WorldClockStatusWindow/SettingsWindow/TimeZoneWindow.xaml

<Window x:Class="WorldClockStatusWindow.SettingsWindow.TimeZoneWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:properties="clr-namespace:WorldClockStatusWindow.Properties"
        xmlns:worldClockStatusWindow="clr-namespace:WorldClockStatusWindow"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        d:DataContext="{d:DesignInstance Type=worldClockStatusWindow:TimeZoneEntry}"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
        xmlns:windows="clr-namespace:ChrisKaczor.Wpf.Windows;assembly=ChrisKaczor.Wpf.Windows.CategoryWindow"
        mc:Ignorable="d"
        Title="TimeZoneWindow"
        ResizeMode="NoResize"
        SizeToContent="Height"
        Width="450"
        WindowStartupLocation="CenterOwner"
        Icon="/WorldClockStatusWindow;component/Resources/Application.ico"
        FocusManager.FocusedElement="{Binding ElementName=LabelTextBox}">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.FlatButton.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Themes/light.cobalt.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid Margin="6">
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <StackPanel Margin="0,4"
                    windows:Spacing.Vertical="8">
            <TextBox Name="LabelTextBox"
                     mah:TextBoxHelper.UseFloatingWatermark="True"
                     mah:TextBoxHelper.Watermark="{x:Static properties:Resources.LabelColumnHeader}"
                     mah:TextBoxHelper.SelectAllOnFocus="True"
                     Text="{Binding Path=Label, UpdateSourceTrigger=Explicit, ValidatesOnExceptions=True}" />
            <ComboBox Name="TimeZoneComboBox"
                      DisplayMemberPath="DisplayName"
                      SelectedValuePath="Id"
                      SelectedValue="{Binding Path=TimeZoneId}"
                      VirtualizingPanel.IsVirtualizing="False"
                      mah:TextBoxHelper.UseFloatingWatermark="True"
                      mah:TextBoxHelper.Watermark="{x:Static properties:Resources.TimeZoneColumnHeader}" />
        </StackPanel>
        <StackPanel Grid.Column="0"
                    Grid.Row="1"
                    Orientation="Horizontal"
                    Margin="0,5,0,0"
                    HorizontalAlignment="Right">
            <Button Content="{x:Static properties:Resources.OkayButton}"
                    HorizontalAlignment="Right"
                    VerticalAlignment="Bottom"
                    Width="75"
                    Margin="0,0,5,0"
                    IsDefault="True"
                    Click="HandleOkayButtonClick">
                <Button.Style>
                    <Style TargetType="Button" BasedOn="{StaticResource {x:Type Button}}">
                        <Style.Triggers>
                            <DataTrigger Binding="{Binding Text.Length, ElementName=LabelTextBox}"
                                         Value="0">
                                <Setter Property="IsEnabled"
                                        Value="False" />
                            </DataTrigger>
                        </Style.Triggers>
                    </Style>
                </Button.Style>
            </Button>
            <Button Content="{x:Static properties:Resources.CancelButton}"
                    HorizontalAlignment="Right"
                    VerticalAlignment="Bottom"
                    Width="75"
                    IsCancel="True" />
        </StackPanel>
    </Grid>
</Window>