Binding to a method with parameter in XAML using polymorphism in ViewModel

Question

I have a TabControl with six tabs in my ResultView. The ViewModel that sits behind this View can be either a ResultTypeOneViewModel or ResultTypeTwoViewModel, each of which derives from ResultViewModel but you can interchangeably use the result viewer with either result type.

The difference is that in ResultTypeOneViewModel, tabs 1 & 3 need to be visible and the rest hidden. In ResultTypeTwoViewModel, tabs 2, 3, 4, 5, 6 need to be visible and tab 1 hidden.

I wanted to do this via something like

<TabItem Name="1" Visibility={Binding IsTabVisible(0)}>
<TabItem Name="2" Visibility={Binding IsTabVisible(1)}>
<TabItem Name="3" Visibility={Binding IsTabVisible(2)}>
etc...

And have an abstract method declaration in ResultsViewModel such as

public abstract Visibility IsTabVisible(int index);

And in ResultsOneViewModel have

public override Visibility IsTabVisible(int index)
{
    if (index == 0 || index == 2) return Visibility.Visible;
    return Visibility.Hidden;
}

And in ResultsTwoViewModel have

public override Visibility IsTabVisible(int index)
{
    if (index == 0) return Visibility.Hidden;
    return Visibility.Visible;
}

But I cannot figure out how to call a method like this with a parameter through bindings iN WPF XAML.

Can anyone suggest how I can do this or if it's not possible via this method, another way I could solve this problem?

you're doing it all wrong. Create an `ObservableCollection` and bind your `TabControl.ItemsSource` to that. then create a `bool IsVisible` value in the ViewModel and bind the `Visibility` of the Tab Items to that using a `BoolToVisibilityConverter`. — Federico Berasategui, Nov 14 '13 at 14:49
Visibility is purely UI (WPF), and has no mean for ViewModel. Change it for Boolean, and use BooleanToVisibilityConverter in binding. — Xaruth, Nov 14 '13 at 14:51
HighCore, good idea to do it like that, Ive created a BaseResultViewModel class that I have an OBservableCollection of and binding that to the ItemsSource property of the TabControl. Problem is, the TabItem needs Header, HeaderStyle, Content properties etc. How do I get the ViewModel to provide all the dependency properties eg Header, Style, Content to the TabControl? — NZJames, Nov 14 '13 at 16:13

score 12 · Answer 1 · edited May 23 '17 at 12:16

To answer your question directly, you can use the ObjectDataProvider to call a method for you so you can work with the results:

xmlns:System="clr-namespace:System;assembly=mscorlib"
xmlns:Windows="clr-namespace:System.Windows;assembly=PresentationCore"

...

<Window.Resources>
    <ObjectDataProvider x:Key="IsTab1VisibleMethod" 
        ObjectType="{x:Type Windows:Visibility}" IsAsynchronous="True" 
        MethodName="IsTabVisible">
        <ObjectDataProvider.MethodParameters>
            <System:Int32>0</System:Int32>
        </ObjectDataProvider.MethodParameters>
    </ObjectDataProvider>
</Window.Resources>

You should then be able to access the result like this (but you'd need one of these for each TabItem):

<TabItem Visibility="{Binding Source={StaticResource IsTab1VisibleMethod}}" />

However, it's generally not good practice to manipulate UI properties such as Visibility in code, so a better idea would be to use a BooleanToVisibilityConverter to Bind the Visibility properties to bool values as @Highcore suggested. You can see an example of this in the Binding a Button Visibility to bool value in ViewModel post here on StackOverflow.

In my opinion, an even better solution would be to simply provide one view for every view model.

Is there a way to do two way data binding with a parameter similar to this? This looks like it would only work for setting the value in the element from the method but I'd like two way binding. I wonder if I have a design problem since I'm in this situation... — Skystrider, Jun 21 '16 at 22:58
Oh I guess the way to do it is with a converter that can convert back too. I think... — Skystrider, Jun 21 '16 at 23:01
@Skychan, it depends what you mean by parameter. You could probably just wrap it in a property and simply data bind to it. — Sheridan, Jun 22 '16 at 07:54
Thanks. Whatever it was I was trying to do that was similar to this, I got it to work. I think it ended up being a simple data bind to a property. — Skystrider, Jul 14 '16 at 21:19

score 3 · Answer 2 · edited Aug 18 '14 at 16:38

3

A better suggestion to this question is to use style.DataTrigger in style of TabItem like this:

<TabItem>
    <TabItem.Style>
        <Style target="{x:Type TabItem}">
            <Style.DataTriggers>
                <DataTrigger Binding="{Binding IsTabVisible}" Value="False">
                    <Setter Property="Visibility" Value = "Collapsed"/>
                </DataTrigger>
            </Style.DataTrigers>
        </Style>
    <TabItem.Style>
</TabItem>

edited Aug 18 '14 at 16:38

Zack

2,789
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answered Jul 02 '14 at 11:02

Enzojz

863
2
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Where do you pass the parameter to IsTabVisible() ? – Cédric Bourgeois Jan 29 '19 at 09:06
It's a boolean property. – Enzojz Jan 30 '19 at 11:13

score 2 · Answer 3 · answered Jan 14 '20 at 10:42

You can use an indexer property to be able to pass a single parameter to a property. Although it's probably not very intuitive to return a boolean value from an indexer property it works fine for me. Also keep in mind the indexer property looses it's expected functionality.

    class MyClass
    {
        public bool this[int tabNumber]
        {
            get
            {
                // Do logic to determine visibility here or in a separate method
                return IsTabVisible(tabNumber);
            }
        }

        bool IsTabVisible(int tabNumber)
        {
            bool result;

            // Method logic...

            return result;
        }
    }

So in XAML you can use the class name and provide a parameter between square brackets.

<TabItem Visibility="{Binding MyClass[0]}}"/>

If you need to raise a NotifyPropertyChanged for the indexer property use:

    NotifyPropertyChanged("Item[]");

I don't know if this fits into the MVVM pattern but it could be useful for anyone who wants to bind to a method with a single parameter.

This is indeed a hack and WPF may complain "MyClass is not a collection", but I've found it useful. It should only be used in very isolated, specific use-cases, though. — mike, Jan 07 '22 at 23:54

Binding to a method with parameter in XAML using polymorphism in ViewModel

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