KnockOutJS – Multiple ViewModels in a single View

data-bindingknockout-mapping-pluginknockout.jsmvvm

I'm thinking that my application is getting quite large now, too large to handle each View with a single ViewModel.

So I'm wondering how difficult it would be to create multiple ViewModels and load them all into a single View. With a note that I also need to be able to pass X ViewModel data into Y ViewModel data so the individual ViewModels need to be able to communicate with each other or at least be aware of each other.

For instance I have a <select> drop down, that select drop down has a selected state which allows me to pass the ID of the selected item in the <select> to another Ajax call in a separate ViewModel….

Any points on dealing with numerous ViewModels in a single View appreciated 🙂

Best Answer

Knockout now supports multiple model binding. The ko.applyBindings() method takes an optional parameter - the element and its descendants to which the binding will be activated.

For example:

ko.applyBindings(myViewModel, document.getElementById('someElementId'))

This restricts the activation to the element with ID someElementId and its descendants.

See documentation for more details.

Related Solutions

C# – How should the ViewModel close the form

I was inspired by Thejuan's answer to write a simpler attached property. No styles, no triggers; instead, you can just do this:

<Window ...
        xmlns:xc="clr-namespace:ExCastle.Wpf"
        xc:DialogCloser.DialogResult="{Binding DialogResult}">

This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place. Just put a bool? DialogResult property on your ViewModel and implement INotifyPropertyChanged, and voilà, your ViewModel can close the Window (and set its DialogResult) just by setting a property. MVVM as it should be.

Here's the code for DialogCloser:

using System.Windows;

namespace ExCastle.Wpf
{
    public static class DialogCloser
    {
        public static readonly DependencyProperty DialogResultProperty =
            DependencyProperty.RegisterAttached(
                "DialogResult",
                typeof(bool?),
                typeof(DialogCloser),
                new PropertyMetadata(DialogResultChanged));

        private static void DialogResultChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e)
        {
            var window = d as Window;
            if (window != null)
                window.DialogResult = e.NewValue as bool?;
        }
        public static void SetDialogResult(Window target, bool? value)
        {
            target.SetValue(DialogResultProperty, value);
        }
    }
}

I've also posted this on my blog.

Wpf – Multiple ViewModels associated with a single view

No that is fine; each object should be a ViewModel in its own right. It makes for cleaner code, nicer interactions, and remember, if it works well then it's correct (even if it violates guidelines).

I would do it exactly the way you are prescribing. I'd bind my grid to a Team, which would have an ObservableCollection<Player>, where Player is another ViewModel-type class. Each row item would get the Player as its DataContext and so you're still binding to ViewModel properties as you'd expect: and Player can still have public properties for ICommands (likely RelayCommands) for manipulation!

Hope that helps!

Best Answer

Related Solutions

C# – How should the ViewModel close the form

Wpf – Multiple ViewModels associated with a single view

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