Question

我正在使用自定义控件开发自定义库。当用户在自定义属性中插入无效值时，我需要Visual Studio在设计模式下显示消息，就像Visual Studio在Button中尝试使用Color.Transparent for BorderColor时那样。

一段代码：

Public Class ButtonWithBrigthness 'It inherits from Button in .Designer.vb

  Private _brigthness As Integer

  Public Property Brightness() As Integer
     Get
        Return _brigthness
     End Get
     Set (value as Integer)
        If (value >= 0 And value <= 10) Then
           _brigthness = value
        Else
           'Throw Exception for an invalid value....
        End If
     End Set
  End Property

End Class

Answer 1

要知道您是否处于设计模式，可以使用DesignMode Property。

接下来，您需要知道，如果您在设计模式中从属性设置器中引发异常，属性网格将捕获它并显示一个消息框，说明＆＃34;无效的属性值＆＃34;，用户可以单击on＆＃34;详情＆＃34;查看您输入的自定义消息。如果你想做得更好，你会显示一个消息框，说明它无法正常工作的原因。

无论如何，如果你想提出例外：

Public Property Brightness() As Integer
    Get
       Return _brigthness
    End Get
    Set (value as Integer)
       'I rewrote the condition, but you don't have to, just put the exception in the else...
       If value < 0 Or value > 10 Then
           'Here we throw the Exception only in design mode
           'So at runtime just nothing will happen...
           If Me.DesignMode Then
               Throw New ArgumentOutOfRangeException("Brightness must be between 0 and 10")
           End If
       Else
          _brigthness = value
       End If
    End Set
 End Property

如果你想展示一个漂亮的消息框......

Public Property Brightness() As Integer
    Get
       Return _brigthness
    End Get
    Set (value as Integer)
       If value < 0 Or value > 10 Then
           'Here we show the MessageBox only in design mode
           'So at runtime just nothing will happen...
           If Me.DesignMode Then
               MessageBox.Show("Brightness must be between 0 and 10", "Invalid Brightness Value")
           End If
       Else
          _brigthness = value
       End If
    End Set
 End Property

在自定义属性中抛出消息异常

1 个答案: