我观察到VB.net中的一个行为,在这个行为中,属性设置者被调用的次数似乎比看起来需要的多,并且调用了姐姐setter方法。为什么Property Setter会比预期更频繁地被调用?
Public Class Form1
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Console.WriteLine("Calling WorkReferenceTypeByReference")
WorkReferenceTypeByReference(ReferenceTypeData)
Console.WriteLine("Called WorkReferenceTypeByReference")
Console.WriteLine("Calling WorkReferenceTypeByValue")
WorkReferenceTypeByValue(ReferenceTypeData)
Console.WriteLine("Called WorkReferenceTypeByValue")
End Sub
Public Sub WorkReferenceTypeByReference(ByRef ref As Point)
Dim b As Point = New Point(4, 4) + ref
Console.WriteLine(" adding (4,4) to " & ref.ToString)
End Sub
Public Sub WorkReferenceTypeByValue(ByVal ref As Point)
Dim b As Point = New Point(4, 4) + ref
Console.WriteLine(" adding (4,4) to " & ref.ToString)
End Sub
Private m_ReferenceType As Point = New Point(0, 0)
Public Property ReferenceTypeData As Point
Get
Console.WriteLine(" Calling ReferenceTypeData getter")
Console.WriteLine(" returning: " & m_ReferenceType.ToString)
Return m_ReferenceType
End Get
Set(ByVal value As Point)
Console.WriteLine(" Calling ReferenceTypeData setter")
Console.WriteLine(" value = " & value.ToString)
m_ReferenceType = value
End Set
End Property
End Class
前面的代码返回到控制台下面的输出
Calling WorkReferenceTypeByReference
Calling ReferenceTypeData getter
returning: {X=0,Y=0}
adding (4,4) to {X=0,Y=0}
Calling ReferenceTypeData setter
value = {X=0,Y=0}
Called WorkReferenceTypeByReference
Calling WorkReferenceTypeByValue
Calling ReferenceTypeData getter
returning: {X=0,Y=0}
adding (4,4) to {X=0,Y=0}
Called WorkReferenceTypeByValue
注意方法执行下列虚假调用属性setter。我认为这种行为是作为一种安全措施产生的,以防止无意中修改基础财产,尽管这可能是意图。
ByRef vs ByVal使用情况下的这种行为很容易通过选择适当的ByVal关键字来解决,然而他们最近注意到了一个更危险的行为,一个导致了重复调用的堆栈溢出,因为setter调用会更新只有调用getter的值。
Public Sub DoSomething()
Dim a As New CustomObject(anotherObject.AProperty(getterArgument))
End Sub
Public Class AnotherObject
Public Property AProperty as SomeType
Get
' Get value
End Get
Set
' Set value, call DoSomething
End Set
End Property
End Class
在前面的例子中,主叫DoSomething的()将触发AProperty吸气剂的方法,但那时,在使用后,将火setter方法,其通过程序逻辑()再次调用DoSomething的。这是对二传手的自动调用令我困惑。
使用Option Strict On编译此代码以查看问题。 –