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目标

我希望在btnRefresh文本框中有内容时启用按钮tbMachineNo（使用 MVVM 标准）。

项目总结

我有一个：

窗口.xaml

<TextBox Text="{Binding Inspection.Machine.MachineNumber, UpdateSourceTrigger=PropertyChanged}" />
<Button Command="{Binding RefreshMachineNo}" />

检查视图模型.vb

这有一个属性InspectionModel并包含几个方法。一个是我的 ICommand 在我的构造函数期间被执行（这就是由于该CanUpdate方法而禁用/启用我的文本框的原因）

Public Class InspectionViewModel
    Private _Inspection As InspectionModel
    Private _RefreshMachineNo As ICommand

    Public Property Inspection As InspectionModel
        Get
            Return _Inspection
        End Get
        Set(value As InspectionModel)
            _Inspection = value
        End Set
    End Property

    Public Sub New()
        _Inspection = New InspectionModel("Version", "Title of machine", "Model", "Owner", "Department", Date.Now, New MachineModel)
        RefreshMachineNo = New RefreshMachineNumberCommand(Me) 'Calls the CanUpdate, and if it returns true, it executes FetchMachineDetails()
    End Sub

    Public Property RefreshMachineNo As ICommand
        Get
            Return _RefreshMachineNo
        End Get
        Set(value As ICommand)
            _RefreshMachineNo = value
        End Set
    End Property

    Public ReadOnly Property CanUpdate As Boolean
        Get
            If Inspection Is Nothing Then
                Return False
            End If
           Return Not String.IsNullOrWhiteSpace(Inspection.Machine.MachineNumber)
        End Get
    End Property

    Public Sub FetchMachineDetails()
        Dim MachineNo As String = Inspection.Machine.MachineNumber
    End Sub
End Class

这工作正常，代码在它应该执行的时候执行。现在看看我的 InpsectionModel。

RefreshMachineNumber 命令

Public Class RefreshMachineNumberCommand
    Implements ICommand

    Private _viewModel As InspectionViewModel

    Public Sub New(ByVal viewModel As InspectionViewModel)
        _viewModel = viewModel
    End Sub

    Public Event CanExecuteChanged(sender As Object, e As System.EventArgs) Implements System.Windows.Input.ICommand.CanExecuteChanged

    Public Function CanExecute(parameter As Object) As Boolean Implements System.Windows.Input.ICommand.CanExecute
        Return _viewModel.CanUpdate()
    End Function

    Public Sub Execute(parameter As Object) Implements System.Windows.Input.ICommand.Execute
        _viewModel.FetchMachineDetails()
   End Sub
End Class

检查模型.vb

这个类继承了我的 ObservableObject ，它实现了INotifyPropertyChanged. 所以理论上，每当我MachineNumber的检查对象中的属性发生变化时Machine，它都应该触发UpdateSourceTrigger=PropertyChanged

Public Class InspectionModel
    Inherits ObservableObject

    Private _Version As String
    Private _Title As String
    Private _Model As String
    Private _InspectionOwner As String
    Private _Department As String
    Private _DateEntry As Date
    Private _Machine As MachineModel

    Public Property Version As String
        Get
            Return _Version
        End Get
        Set(value As String)
            _Version = value
            Notify("Version")
        End Set
    End Property
    Public Property Title As String
        Get
            Return _Title
        End Get
        Set(value As String)
            _Title = value
            Notify("Title")
        End Set
    End Property
    Public Property Model As String
        Get
            Return _Model
        End Get
        Set(value As String)
            _Model = value
            Notify("Model")
        End Set
    End Property
    Public Property InspectionOwner As String
        Get
            Return _InspectionOwner
        End Get
        Set(value As String)
            _InspectionOwner = value
            Notify("InspectionOwner")
        End Set
    End Property
    Public Property Department As String
        Get
            Return _Department
        End Get
        Set(value As String)
            _Department = value
            Notify("Department")
        End Set
    End Property
    Public Property DateEntry As Date
        Get
            Return _DateEntry
        End Get
        Set(value As Date)
            _DateEntry = value
            Notify("DateEntry")
        End Set
    End Property
    Public Property Machine As MachineModel
        Get
            Return _Machine
        End Get
        Set(value As MachineModel)
            _Machine = value
            Notify("Machine")
        End Set
    End Property

    Public Sub New(ByVal Version As String, ByVal Title As String, ByVal Model As String, ByVal InspectionOwner As String, ByVal Department As String, ByVal DateEntry As Date, ByVal Machine As MachineModel)
        Me.Version = Version
        Me.Title = Title
        Me.Model = Model
        Me.InspectionOwner = InspectionOwner
        Me.Department = Department
        Me.DateEntry = DateEntry
        Me.Machine = Machine
    End Sub
End Class

问题

当文本框填充字符或为空时，我没有掌握如何启用/禁用我的按钮控件。我的CanUpdateICommand 是当前控制它的，并且仅在加载构造函数时执行一次。

这是有道理的，但我不确定如何在不放置代码的情况下使这个 Textchanged 问题正常工作。我希望能够使用 MVVM 来做到这一点

我将我的文本框绑定到另一个字段，并且该字段绑定到 Inspection 对象中的相同属性。当我在文本框中输入时，我可以看到另一个字段被修改......所以 UpdateSourceTrigger 正在工作，但是当我输入文本时我无法启用按钮。

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2 回答 2

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  1. 确保您的 UpdateSourceTrigger 设置为 PropertyChanged
  2. 在您的属性设置器中，调用RefreshMachineNo.RaiseCanExecuteChanged()

RaiseCanExecuteChanged 是在 DelegateCommand 和 RelayCommand 上找到的标准方法。希望您正在为您的命令使用行业标准的 ICommand 实现之一。

于 2013-11-05T16:25:31.893 回答
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我的问题出现在我的RefreshMachineNumberCommand.vb课堂上。

更具体地说，我的 CanExecuteChanged 事件没有处理 CommandManager。这是我为修复它所做的：

Public Custom Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged
    AddHandler(ByVal value As EventHandler)
        AddHandler CommandManager.RequerySuggested, value
    End AddHandler

    RemoveHandler(ByVal value As EventHandler)
        RemoveHandler CommandManager.RequerySuggested, value
    End RemoveHandler

    RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
        CanExecute(sender)
    End RaiseEvent
End Event

有关更多信息，这篇文章对我帮助很大！

于 2013-11-05T16:29:33.423 回答