wpf - 在 F# WPF MVVM 应用程序中绑定(bind)到 TextBox 的 TextChanged 事件

Question

我想绑定(bind)到使用 FsXaml 和 FSharp.ViewModule 构建的 MVVM F# 应用程序中的 WPF TextBox。我向描述的应用程序添加了一个名为“SetA”的命令 here ，并尝试使用以下 XAML 绑定(bind)到它:

<TextBox Text="{Binding Score.ScoreA, Mode=OneWay}" FontFamily="Lucida Console">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="TextChanged">
            <fsx:EventToCommand Command="{Binding SetA}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</TextBox>

TextBox 是从 ScoreA 属性正确填充的，但是当我在 TextBox 中键入新值时，不会调用 SetA 命令。我对 F# 很满意，但这是我的第一个 WPF MVVM 应用程序，所以我不确定我做错了什么。当用户更改文本值时，如何触发我的 SetA 处理程序？

这是我的 View 模型:

type MainViewModel(controller : Score -> ScoringEvent -> Score) as self = 
    inherit EventViewModelBase<ScoringEvent>()

    let score = self.Factory.Backing(<@ self.Score @>, Score.zero)

    let eventHandler ev =
        score.Value <- controller score.Value ev

    do
        self.EventStream
        |> Observable.add eventHandler

    member this.IncA = this.Factory.EventValueCommand(IncA)
    member this.DecA = this.Factory.EventValueCommandChecked(DecA, (fun _ -> this.Score.ScoreA > 0), [ <@@ this.Score @@> ])
    member this.IncB = this.Factory.EventValueCommand(IncB)
    member this.DecB = this.Factory.EventValueCommandChecked(DecB, (fun _ -> this.Score.ScoreB > 0), [ <@@ this.Score @@> ])
    member this.NewGame = this.Factory.EventValueCommand(New)
    member this.SetA = this.Factory.EventValueCommand(SetA)

    member __.Score = score.Value 

我只添加了定义 SetA 的一行。

Answer 1

很可能正在调用 Command，但结果不是您所期望的。

出于测试目的尝试

member this.SetA = 
   this.Factory.CommandSync(
        fun _ -> System.Windows.MessageBox.Show("TextChanged","RoutedEv") |> ignore)

请注意 CommandSync 而不是 EventValueCommand。无论您如何更改分数，都会弹出一个消息框。

您还可以保留 EventValueCommand

member this.SetA = this.Factory.EventValueCommand(SetA)

并在 update 中做同样的事情

let update score event =
    match event with
    | IncA -> {score with ScoreA = score.ScoreA + 1}
    | DecA -> {score with ScoreA = max (score.ScoreA - 1) 0}
    | IncB -> {score with ScoreB = score.ScoreB + 1}
    | DecB -> {score with ScoreB = max (score.ScoreB - 1) 0}
    | New -> zero 
    | SetA -> System.Windows.MessageBox.Show("TextChanged","RoutedEv") |> ignore ; score

回到不是您所期望的 部分，我假设您希望记分牌中的分数在您更改 TextBox.Text 值时更新。

正如您所注意到的，没有(纯粹的)方法可以使用当前的 controller 将 TextBox.Text 值带入 update 中. 由于 SetX 行为未修复，这与 IncX、DecX 或 New 事件不同。

选项:

• 您可以将 Controller 的签名更改为 Score -> ScoringEvent -> string option -> Score 并使用选项值来处理 update 有趣。

• 您可以处理 ViewModel 中的所有内容。 记录的不可变特性强制使用 OneWay Binding。我会保持它不可变，但您可以(分解)组合 ViewModel 中的所有内容。

尝试

View 模型

type MainViewModel(controller : Score -> ScoringEvent -> Score) as self = 
    inherit EventViewModelBase<ScoringEvent>()

    let scoreA = self.Factory.Backing(<@ self.ScoreA @>, 0)
    let scoreB = self.Factory.Backing(<@ self.ScoreB @>, 0)

    let updateVM score = 
        scoreA.Value <- score.ScoreA
        scoreB.Value <- score.ScoreB

    let eventHandler ev = 
        updateVM <| controller {ScoreA = scoreA.Value ; ScoreB = scoreB.Value} ev

    do
        self.EventStream
        |> Observable.add eventHandler

    member this.IncA = this.Factory.EventValueCommand(IncA)
    member this.DecA = this.Factory.EventValueCommandChecked(DecA, (fun _ -> this.ScoreA > 0), [ <@@ this.ScoreA @@> ])
    member this.IncB = this.Factory.EventValueCommand(IncB)
    member this.DecB = this.Factory.EventValueCommandChecked(DecB, (fun _ -> this.ScoreB > 0), [ <@@ this.ScoreB @@> ])
    member this.NewGame = this.Factory.EventValueCommand(New)

    member __.ScoreA
        with get() = scoreA.Value 
         and set v = scoreA.Value <- v
    member __.ScoreB
        with get() = scoreB.Value 
         and set v = scoreB.Value <- v

XAML

<DockPanel LastChildFill="True">
    <StackPanel DockPanel.Dock="Bottom" Height="75" Orientation="Horizontal" Background="#FF3A3A3A">
        <Button Height="70" Width="70" Margin="2" Command="{Binding NewGame}">
            <TextBlock Text="New" FontSize="18"></TextBlock>
        </Button>
        <TextBox Text="{Binding ScoreA, UpdateSourceTrigger=PropertyChanged}" 
                 Margin="2" FontSize="18" HorizontalContentAlignment="Center" VerticalContentAlignment="Center">
        </TextBox>
    </StackPanel>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <Border Background="#FF024D70" Grid.Column="0">
            <Grid>
                <Viewbox>
                    <Label Content="{Binding ScoreA}" ContentStringFormat="D2" FontFamily="Lucida Console"></Label>
                </Viewbox>
                <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
                    <Button Command="{Binding DecA}"  Height="70" Width="70" VerticalAlignment="Bottom" Opacity="0.5" Margin="20">
                        <TextBlock Text="-" FontSize="36" Height="60"></TextBlock>
                    </Button>
                    <Button Command="{Binding IncA}"  Height="70" Width="70" VerticalAlignment="Bottom" Opacity="0.5" Margin="20">
                        <TextBlock Text="+" FontSize="36" Height="60"></TextBlock>
                    </Button>
                </StackPanel>
            </Grid>
        </Border>
        <Border Background="#FF7E0E03" Grid.Column="1">
            <Grid>
                <Viewbox>
                    <Label Content="{Binding ScoreB}" ContentStringFormat="D2"  FontFamily="Lucida Console"></Label>
                </Viewbox>
                <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
                    <Button Command="{Binding DecB}"  Height="70" Width="70" VerticalAlignment="Bottom" Opacity="0.5" Margin="20">
                        <TextBlock Text="-" FontSize="36" Height="60"></TextBlock>
                    </Button>
                    <Button Command="{Binding IncB}"  Height="70" Width="70" VerticalAlignment="Bottom" Opacity="0.5" Margin="20">
                        <TextBlock Text="+" FontSize="36" Height="60"></TextBlock>
                    </Button>
                </StackPanel>
            </Grid>
        </Border>
    </Grid>
</DockPanel>

注释

• Score.ScoreX 更改为 ScoreX
• Text="{Binding Score.ScoreA, Mode=OneWay}" 更改为 Text="{Binding ScoreA, UpdateSourceTrigger=PropertyChanged}"
• 删除了 Interaction.Trigger