Set obj = New Persist
obj.MySetting = "Testing"
Set pb = New PropertyBag
'Save Object
Call pb.WriteProperty("PersistSample", obj)
Set obj = Nothing
'Restore object
Set obj = pb.ReadProperty("PersistSample")
Debug.Printobj.MySetting