Code

<StackPanel Orientation="Vertical" Margin="0,2,0,2">
                    <Button Margin="1" Padding="2" HorizontalContentAlignment="Left"
                            Style="{StaticResource ToolBarButtonBaseStyle}"
                            Command="{x:Static ApplicationCommands.Open}"
                            CommandTarget="{Binding ElementName=MyDesigner}">
                        <Button.Content>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition/>
                                    <ColumnDefinition/>
                                </Grid.ColumnDefinitions>
                                <Image Source="/Layout/Images/OpenFolder.png" Width="16"/>
                                <TextBlock Margin="3,0,3,0" Text="Open" VerticalAlignment="Center"  Grid.Column="1"/>
                            </Grid>
                        </Button.Content>
                    </Button> 

Code

public MainWindow()
{
   InitializeComponent();
   CommandBindings.Add(new CommandBinding(ApplicationCommands.New, New_Executed));
}

        private void New_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            flowchart.ClearAll();
        }