如何使用MVVM将DataGridComboBoxColumn绑定到EntityFramework? [英] How do I bind a DataGridComboBoxColumn to EntityFramework using MVVM?

问题描述

我正在尝试使DataGridComboBoxColumn与ViewModel一起使用.一切似乎都能正常工作，但是当我更改组合框的值时，实体没有更改.

I'm trying to get a DataGridComboBoxColumn working with my ViewModel. Everything appears to work correctly but when I change the value of the combo box, the entity isn't changed.

窗口的数据上下文具有以下属性:

The datacontext of the window has these properties:

ItemsSource

Public Property AllEnergySources() As ObservableCollection(Of EnergySourceViewModel)

SelectedItemBinding

  Private _CurrentEnergySource As EnergySourceViewModel
    Public Property CurrentEnergySource() As EnergySourceViewModel
        Get
            Return _CurrentEnergySource
        End Get
        Set(ByVal value As EnergySourceViewModel)
            _CurrentEnergySource = value
            OnPropertyChanged("CurrentEnergySource")
        End Set
    End Property

我觉得问题出在我如何在作为DataContext的ViewModel中填充CurrentEnergySource:

I feel the problem lies with how I populate CurrentEnergySource in the ViewModel that is the DataContext:

Sub New(SelectedEntity as EquipmentEnergySource)
     AllEnergySources = New ObservableCollection(Of EnergySourceViewModel)

    //Select all EnergySources from the EntityFramework
     Dim EnergyEntities = From esr in db.EnergySources Select esr

                //Loop through to convert Entity POCO to Collection of ViewModels
                For Each es In EnergyEntities
                    _AllEnergySources.Add(New EnergySourceViewModel(es))

                    //Optionally Set the newly created ViewModel to SelectedItemBinding object
                    If es.EnergySourceID = SelectedEntity.EnergySourceID Then
                        _CurrentEnergySource = _AllEnergySources.Last
                    End If
                Next
End Sub

当我为组合框创建后备集合时，如果模型是所选模型，则将那个视图模型设置为CurrentEnergySource，但是在那之后它就被断开了(这就是问题所在)

When I create the backing collection for the combobox, if the model is the selected one, I set that viewmodel to be the CurrentEnergySource but after that point it is disconnected(and that's the problem)

我应该在CurrentEnergySource中引用什么，以便在组合框更改时更新模型?

What should I reference in CurrentEnergySource so that it updates the model when the combo box changes?

推荐答案

我的答案是您需要手动更改外键(我现在在CurrentEnergySource的设置器中对其进行更改，这是SelectedItemBinding绑定的属性)

My answer is you need to change the foreign key manually (I now change it in the setter of CurrentEnergySource, which is the SelectedItemBinding bound property)

     Private _CurrentEnergySource As EnergySourceViewModel
    Public Property CurrentEnergySource() As EnergySourceViewModel
        Get
            Return _CurrentEnergySource
        End Get
        Set(ByVal value As EnergySourceViewModel)
            _CurrentEnergySource = value
            Me.Model.EnergySourceID = value.Model.EnergySourceID
            OnPropertyChanged("CurrentEnergySource")
        End Set
    End Property

在加载时，填充私有后备存储_CurrentEnergySource而不是属性，以避免所有对象以修改后的状态开始

On load, populate the private backing store _CurrentEnergySource instead of the property to avoid all objects starting out with modified state

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