获取资源字典的控件模板的控件实例方法

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:JetSun.Presentation" 
    xmlns:js="clr-namespace:JetSun.Presentation.Markups">
    <Style TargetType="local:MessageBoxControl">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="local:MessageBoxControl">
                    <Grid FlowDirection="{Binding ContentFlowDirection}" MaxWidth="600">
                        <Grid.RowDefinitions>
                            <RowDefinition Height="55" />
                            <RowDefinition Height="*" />
                            <RowDefinition Height="*" />
                            <RowDefinition Height="auto" />
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>

                        <Image Source="{Binding MessageImageSource}" HorizontalAlignment="Left" VerticalAlignment="Center" Height="32" Width="32" Margin="10 0 0 0" />

                        <TextBlock Text="{Binding Message}" Grid.RowSpan="2" Grid.Column="1" TextWrapping="Wrap" TextAlignment="Left" HorizontalAlignment="{Binding ContentTextAlignment}" VerticalAlignment="Center" Margin="10 10 10 10" />

                        <Border Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2" BorderThickness="0 1 0 0" Margin="3">
                            <StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0 0 5 0" >
                                <Button Content="是" Visibility="{Binding YesNoVisibility}" Command="{Binding YesCommand}" IsDefault="{Binding IsYesDefault}" Margin="5 5 5 5"   Width="80" x:Name="PART_YesButton" IsTabStop="True" TabIndex="0"/>
                                <Button Content="否" Visibility="{Binding YesNoVisibility}" Command="{Binding NoCommand}" IsDefault="{Binding IsNoDefault}" Margin="5 5 5 5"  Width="80" x:Name="PART_NoButton" IsTabStop="True" TabIndex="1" />
                                <Button Content="确认" Visibility="{Binding OkVisibility}" Command="{Binding OkCommand}" IsDefault="{Binding IsOkDefault}" Margin="5 5 5 5" Width="80" x:Name="PART_OkButton" IsTabStop="True" TabIndex="2" />
                                <Button Content="取消" Visibility="{Binding CancelVisibility}" Command="{Binding CancelCommand}" IsDefault="{Binding IsCancelDefault}" Margin="5 5 5 5"  Width="80" x:Name="PART_CancelButton" IsTabStop="True" TabIndex="3" />
                            </StackPanel>
                        </Border>
                    </Grid>

                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

    public class MessageBoxControl : Control
    {
        static MessageBoxControl()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(MessageBoxControl), new FrameworkPropertyMetadata(typeof(MessageBoxControl)));
        }

        Button _btnYes;
        Button _btnNo;
        Button _btnOk;
        Button _btnCancel;
        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();

            _btnYes = GetTemplateChild("PART_YesButton") as Button;
            _btnNo = GetTemplateChild("PART_NoButton") as Button;
            _btnOk = GetTemplateChild("PART_OkButton") as Button;
            _btnCancel = GetTemplateChild("PART_CancelButton") as Button;
        }

        protected override void OnGotFocus(RoutedEventArgs e)
        {
            MessageBoxViewModel model = this.DataContext as MessageBoxViewModel;
            if (model.IsYesDefault) { _btnYes.Focus(); }
            if (model.IsNoDefault) { _btnNo.Focus(); }
            if (model.IsOkDefault) { _btnOk.Focus(); }
            if (model.IsCancelDefault) { _btnCancel.Focus(); }
        }
    }