Stop ContentTemplate Selector invoke on TabControl selection change event

Question

I have a TabControl. Each tab Item i.e newly added Tab is rendered using content template selector. But each time i switch between the tabs, content template selector is getting called.

I wanted to stop this. This is because, In the in Tabcontrol, User have provided actions to change the layout, since in the selection change event of the tab Item content template is getting called, it is getting difficult for me to retain the layout what user has changed during Tab Item Selection change Event.

Following is code i am using for the TabControl

UPDATE : I have created a sample project to explain my problem. Could not share the project anywhere, so updating the code snippet in main question. sorry for that.

In the sample project, user can add TabItem dynamically to TabControl. Eash Tabcontent can show two Grid panel and they are separated by Grid Splitter. Display of second grid is Based on some flag (in this example ShowSecondPanel). If user click on "Show / Hide Second Panel" button, then second panel content will be shown for the current selected tab.

The Problem is, user can re-size the panels using Grid Splitter, but when user navigates to some other tab and comes back to previous one, the grid splitter position changes to original position.

Hope I am clear on describing the problem.

Code for MainWindow.xaml

     

    


    
    
        
            
        
    
    
        
            
                
                
            
            
                
                
            
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Code For MainWindowViewModel

     using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Windows.Input;
    using System.ComponentModel;
    using System.Collections.ObjectModel;

     namespace TabControlTestApp
   {
class MainWindowViewModel : INotifyPropertyChanged
{
    public MainWindowViewModel()
    {
        this.loadTabCommand = new LoadTabCommand(this);
        tabContentList = new ObservableCollection();
    }

    public ICommand LoadTabCommand
    {
        get
        {
            return this.loadTabCommand;
        }
        set
        {
            this.loadTabCommand = value;
        }
    }

    public ObservableCollection TabContentList
    {
        get
        {
            return tabContentList;
        }
        set
        {
            tabContentList = value;
            OnPropertyChanged("TabContentList");
        }
    }

    public TabContent SelectedTabItem
    {
        get
        {
            return selectedTabItem;
        }
        set
        {
            selectedTabItem = value;
            OnPropertyChanged("SelectedTabItem");
        }

    }

    public void LoadFirstTab()
    {
        TabFirstPanel firstPanel = new TabFirstPanel() { Name = "John-1", Age = "31" };
        TabSecondPanel secondPanel = new TabSecondPanel() { AdditionalDetails="Some Details for First Tab" };
        TabContent firstTabContent = new TabContent() { TabFirstPanel = firstPanel, TabSecondPanel = secondPanel, ShowSecondPanel = false };
        tabContentList.Add(firstTabContent);
        SelectedTabItem = firstTabContent;
    }
    public void LoadSecondTab()
    {
        TabFirstPanel firstPanel = new TabFirstPanel() { Name = "John-2", Age = "31" };
        TabSecondPanel secondPanel = new TabSecondPanel() { AdditionalDetails = "Some Details for second Tab" };
       TabContent secondTabContent= new TabContent() { TabFirstPanel = firstPanel, TabSecondPanel = secondPanel, ShowSecondPanel=false };
       tabContentList.Add(secondTabContent);
       SelectedTabItem = secondTabContent;
    }
    public void LoadThirdTab()
    {
        TabFirstPanel firstPanel = new TabFirstPanel() { Name = "John-3", Age = "31" };
        TabSecondPanel secondPanel = new TabSecondPanel() { AdditionalDetails = "Some Details for Third Tab" };
        TabContent ThirdTabContent = new TabContent() { TabFirstPanel = firstPanel, TabSecondPanel = secondPanel, ShowSecondPanel = false };
        tabContentList.Add(ThirdTabContent);
        SelectedTabItem = ThirdTabContent;
    }

    public void ShowHideSecondPanelInTab()
    {
        TabContent currentTabContent = SelectedTabItem;   
        int currentIndex = tabContentList.IndexOf(SelectedTabItem);

        if (currentTabContent.ShowSecondPanel)
        {
            currentTabContent.ShowSecondPanel = false;
        }
        else
        {
            currentTabContent.ShowSecondPanel = true;
        }
        TabContentList.RemoveAt(currentIndex);
        TabContentList.Insert(currentIndex, currentTabContent);
        OnPropertyChanged("TabContentList");
        SelectedTabItem = currentTabContent;
    }

    private TabContent selectedTabItem = null;

    private ObservableCollection tabContentList = null;

    private ICommand loadTabCommand = null;


    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

}

Code for TabContentTemplateSelector.cs

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

      namespace TabControlTestApp
   {
class TabContentTemplateSelector : DataTemplateSelector
{
    public override System.Windows.DataTemplate SelectTemplate(object item, System.Windows.DependencyObject container)
    {
        FrameworkElement element = container as FrameworkElement;
        if (element != null && item != null)
        {
            TabContent tabContent = (TabContent)item;
            if (tabContent.ShowSecondPanel)
            {
                return element.FindResource("TabContentWithBothPanel") as DataTemplate;
            }
            else
            {
                return element.FindResource("TabContentWithFirstPanel") as DataTemplate;
            }
        }
        else
        {
            return base.SelectTemplate(item, container);
        }
    }
}

}

Code for TabContent Data Object

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

  namespace TabControlTestApp
  {
class TabFirstPanel
{
    public string Name { get; set; }

    public string Age { get; set; }
}

class TabSecondPanel
{
    public string AdditionalDetails { get; set; }
}

class TabContent
{
    public TabFirstPanel TabFirstPanel { get; set; }

    public TabSecondPanel TabSecondPanel { get; set; }

    public bool ShowSecondPanel { get; set; }
}

}

Code for LoadTabCommand Class

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

     namespace TabControlTestApp
       {
class LoadTabCommand : ICommand
{
    MainWindowViewModel mainWindowViewModel = null;

    public LoadTabCommand(MainWindowViewModel mainWindowViewModel)
    {
        this.mainWindowViewModel = mainWindowViewModel;
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        System.Windows.Controls.Button btn = (System.Windows.Controls.Button)parameter;
        switch (btn.Name)
        {
            case "LoadTab1":
                mainWindowViewModel.LoadFirstTab();
            break;
            case "LoadTab2":
            mainWindowViewModel.LoadSecondTab();
            break;
            case "LoadTab3":
            mainWindowViewModel.LoadThirdTab();
            break;
            case "ShowHideSecondPanelInTab":
            mainWindowViewModel.ShowHideSecondPanelInTab();
            break;
        }
    }
}

}

dev hedgehog · Accepted Answer

I took a look at your example. Thanks for posting code. Now I understand your issue completely. Before I suggested to change DynamicResource to StaticResource I thought you wanted to only look up once for your DataTemplate.

Now I see you wish to keep the instance of DataTemplate alive so TabControl doesn't destroy it when changing tabs.

Here is the solution:


    



    

    
        
            
        
    

    
        
            
            
        
        
            
            
        
        Name :
        
    

    
        
            
        
        
            
            
            
        
        
            
                
                
            
            
                
                
            
            Name :
            
        
        
        
            
                
                
            
            
                
                
            
            Additional Detail :

If you just copy past that you will do fine.

By the way, just as sidenote for you, destroying and building up DataTemplates is very important in wpf for releasing unmanaged memory.

Stop ContentTemplate Selector invoke on TabControl selection change event

Answers (2)

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