在MVVM中，可以在视图的代码后面访问ViewModel吗？ [英] In MVVM is it acceptable to access the ViewModel in the view's code behind?

问题描述

在MVVM模式中，是否可以接受甚至可以在后面的视图代码中访问ViewModel属性？

IN an MVVM pattern is it acceptable or even possible to access ViewModel properties in the views code behind?

我有一个可观察的集合，该集合可填充到ViewModel中。我需要在视图中使用它来绑定到带有链接列表的无尽报价器。即

I have an observable collection which is populated in the ViewModel. I need to use it in the view to bind to an endless ticker with a linked list. i.e.

    private LinkedList<Border> tickerForex = new LinkedList<Border>();

    public ForexBuy()
    {
        InitializeComponent();
        DataContext = new ForexViewModel();
    }

    private void InitializeForexTicker()
    {
        CanvasForexBuyTicker.Children.Clear();
        foreach (var currency in DataContext.Currencies) //Is this possible/allowable???
        {
           AddTickerItem(currency);
        }

        CanvasForexBuyTicker.Dispatcher.BeginInvoke(DispatcherPriority.Background, new DispatcherOperationCallback(delegate
        { var node = tickerForex.First;

            while (node != null)
            {
                if (node.Previous != null)
                {
                    Canvas.SetLeft(node.Value, Canvas.GetLeft(node.Previous.Value) + node.Previous.Value.ActualWidth + gap);
                }
                else
                {
                    Canvas.SetLeft(node.Value, CanvasForexBuyTicker.Width + gap);
                }

                node = node.Next;
            }

            return null;

        }), null);

}

void AddTickerItem(Currency currency)
    {
        Border border = new Border();
        border.Background = new SolidColorBrush(Color.FromArgb(255, 0, 99, 99));

        if (currency.IsUpward == 0)
        {
            border.Background = new SolidColorBrush(Color.FromArgb(255, 255, 153, 0));
        }

        border.BorderThickness = new Thickness(3);
        border.BorderBrush = new SolidColorBrush(Colors.White);
        border.CornerRadius = new CornerRadius(10);
        border.Width = Double.NaN;
        border.Height = 35;

        UIHelper.CanvasAutoSize canvas = new UIHelper.CanvasAutoSize();
        canvas.Background = Brushes.Green;  
        canvas.Tag = currency;
        canvas.Height = Double.NaN;

        TextBlock tb = new TextBlock
        {
            Text = currency.Code + " " + currency.Sell + " ",
            FontSize = 22,
            FontWeight = FontWeights.Bold,
            Foreground = Brushes.Black
        };

        tb.SetValue(Canvas.LeftProperty, 8d);
        tb.SetValue(Canvas.TopProperty, 2d);
        canvas.Children.Add(tb);

        tb.TouchDown += TouchTickerItem;

        border.Child = canvas;

        CanvasForexBuyTicker.Children.Add(border);
        Canvas.SetTop(CanvasForexBuyTicker, 3);
        Canvas.SetLeft(CanvasForexBuyTicker, 0);

        tickerForex.AddLast(border);
    }

关于调度员是否应从ViewModel触发，我有些困惑或是否在后面的视图代码中使用它。

I'm a little lost as to whether the dispatcher should fire from the ViewModel or whether to use it in the views code behind.

推荐答案

如果问题只是关于如何从后面的代码访问ViewModel的问题，则只需将DataContext强制转换为适当的类型：

If the question is just about how to access the ViewModel from code behind, you could simply cast the DataContext to the proper type:

var viewModel = (MyViewModel)DataContext;

foreach (var currency in viewModel.Currencies)
{
    ...
}

是否可以接受这取决于口味。通过视图XAML中的绑定或背后的一段代码访问视图模型，我看不出任何根本区别。

If this is acceptable or not is a matter of taste. I do not see any fundamental difference in accessing the view model by bindings in the view's XAML or by a piece of code-behind.

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