如何在viewmodel上使用DelegateCommand?

时间:2016-01-09 12:22:44

标签: f#

是否有关于如何在用F#编写的viewmodel上调用DelegateCommand的示例?

我找到了以下CodeateCommand实现here的代码:

type DelegateCommand<a>(execute : 'a -> unit, ?canExecute : 'a  ->  bool) =
  let event = Event<_,_>()
  interface ICommand with
    member this.CanExecute(param : obj) =
      if canExecute.IsSome then
        canExecute.Value(param :> 'a)
      else true
    member this.Execute (param : obj) =
      execute(param :> 'a)

然而,作为F#的新手,我不确定是否应该使用此实现,或者我是否应该利用其他方法。

这是我想知道如何执行DelegateCommand后我想执行的测试:

module CreateProfileViewModel.Tests

open FsUnit
open NUnit.Framework
open CreateProfile.UILogic

[<Test>]
let ``create profile`` () =

    // Setup
    let viewModel = ViewModel()
    viewModel.FirstName <- "Scott"
    viewModel.LastName <- "Nimrod"

    // Test
    viewModel.Submit.Execute();

    // Verify
    let expected = false // TODO - implement some state-change
    expected |> should equal true

我的viewmodel如下:

module CreateProfile

open Core.UILogic

type ViewModel() =
    inherit ViewModelBase()
    let mutable firstName = ""
    let mutable lastName = ""

    member this.FirstName
        with get() = firstName 
        and set(value) =
            firstName <- value
            base.NotifyPropertyChanged(<@ this.FirstName @>)

    member this.LastName
        with get() = lastName 
        and set(value) =
            lastName <- value
            base.NotifyPropertyChanged(<@ this.LastName @>)

我有以下基本视图模型:

module Core.UILogic

open System.ComponentModel
open Microsoft.FSharp.Quotations.Patterns

type ViewModelBase () =
    let propertyChanged = 
        Event<PropertyChangedEventHandler,PropertyChangedEventArgs>()

    let getPropertyName = function 
        | PropertyGet(_,pi,_) -> pi.Name
        | _ -> invalidOp "Expecting property getter expression"

    interface INotifyPropertyChanged with
        [<CLIEvent>]
        member this.PropertyChanged = propertyChanged.Publish

    member private this.NotifyPropertyChanged propertyName = 
        propertyChanged.Trigger(this,PropertyChangedEventArgs(propertyName))

    member this.NotifyPropertyChanged quotation = 
        quotation |> getPropertyName |> this.NotifyPropertyChanged

更新

我已将F#的MVVM项目模板中定义的RelayCommand修改为以下内容:

module UILogic.Interaction

open System
open System.Windows
open System.Windows.Input
open System.ComponentModel

type DelegateCommand (action:(obj -> unit), canExecute:(obj -> bool)) =
    let event = new DelegateEvent<EventHandler>()
    interface ICommand with
        [<CLIEvent>]
        member this.CanExecuteChanged = event.Publish
        member this.CanExecute arg = canExecute(arg)
        member this.Execute arg = action(arg)

然后我更新了我的viewmodel,如下所示:

module CreateProfile.UILogic

open UILogic.State
open UILogic.Interaction

type ViewModel() =
    inherit ViewModelBase()

    let mutable _firstName = ""
    let mutable _lastName = ""
    let mutable _submitted = false

    member this.FirstName
        with get() = _firstName 
        and set(value) =
            _firstName <- value
            base.NotifyPropertyChanged(<@ this.FirstName @>)

    member this.LastName
        with get() = _lastName 
        and set(value) =
            _lastName <- value
            base.NotifyPropertyChanged(<@ this.LastName @>)

    member this.IsSubmitted
        with get() = _submitted
        and set(value) = _submitted <- value

    member this.Submit =
        new DelegateCommand ((fun _ -> this.IsSubmitted <- true), (fun _ -> true))

但是,我不知道如何在Submit (DelegateCommand)上调用Execute函数:

module CreateProfileViewModel.Tests

open FsUnit
open NUnit.Framework
open UILogic.State
open CreateProfile.UILogic

[<Test>]
let ``create profile`` () =

    // Setup
    let viewModel = ViewModel()
    viewModel.FirstName <- "Scott"
    viewModel.LastName <- "Nimrod"

    // Test
    ignore viewModel.Submit.Execute(); // How to invoke execute?

    // Verify
    viewModel.IsSubmitted |> should equal true

我知道这是微不足道的,但老实说,我不知道如何做到这一点。

有什么建议吗?

2 个答案:

答案 0 :(得分:3)

Submit实施更改为:

member this.Submit =
    DelegateCommand ((fun _ -> this.IsSubmitted <- true), (fun _ -> true)) :> ICommand

并将其称为:

viewModel.Submit.Execute() |> ignore

重要的变化是Submit方法的返回类型现在是ICommand而不是DelegateCommand。这是由于使用了向上运算符:>

在F#中,所有界面都明确实施。这意味着虽然DelegateCommand实现了ICommand,但ICommand的方法在声明(或推断)为DelegateCommand的对象上不可见。当声明(或推断)值为ICommand类型时,另一方面,只有ICommand的成员可用。

答案 1 :(得分:2)

由于我没有在F#中使用MVC或MVVM,因此无法给出具体的代码示例。

有关

  

然而,作为F#的新手,我不确定是否应该使用它   实施或是否有其他方法我应该   杠杆。

如果您使用的Visual Studio也可以免费下载community edition,那么MVC和MVVM都有模板。

使用菜单从VS访问模板。

档案 - &gt;新 - &gt;项目

enter image description here

在线扩展
展开模板
展开Visual F#

enter image description here

在&#34;搜索在线模板的右上方&#34;输入一个术语,如MVC或MVVM

enter image description here

选择一个或检查几个。

注意:有些模板已经存在了几年,而且F#和Windows在此过程中取得了很大进展,因此我倾向于避免使用较旧的模板。此外,流行的作者通常可以在网上找到,甚至有些人都在这里,所以请询问有关细节的问题。

您还可以使用互联网浏览器在Visual Studio Gallery查看VS的其他模板,控件和扩展程序

警告:某些扩展程序会在安装时出现问题,尤其是较旧或较不受欢迎的扩展程序,因此请小心并且不要将它们安装在生产计算机上,直到您对其进行测试为止先是另一台机器。