Accessing an array in xaml with enums

Question

I would like to be able to access an item from an ObservableCollection in XAML by using an enum.

I can bind to the ObservableCollection and specify which item in the XAML in the following way:

<Window x:Class="ArrayPropertyBinding.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:ArrayPropertyBinding"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:MyViewModel />
    </Window.DataContext>
    <StackPanel>
        <CheckBox Content="First" IsChecked="{Binding FilterBy[0],Mode=TwoWay}"/>
        <CheckBox Content="Second" IsChecked="{Binding FilterBy[1],Mode=TwoWay}"/>
        <CheckBox Content="Thrid" IsChecked="{Binding FilterBy[2],Mode=TwoWay}"/>
        <CheckBox Content="Fourth" IsChecked="{Binding FilterBy[3],Mode=TwoWay}"/>
        <Button Content="Print" Click="Button_Click_1"/>
        <Button Content="SetFourthTrue" Click="Button_Click_SetFourthTrue"/>
    </StackPanel>
</Window>

While the view model looks like this

public class MyViewModel
{
    public enum Filters
    {
        First = 0,
        Second,
        Thrid,
        Fourth
    }

    private ObservableCollection<bool> _filterBy = new ObservableCollection<bool>() { false, false, false, false };
    public ObservableCollection<bool> FilterBy
    {
        get { return _filterBy; }
    }

    public void PrintFilters()
    {
        System.Diagnostics.Debug.Write("<<<<");
        foreach (bool b in _filterBy)
        {
            System.Diagnostics.Debug.Write(b);
            System.Diagnostics.Debug.Write(" ");
        }
        System.Diagnostics.Debug.WriteLine(">>>>");
    }

    public void SetFourthTrue()
    {
        FilterBy[(int)Filters.Fourth] = true;
    }
}

I would like to be able to write the XAML as this:

<CheckBox Content="First" IsChecked="{Binding FilterBy[Filters.First],Mode=TwoWay}"/>

Any pointers or ideas would be greatly appreciated.

score 3 · Accepted Answer · edited May 23 '17 at 11:45

3

Probably boils down to custom binding path construction, as trying to enter an enum value directly does not appear to be possible.

Syntax then would be:

{Binding Path={me:PathConstructor FilterBy[(0)], {x:Static myns:Filters.First}}}

(Would recommend moving enums out of classes, otherwise it's myns:MyViewModel+Filters.First if i am not mistaken)

edited May 23 '17 at 11:45

Community

1
1

answered Jul 22 '13 at 18:24

H.B.

166,899
29
327
400

Awesome. +10 totally. – Federico Berasategui Jul 22 '13 at 18:31
Thanks H.B. this got me in the right direction. I have posted my updated code in my question. – AlC Jul 23 '13 at 12:22
@AIC: Please do *not* place answers in questions, please post it as your own answer as Q and A should be strictly separated. – H.B. Jul 23 '13 at 15:02

score 1 · Answer 2 · answered Jul 24 '13 at 00:51

So, this is what I have after H.B.'s answer. And it works well for me.

<StackPanel>
    <CheckBox Content="First" IsChecked="{Binding Path={local:PathConstructor FilterBy, {x:Static local:Filters.First}}}"/>
    <CheckBox Content="Second" IsChecked="{Binding Path={local:PathConstructor FilterBy, {x:Static local:Filters.Second}}}"/>
    <CheckBox Content="Thrid" IsChecked="{Binding FilterBy[2],Mode=TwoWay}"/>
    <CheckBox Content="Fourth" IsChecked="{Binding FilterBy[3],Mode=TwoWay}"/>
    <Button Content="Print" Click="Button_Click_1"/>
    <Button Content="SetFourthTrue" Click="Button_Click_SetFourthTrue"/>
</StackPanel>

And in the Code behind

public static class StringEnumConversion
{
    public static int ConvertToEnum<T>(object value)
    {
        Contract.Requires(typeof(T).IsEnum);
        Contract.Requires(value != null);
        Contract.Requires(Enum.IsDefined(typeof(T), value.ToString()));
        return (int)Enum.Parse(typeof(T), value.ToString());
    }
}

[ContentProperty("Parameters")]
public class PathConstructor : MarkupExtension
{
    public string Path { get; set; }
    public IList Parameters { get; set; }

    public PathConstructor()
    {
        Parameters = new List<object>();
    }

    public PathConstructor(string b, object p0)
    {
        Path = b;
        Parameters = new[] { p0 };
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return new PropertyPath(String.Format("{0}[{1}]",Path,StringEnumConversion.ConvertToEnum<Filters>(Parameters[0])));
    }
}

Accessing an array in xaml with enums

2 Answers2

Linked