使用IDataErrorInfo禁用按钮

Question

我找到了本教程，并且能够实现它。

当发生错误时，如何禁用按钮？

我在网上搜索了很多，但找不到一段类似我的代码。(是的，我知道关于这件事有无数条线索，但我就是不明白。)

下面是我当前的代码，它有点长：

Public Class GradeVm
    Implements IDataErrorInfo

    Public Interface IDataErrorInfo
        Default ReadOnly Property Item(columnName As String) As String
        ReadOnly Property [Error]() As String
    End Interface

    #Region "Properties"
    Property Grade As Integer
    Property Adjust As Integer
    #End Region

    Public ReadOnly Property [Error] As String Implements IDataErrorInfo.Error
        Get
            Return "Error"
        End Get
    End Property

    Default Public ReadOnly Property Item(columnName As String) As String Implements IDataErrorInfo.Item
        Get
            Select Case columnName
                Case "Grade"
                    If IsNumeric(Me.Grade) = False Then
                        Return [Error]
                    End If
                Case "Adjust"
                    If IsNumeric(Me.Adjust) = False Then
                        Return [Error]
                    End If
            End Select

            Return ""
        End Get
    End Property
    End Class

Answer 1

这和这里的代码结合在一起完成了这个任务！最后:)

Answer 2

如果要将按钮绑定到RelayCommand，可以通过设置CanExecute()函数返回False来禁用该按钮：

Public Function CanExecute(parameter As Object) As Boolean Implements ICommand.CanExecute
    Return False
End Function

但RelayCommand并不意味着要以这种方式使用。我建议选择一个MVVM框架(例如MVVMLight)，这样您就可以获得更好的RelayCommand实现。然后你可以像这样使用它：

Private _myCommand As RelayCommand = New RelayCommand(Me.ExecuteCommand, Me.CanExecuteCommand)
Public ReadOnly Property MyCommand As ICommand
    Get
        Return Me._myCommand
    End Get
End Property

Private Sub ExecuteCommand()
    ......
End Sub

Private Function CanExecuteCommand() As Boolean
    'do logic to disable (return false) or enable (return true) button
    'based on specific criteria
    'just for example, disable the button forever :
    Return False
End Function

更新:

为什么要删除RelayCommand实现？第一种方法是在最初的文章中使用RelayCommand，但是将CanExecute()函数的返回值改为False而不是True。然后，您可以在ViewModel中使用它，如下所示：

Private _myCommand As RelayCommand = New RelayCommand()
Public ReadOnly Property MyCommand As ICommand
    Get
        Return Me._myCommand
    End Get
End Property