在我的之前的问题中,我问了如何使用WPF和MVVM来制作一个可关闭的对话框,用于在F#中添加新的Person记录。现在我的下一步是制作另一个对话框来编辑这些记录。但我还没有想出如何将现有记录传递给ViewModel,并用它来填充对话框的字段。我得到异常,因为F#记录是不可变的,而ViewModel似乎希望得到一个可变对象。
我将展示现有添加对话框的代码 - 假设编辑对话框看起来相同。
这是Person记录:
以下是添加对话框的XAML代码:
这是它(简化版)的视图模型:
那么我如何使用这种方法(或类似的方法)来打开一个相同的编辑对话框,并使用所选人员来填充其字段呢?
我将展示现有添加对话框的代码 - 假设编辑对话框看起来相同。
这是Person记录:
type Person = { Name: string; Email: string }
以下是添加对话框的XAML代码:
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:fsxaml="http://github.com/fsprojects/FsXaml"
xmlns:local="clr-namespace:ViewModels;assembly=Test3"
local:DialogCloser.DialogResult="{Binding DialogResult}"
Title="Add Person" Height="150" Width="210" ResizeMode="NoResize" >
<Window.DataContext>
<local:PersonAddVM />
</Window.DataContext>
<StackPanel>
<Grid FocusManager.FocusedElement="{Binding ElementName=_name}">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="50" />
<ColumnDefinition Width="140" />
</Grid.ColumnDefinitions>
<Label Content="_Name" Target="_name" Grid.Row="0" Grid.Column="0" Margin="2" />
<TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" x:Name="_name"
Grid.Row="0" Grid.Column="1" Margin="4" />
<Label Content="_Email" Target="_email" Grid.Row="2" Grid.Column="0" Margin="2" HorizontalAlignment="Left" />
<TextBox Text="{Binding Email, UpdateSourceTrigger=PropertyChanged}" x:Name="_email"
Grid.Row="1" Grid.Column="1" Margin="4" />
</Grid>
<UniformGrid Rows="1" Columns="2" VerticalAlignment="Center" Margin="2,20,2,2" >
<Button Content="OK" IsDefault="True" IsEnabled="{Binding IsValid}" Command="{Binding OkCmd}"
HorizontalAlignment="Right" Margin="6,0" Width="50" />
<Button Content="Cancel" IsCancel="True" HorizontalAlignment="Left" Margin="6,0" Width="50" />
</UniformGrid>
</StackPanel>
</Window>
这是它(简化版)的视图模型:
type PersonAddVM() as self =
inherit DialogVMBase() // ViewModelBase with a DialogResult property
let name = self.Factory.Backing( <@ self.Name @>, "", hasLengthAtLeast 4 )
let email = self.Factory.Backing( <@ self.Email @>, "", hasLengthAtLeast 5 )
let makePerson () = { Name = name.Value; Email = email.Value }
member self.Name with get() = name.Value and set value = name.Value <- value
member self.Email with get() = email.Value and set value = email.Value <- value
member self.OkCmd = self.Factory.CommandSync( fun () ->
PersonCache.Add (makePerson()) // PersonCache is based on an Observable Dictionary
self.DialogResult <- true )
并且添加对话框是从一个列表所有人的PersonList对话框中打开的,该对话框具有以下ViewModel代码:
type PersonListView = XAML<"PersonListView.xaml">
type PersonAddView = XAML<"PersonAddView.xaml">
module PersonViewHandling =
let OpenList() = DialogHelper.OpenDialog (PersonListView())
let OpenAdd() = DialogHelper.OpenDialog (PersonAddView()) // Calls ShowDialog on the view and handles the result
type PersonListVM() as self =
inherit DialogVMBase()
// I want to use the next 3 lines to access the Person selected in the list,
// to pass it to the Edit dialog
let emptyPerson = { Name = ""; Email = "" }
let selectedPerson = self.Factory.Backing( <@ self.SelectedPerson @>, emptyPerson )
member self.SelectedPerson with get() = selectedPerson.Value and set value = selectedPerson.Value <- value
member self.AddCmd = self.Factory.CommandSync (fun _ -> PersonViewHandling.OpenAdd() |> ignore)
那么我如何使用这种方法(或类似的方法)来打开一个相同的编辑对话框,并使用所选人员来填充其字段呢?
PersonAddVM
类:创建一个具有可变字段的类,并将其交给 WPF 适当地进行修改。然后,一旦你知道 WPF 修改你的类完成并且其字段包含最终值(例如,当用户在对话框上单击“确定”时),你可以使用makePerson
等函数从这些字段的当前值创建 F# 记录,并在其余代码中使用该不可变记录。 - rmunn