在Xamarin Forms上创建ICommand Bindable属性

本文介绍了在Xamarin Forms上创建ICommand Bindable属性的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有一个自定义复选框控件，该控件是使用ICommand属性和相应的可绑定属性(我的复选框是Xamarin.Forms XAML页面)创建的，代码是:

I have a custom checkbox control that I created with an ICommand property and the corresponding bindable property (my checkbox is a Xamarin.Forms XAML Page), the code is:

CheckBox.xaml

<Image x:Name="imgCheckBox" WidthRequest="20" HeightRequest="20"/> <Label x:Name="lblCheckBox" TextColor="Black" VerticalOptions="CenterAndExpand"/> <TapGestureRecognizer Tapped="OnCheckBoxTapped"/>

CheckBox.xaml.cs

public partial class CheckBox : ContentView { private static ImageSource uncheckedImage; private static ImageSource checkedImage; public CheckBox() { InitializeComponent(); uncheckedImage = ImageSource.FromResource("cbUnchecked.png"); checkedImage = ImageSource.FromResource("cbChecked.png"); imgCheckBox.Source = uncheckedImage; } public static readonly BindableProperty IsCheckedProperty = BindableProperty.Create<CheckBox, bool>( checkbox => checkbox.IsChecked, false, propertyChanged: (bindable, oldValue, newValue) => { CheckBox checkbox = (CheckBox)bindable; EventHandler<bool> eventHandler = checkbox.CheckedChanged; if (eventHandler != null) { eventHandler(checkbox, newValue); } }); public bool IsChecked { set { SetValue(IsCheckedProperty, value); } get { return (bool)GetValue(IsCheckedProperty); } } void OnCheckBoxTapped(object sender, EventArgs args) { IsChecked = !IsChecked; if (IsChecked) { imgCheckBox.Source = checkedImage; } else { imgCheckBox.Source = uncheckedImage; } } public static readonly BindableProperty CheckBoxCommandProperty = BindableProperty.Create<CheckBox, ICommand>( checkbox => checkbox.CheckBoxCommand, null, BindingMode.TwoWay, propertyChanged: (bindable, oldValue, newValue) => { CheckBox checkbox = (CheckBox)bindable; EventHandler<bool> eventHandler = checkbox.CheckedChanged; if (eventHandler != null) { eventHandler(checkbox, checkbox.IsChecked); } }); public event EventHandler<bool> CheckedChanged; public ICommand CheckBoxCommand { get { return (ICommand)GetValue(CheckBoxCommandProperty); } set { SetValue(CheckBoxCommandProperty, value); } } }

此复选框实现位于另一个名为TermsAndConditionsPage的页面上，该页面也是Xamarin.Forms XAML页面，实现的代码为:

This checkbox implementation is on another Page called TermsAndConditionsPage, that is also a a Xamarin.Forms XAML Page, the code of the implementation is:

<toolkit:CheckBox Text="{Binding txtCheckBox}" FontSize="Small" CheckBoxCommand="{Binding OnCheckBoxTapChanged}" IsChecked="{Binding IsCheckedChanged, Mode=TwoWay}"/> <Button Text="Next" Command="{Binding Next_OnClick}" IsEnabled="{Binding Next_IsEnabled}" HorizontalOptions="CenterAndExpand" Clicked="OnNextClicked"/>

此页面后面的代码为空(使用InitializeComponent()构造). 我也有此页面的ViewModel，其中包含以下代码:

The Code Behind of this page is empty (Constructur with InitializeComponent()). I also have the ViewModel of this page with this code:

TermsAndConditionsViewModel.cs

private string _txtCheckBox; public string txtCheckBox { get { return _txtCheckBox; } set { _txtCheckBox = value; OnPropertyChanged("txtCheckBox"); } } private bool _Next_IsEnabled; public bool Next_IsEnabled { get { return _Next_IsEnabled; } set { _Next_IsEnabled = value; OnPropertyChanged("Next_IsEnabled"); } } private bool _IsCheckedChanged; public bool IsCheckedChanged { get { return _IsCheckedChanged; } set { _IsCheckedChanged = value; OnPropertyChanged("IsCheckedChanged"); } } public ICommand Next_OnClick { get; set; } public ICommand OnCheckBoxTapChanged { get; set; } public TermsAndConditionsViewModel() { txtCheckBox = "I agree with the terms and conditions"; Next_OnClick = new Command(NextClicked); OnCheckBoxTapChanged = new Command(CheckBoxTapped); } private void CheckBoxTapped() { if (IsCheckedChanged) { Next_IsEnabled = true; } else { Next_IsEnabled = false; } } private void NextClicked() { App.Current.MainPage = new Views.HelloWorld(); } #region INPC public void OnPropertyChanged(string propertyName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } public event PropertyChangedEventHandler PropertyChanged; #endregion

现在，提问时间:我遇到的问题是CheckBoxTapped Command不起作用，我的意思是，它什么也没有做，尽管每次我触摸复选框图像都会更改，但它不会更改Next_IsEnabled我的按钮的属性.我想知道我在这里缺少什么来使此命令正常工作.

Now, the question time: the problem I'm having is the CheckBoxTapped Command is not working, I mean, it doesn't do anything, although the checkbox image changes every time I touch it, it does not change the Next_IsEnabled property of my button. I'd like to know what I am missing here to make this command work properly.

编辑

我要寻找的是一个与Button具有相似行为的命令.

What I'm looking for is a Command that behaves similarly to the one that Buttons have.

感谢您的光临！

推荐答案

由于原始答案现在已过时，因此这是新方法:

Since the original answer is now obsolete, here is the new method:

using System.Windows.Input; public partial class MyControlExample : ContentView { // BindableProperty implementation public static readonly BindableProperty CommandProperty = BindableProperty.Create(nameof(Command), typeof(ICommand), typeof(MyControlExample), null); public ICommand Command { get { return (ICommand)GetValue(CommandProperty); } set { SetValue(CommandProperty, value); } } // Helper method for invoking commands safely public static void Execute(ICommand command) { if (command == null) return; if (command.CanExecute(null)) { command.Execute(null); } } public MyControlExample() { InitializeComponent(); } // this is the command that gets bound by the control in the view // (ie. a Button, TapRecognizer, or MR.Gestures) public Command OnTap => new Command(() => Execute(Command)); }