Continuing from using a canvas in tab item

Question

I asked about inserting a canvas into a tab item and ws given an answer which helped sort the problem , howvere i have hit another problem , the code is
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace WPFDynamicTab
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
        private List<TabItem> _tabItems;
        private TabItem _tabAdd;
        private Canvas canvas1;
        public MainWindow()
           try
                InitializeComponent();
                // initialize tabItem array
                _tabItems = new List<TabItem>();
                // add a tabItem with + in header
                _tabAdd = new TabItem();
                 canvas1= new Canvas();
                _tabAdd.Header = "+";
                _tabAdd.MouseLeftButtonUp += _tabAdd_MouseLeftButtonUp;
                _tabItems.Add(_tabAdd);
                this.AddTabItem();   // add first tab
                // bind tab control
                tabDynamic.DataContext = _tabItems;
                tabDynamic.SelectedIndex = 0;
            catch (Exception ex)
                MessageBox.Show(ex.Message);
        private TabItem AddTabItem()
            int count = _tabItems.Count;
            // create new tab item
            TabItem tab = new TabItem();
            tab.Header = string.Format("Tab {0}", count);
            tab.Name = string.Format("tab{0}", count);
            tab.HeaderTemplate = tabDynamic.FindResource("TabHeader") as DataTemplate;
            // add controls to tab item, this case I added just a canvas
            Canvas canvas = new Canvas();
            canvas.Name = "canvas";
            Canvas canvas1 = new Canvas();
            canvas1.Name = "canvas1";
            // defining the background color of "canvas"
            switch (count)
                case 0:
                    canvas.Background = Brushes.Green;
                    break;
                case 1:
                    canvas.Background = Brushes.Red;
                    break;
                case 2:
                    canvas.Background = Brushes.Blue;
                    break;
                case 3:
                    canvas.Background = Brushes.Yellow;
                    break;
                case 4:
                    canvas.Background = Brushes.Brown;
                    break;
                case 5:
                    canvas.Background = Brushes.Orange;
                    break;
                case 6:
                    canvas.Background = Brushes.Olive;
                    break;
                default:
                    break;
            // Canvas_Paint defines the background color of  "canvas1"
// XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
        //    tab.Content = canvas;     // ORIGINAL (commented out) to populate tab.Content with canvas
            Canvas_Paint();
            tab.Content = canvas1;      //  NEW to populate tab.Content with canvas
// XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
            // insert tab item right before the last (+) tab item
            _tabItems.Insert(count - 1, tab);
            return tab;
        private void _tabAdd_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
            TabItem newTab = this.AddTabItem();
            // clear tab control binding
            tabDynamic.DataContext = null;
            // bind tab control
            tabDynamic.DataContext = _tabItems;
            tabDynamic.SelectedItem = newTab;
        private void Canvas_Paint()
            int count = _tabItems.Count;
            switch (count)
                case 0:
                    canvas1.Background = Brushes.Green;
                    break;
                case 1:
                    canvas1.Background = Brushes.Red;
                    break;
                case 2:
                    canvas1.Background = Brushes.Blue;
                    break;
                case 3:
                    canvas1.Background = Brushes.Yellow;
                    break;
                case 4:
                    canvas1.Background = Brushes.Brown;
                    break;
                case 5:
                    canvas1.Background = Brushes.Orange;
                    break;
                case 6:
                    canvas1.Background = Brushes.Olive;
                    break;
                default:
                    break;
        private void tabDynamic_SelectionChanged(object sender, SelectionChangedEventArgs e)
and the xml is
<Window x:Class="WPFDynamicTab.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Dynamic Tab" Height="300" Width="527" WindowStartupLocation="CenterScreen">
    <Grid>
        <TabControl Name="tabDynamic" ItemsSource="{Binding}" SelectionChanged="tabDynamic_SelectionChanged">
            <TabControl.Resources>
                <DataTemplate x:Key="TabHeader" DataType="TabItem">
                    <DockPanel>
                        <TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType=TabItem }, Path=Header}" />
                    </DockPanel>
                </DataTemplate>
            </TabControl.Resources>
        </TabControl>
    </Grid>
</Window>
The problem is when i use the Canvas "canvas" with the canvas pouplated within the method  all is ok  , however using "canvas1" where canvas1 is populated in Canvas_Paint 
"canvas1" has null entries. How can I set the background colour in the tab using Canvas_Paint. Can the canvs be put in the XML? I hve simplified the problem from a much more complicated one in order to highlight the problem
steve

Answer 1

>>I asked about inserting a canvas into a tab item and ws given an answer which helped sort the problem , howvere i have hit another problem , the code is
Please close your previous threads by marking helpful posts as answer before starting a new one. And please only ask one question per thread.
>>How can I set the background colour in the tab using Canvas_Paint?
You never set the Background of the canvas1 that you create in the AddTabItem() and use as the Content of the TabItem. Just remove this line from this method:
Canvas canvas1 = new Canvas();
...and you will see the background:
private TabItem AddTabItem()
int count = _tabItems.Count;
// create new tab item
TabItem tab = new TabItem();
tab.Header = string.Format("Tab {0}", count);
tab.Name = string.Format("tab{0}", count);
tab.HeaderTemplate = tabDynamic.FindResource("TabHeader") as DataTemplate;
// add controls to tab item, this case I added just a canvas
Canvas canvas = new Canvas();
canvas.Name = "canvas";
canvas1.Name = "canvas1";
// defining the background color of "canvas"
switch (count)
case 0:
canvas.Background = Brushes.Green;
break;
case 1:
canvas.Background = Brushes.Red;
break;
case 2:
canvas.Background = Brushes.Blue;
break;
case 3:
canvas.Background = Brushes.Yellow;
break;
case 4:
canvas.Background = Brushes.Brown;
break;
case 5:
canvas.Background = Brushes.Orange;
break;
case 6:
canvas.Background = Brushes.Olive;
break;
default:
break;
// Canvas_Paint defines the background color of "canvas1"
// XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
//tab.Content = canvas; // ORIGINAL (commented out) to populate tab.Content with canvas
Canvas_Paint();
tab.Content = canvas1; // NEW to populate tab.Content with canvas
// XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
// insert tab item right before the last (+) tab item
_tabItems.Insert(count - 1, tab);
return tab;
Another approach bay be to pass the Canvas element to the painted to the Canvas_Paint() method by reference instead of using a class-level field:
Canvas_Paint(ref canvas1);
tab.Content = canvas1;
private void Canvas_Paint(ref Canvas canvas1)
int count = _tabItems.Count;
switch (count)
case 0:
canvas1.Background = Brushes.Green;
break;
case 1:
canvas1.Background = Brushes.Red;
break;
case 2:
canvas1.Background = Brushes.Blue;
break;
case 3:
canvas1.Background = Brushes.Yellow;
break;
case 4:
canvas1.Background = Brushes.Brown;
break;
case 5:
canvas1.Background = Brushes.Orange;
break;
case 6:
canvas1.Background = Brushes.Olive;
break;
default:
break;
Please remember to close your threads by marking helpful posts as answer and please start a new thread if you have a new question.