Question

I have a tab control bound to an observablecollection for dynamic tabs as follows:

<TabControl ItemsSource="{Binding AllTabs}" SelectedIndex="{Binding SelectedItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
        <TabControl.ItemTemplate>
            <DataTemplate>
                   <!--.............. -->
            </DataTemplate>
        </TabControl.ItemTemplate>

        <TabControl.ContentTemplate>
            <DataTemplate DataType="{x:Type vm:TabViewModel}">
                <c:MyTabItem/>
            </DataTemplate>
        </TabControl.ContentTemplate>
    </TabControl>

So, the tab headers and contents are defined dynamically and assigned as the observable collection changes. Now, I would like to hide some tabs without deleting them in the collection behind – in order to keep the data should the tab reopen.

Ideally, each chat tab viewmodel has a IsVisible property that is set to true by default. However, where do I bind such a property to in order to make a tab item collapse?

Answer 1

If you can modify your vm:TabViewModel I should change your IsVisible to a Visibility property and use the following ContentTemplate:

<TabControl.ContentTemplate>
    <DataTemplate DataType="{x:Type vm:TabViewModel}">
        <c:MyTabItem Visibility={Binding Visibility}/>
    </DataTemplate>
</TabControl.ContentTemplate>

Else you could use a converter to change the boolean IsVisible to an Visibility enum:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Data;
using System.Windows;

namespace Something.Converters
{
    [ValueConversion(typeof(bool), typeof(Visibility))]
    public class BoolToVisibilityConverter : IValueConverter
    {

        #region IValueConverter Members
        /// <summary>
        /// Converts a value.
        /// </summary>
        /// <param name="value">The value produced by the binding source.</param>
        /// <param name="targetType">The type of the binding target property.</param>
        /// <param name="parameter">The converter parameter to use.</param>
        /// <param name="culture">The culture to use in the converter.</param>
        /// <returns>
        /// A converted value. If the method returns null, the valid null value is used.
        /// </returns>
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value is bool && targetType == typeof(Visibility))
            {
                bool val = (bool)value;
                if (val)
                    return Visibility.Visible;
                else
                    if (parameter != null && parameter is Visibility )
                        return parameter;
                    else
                        return Visibility.Collapsed;
            }
            throw new ArgumentException("Invalid argument/return type. Expected argument: bool and return type: Visibility");
        }

        /// <summary>
        /// Converts a value.
        /// </summary>
        /// <param name="value">The value that is produced by the binding target.</param>
        /// <param name="targetType">The type to convert to.</param>
        /// <param name="parameter">The converter parameter to use.</param>
        /// <param name="culture">The culture to use in the converter.</param>
        /// <returns>
        /// A converted value. If the method returns null, the valid null value is used.
        /// </returns>
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value is Visibility && targetType == typeof(bool))
            {
                Visibility val = (Visibility)value;
                if (val == Visibility.Visible)
                    return true;
                else
                    return false;
            }
            throw new ArgumentException("Invalid argument/return type. Expected argument: Visibility and return type: bool");
        }
        #endregion
    }
}

Inculde the namespace in your xaml (your root element, Window in this example):

<Window xmlns:converters="clr-namespace:Something.Converters"
.../>

And in your resources:

<Window.Resources>
    <converters:BoolToVisibilityConverter x:Key="boolToVisibilityConverter"/>
</Window.Resources>

And finaly the binding:

<TabControl.ContentTemplate>
    <DataTemplate DataType="{x:Type vm:TabViewModel}">
        <c:MyTabItem Visibility={Binding IsVisible, Converter={StaticResource boolToVisibilityConverter}, ConverterParameter=Visibility.Collapsed}/>
    </DataTemplate>
</TabControl.ContentTemplate>

I think thats it 🙂

Edit: Ow and change the ConverterParameter to Visibility.Collapsed to Visibility.Hidden for hidden 😉