Xamarin Forms Switch Toggled事件未与ViewModel绑定

本文介绍了Xamarin Forms Switch Toggled事件未与ViewModel绑定的处理方法，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Forms XAML页面，在其中有一个列表视图，每个元素都有一个Switch(默认为xamarin).我可以将项目中的数据绑定到列表视图，但是我不能订阅Switch事件"Toggled"，因为它会导致项目不显示.我也尝试过使用ICommand和Command，因为它被指示使用按钮，但是结果是相同的，没有显示任何内容.如何处理我的视图模型中的切换开关?

I have a Forms XAML Page and in there I have a listview, and each element has a Switch (xamarin default). I can bind the data from the items to the listview, but I cannot subscrive the Switch event "Toggled", as it causes the item not to show. I also tried with ICommand and Command, as it is instructed to do with buttons, but the result is the same, nothing shown. How can I handle the switch toggle from the my viewmodel?

    <?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="TouristicWallet.Views.WalletManagementPage"
             xmlns:vm="clr-namespace:TouristicWallet.ViewModels"
             xmlns:converters="clr-namespace:TouristicWallet.Converters"
             >

  <ContentPage.BindingContext>
    <vm:WalletManagementViewModel x:Name="ViewModel"/>
  </ContentPage.BindingContext>

  <ContentPage.Resources>
    <ResourceDictionary>
      <converters:CurrencyIdToCodeConverter x:Key="idToCodeConverter"/>
    </ResourceDictionary>
  </ContentPage.Resources>

  <StackLayout>
    <ListView x:Name="MyCurrencies" ItemsSource="{Binding Currencies, Mode=OneWay}">
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <StackLayout Orientation="Horizontal">
              <Label Text="{Binding Currency.Initials, Mode=OneWay}" />
              <Switch IsToggled="{Binding IsOwned, Mode=TwoWay}"
                      Toggled="{Binding Toggled}"
                      />
            </StackLayout>
          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>

  </StackLayout>
</ContentPage>

ViewModel

public class WalletManagementViewModel : ViewModelBase
{

    private readonly List<OwnedCurrencyWrapper> _currencies = new List<OwnedCurrencyWrapper>();
    public List<OwnedCurrencyWrapper> Currencies { get { return _currencies; } }

    public WalletManagementViewModel()
    {
        CurrencyDataAccess cda = new CurrencyDataAccess();
        foreach (var item in cda.GetCurrencies())
        {
            Currencies.Add(new OwnedCurrencyWrapper(item));
        }

        OnPropertyChanged(nameof(Currencies));
    }

    public class OwnedCurrencyWrapper
    {
        public Currency Currency { get; private set; }
        public Boolean IsOwned { get; set; }
        public ICommand Toggled { get; set; }


        public OwnedCurrencyWrapper(Currency currency)
        {
            Currency = currency;
            WalletDataAccess wda = WalletDataAccess.Instance;
            IsOwned = wda.IsOwned(Currency.Id);

            Toggled = new Command(() => Update());
        }

        public void Update()
        {
            WalletDataAccess wda = WalletDataAccess.Instance;
            if (IsOwned) wda.RemoveOwnedCurrency(Currency.Id);
            else wda.OwnCurrency(Currency.Id);

        }

        public void Toggled_handler(object sender, ToggledEventArgs e)
        {
            Update();
        }
    }
}

我没有使用任何mvvm框架

I am not using any mvvm framework

First off a Switch can not bind to a Command. See:https://developer.xamarin.com/guides/xamarin-forms/xaml/xaml-basics/data_bindings_to_mvvm/#Commanding_with_ViewModels

从上面看，可以绑定到ICommand的Forms控件是:

From the above, the Forms controls that can bind to an ICommand are:

按钮
MenuItem
ToolbarItem
SearchBar
TextCell(因此也是ImageCell)
ListView
TapGestureRecognizer

Button
MenuItem
ToolbarItem
SearchBar
TextCell (and hence alsoImageCell )
ListView
TapGestureRecognizer

您只需执行以下操作即可在View的后台代码文件中运行代码，请在XAML中执行此操作:

you can just do the following to run code in the View's code behind file, do this in the XAML:

<Switch IsToggled="{Binding IsOwned, Mode=TwoWay}"
        Toggled="Handle_Toggled" />

然后在文件后面的代码中:

And then in the Code behind file:

void Handle_Toggled(object sender, Xamarin.Forms.ToggledEventArgs e)
{
    // Do stuff
}

或者，由于您是绑定的，因此只需在IsOwned的设置器中添加代码，就可以在实际的OwnedCurrencyWrapper类(这似乎是您想要的)中运行代码.在这种情况下，请不要为开关的Toggled属性分配任何内容:

Alternately, since you are binding, you could run code in the actual OwnedCurrencyWrapper class (which is what you seem to want) just by adding code to the setter for IsOwned. IN this case, don't assign anything to the Toggled property of your switch::

<Switch IsToggled="{Binding IsOwned, Mode=TwoWay}" />

然后在您的OwnedCurrencyWrapper类中:

bool _isOwned;
public bool IsOwned {
    get
    {
        return _isOwned;
    }
    set
    {
        _isOwned = value;
        // Do any other stuff you want here
    }
}

也就是说，由于视图模型未实现INotifyPropertyChanged，因此绑定尚未完成，因此直接对视图模型所做的更改将不会反映在UI中.有关与Forms MVVM绑定的更多信息，请参见: https://developer.xamarin.com/guides/xamarin-表格/xaml/xaml-basics/data_bindings_to_mvvm/

That said, your binding is not complete since your view model is not implementing INotifyPropertyChanged so changes made directly to the view model will not be reflected in the UI. For more info on binding with Forms MVVM, see:https://developer.xamarin.com/guides/xamarin-forms/xaml/xaml-basics/data_bindings_to_mvvm/

更新:我不知道Xamarin表单中的行为.看: https://github.com/xamarin/xamarin-forms-samples /tree/master/Behaviors/EventToCommandBehavior

UPDATE: I was not aware of Behaviors in Xamarin Forms. See:https://github.com/xamarin/xamarin-forms-samples/tree/master/Behaviors/EventToCommandBehavior

因此，这应该允许您将Toggled事件绑定到Command.

So this should allow you to bind the Toggled event to a Command.

这篇关于Xamarin Forms Switch Toggled事件未与ViewModel绑定的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

ICommand