Question

我的usercontrol上有一个按钮

<Button Grid.Row="13" Grid.Column="7" Content="Save" Name="btnSave" 
            CommandParameter="{Binding CompanyDetails}"
            Command="{Binding SaveCommand}" />

SaveCommand是在ViewModel中声明的RelayCommand。 CompanyDetails是同一ViewModel中的属性。上面提到的ViewModel是我的UserControl的datacontext。

    Public Class CompanyViewModel
    Inherits ViewModelBase
    Implements IDataErrorInfo

    Private _myData As DataFromDatabase      
    Private _companyDetails As New CompanyDetailsBase
    Private _saveCommand As RelayCommandWithParameter

    Public Property CompanyDetails() As CompanyDetailsBase
        Get
            Return _companyDetails
        End Get
        Set(ByVal value As CompanyDetailsBase)
            _companyDetails = value
            OnPropertyChanged("CompanyDetails")
        End Set
    End Property

    Public Property SaveCommand() As RelayCommandWithParameter
        Get
            If _saveCommand Is Nothing Then
                Dim saveAction As New Action(Of Object)(AddressOf Me.SaveIt)
                _saveCommand = New RelayCommandWithParameter(saveAction) ', Me.CanSave)
            End If
            Return _saveCommand
        End Get

        Set(ByVal value As RelayCommandWithParameter)
            _saveCommand = value
        End Set
    End Property

    Public Sub New()
        _myData = New DataFromDatabase(My.Settings.ConnectionString)
        _saveCommand = New RelayCommandWithParameter(New Action(Of Object)(AddressOf SaveIt))
    End Sub

    Public Function GetCompanyDetails(ByVal sap As String) As CompanyDetailsBase
        CompanyDetails = _myData.GetCompanyDetails(sap)
        Return CompanyDetails
    End Function

    Public Sub SaveIt(ByVal c As CompanyDetailsBase)
        MessageBox.Show("Save customer " & c.Sap)
    End Sub

    End Class

usercontrol上的其他字段绑定到ObjectDataProvider，后者调用GetCompanyDetails函数。每次调用此函数时，CompanyDetails都会被设置，直到我调用SaveIt子例程。调用SaveIt时，其参数始终为Nothing。我在哪里弄错了？非常感谢你的回答。

Answer 1

在 CompanyViewModel 的构造中，使用 GetCompanyDetails 函数填充 CompanyDetails 。将构造函数更改为以下，

Public Sub New()
    _myData = New DataFromDatabase(My.Settings.ConnectionString)
    _saveCommand = New RelayCommandWithParameter(New Action(Of Object)(AddressOf SaveIt))
    _companyDetails = GetCompanyDetails()  
End Sub

这可能会有所帮助。祝你好运。

Answer 2

自从我做VB以来已经有一段时间了，我从来没有用WPF做过，但我想我知道你的问题是什么。

初始化Command的方式，实际上并没有传递参数。

当我在c＃中执行此操作时，它看起来像=＆gt;

_saveCommand = new RelayCommandWithParameter(
            (param) =>
            {
                SaveIt((int)param);
            },
               // this line is the same as your commented out Me.CanSave
            (param) => { return this.CanDisplaySelectedPolicy; });

所以你可以看到在lamda表达式中我传递了一个名为param的参数，然后将其放入SaveIt方法中。

当您创建新动作时，请尝试在其中放置一个lamda表达式，如上所示，因此您可以将参数传递给SaveIt方法。

RelayCommand commandParameter为null

2 个答案: