将默认值设置为图像 "Public Property"

Question

我尝试将默认值设置为 UserControl 的图像 Public Property。我试图用一个变量来做到这一点，但我得到一个错误 Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.

Private Image_ As Image = My.Resources.MyImage
<Category("Appearance")> <DisplayName("Image")> <DefaultValue(Image_)> <Description("...")>
Public Property Image As Image
    Get
        Return NestedControl.Image
    End Get
    Set(ByVal value As Image)
        NestedControl.Image = value
    End Set
End Property

我也试过像这样设置默认值 <DefaultValue(GetType(Image), "My.Resources.MyImage")> 但是当我重置为 UserControl 的属性时它变成了 "None"!!!

有什么想法吗？

Answer 1

虽然 System.ComponentModel.DefaultValueAttribute 不支持此功能，但您可以使用 old-style ResetPropertyName 和 ShouldSerialize PropertyName方法实现同样的功能。

这在 Defining Default Values with the ShouldSerialize and Reset Methods 中有记载。

Imports System.ComponentModel

Public Class MyUserControl
    Private Image_ As Image = My.Resources.MyImage

    Public Sub New()
        InitializeComponent()
        ResetImage() ' set default
    End Sub

    <Category("Appearance")> <DisplayName("Image")> <Description("...")>
    Public Property Image As Image
        Get
            Return NestedControl.Image
        End Get
        Set(ByVal value As Image)
            NestedControl.Image = value
        End Set
    End Property

    Public Sub ResetImage()
        If Image IsNot Nothing Then Image.Dispose()
        Image = Image_
    End Sub

    Public Function ShouldSerializeImage() As Boolean
        Return (Image IsNot Image_)
    End Function
End Class

将默认值设置为图像 "Public Property"

Set default value to an image "Public Property"

vb.net

user-controls

properties