Calling a method in WPF code behind which is not UI specific

Question

Am having a method

public void selectingTab(string name)
{
   //Code to select a particular tabitem in the XAML based on the parameter name
}`

in my WPF code behind and in my XAML page, i have a tab control.The parameter of the function specifies which tabitem should be brought to focus.And i want to call this method in a class file in the same solution. But when i try to call this method as NewChatWindow.selectingTab(clientName) am getting an error like object reference is required.When i try to create some object for the window and call the method like

NewChatWindow win = new NewChatWindow();
win.selectingTab(clientName);

Am getting the error "The calling thread must be STA, because many UI components" . How can i go about this.Thanks in advance.

@patrickmpls I want to call the function not in my XAML codebehind.In a seperate class file — Dhivya Sadasivam, Oct 19 '13 at 16:44
s i want to call the method inside a thread which is in some other class file — Dhivya Sadasivam, Oct 19 '13 at 16:50
Task.Factory.StartNew(() => {NewWindow.selectingTab(ClientName); using (var ns = cl.GetStream()) using (var br = new BinaryReader(ns)) using (var bw = new BinaryWriter(ns)) { Console.WriteLine("Message from client is " + br.ReadString() + " from " + clientName); } }); — Dhivya Sadasivam, Oct 19 '13 at 16:50
Any UI component in WPF should be created on Main thread. So, you need to delegate your call to Dispatcher. You can't access UI component from background thread. — Rohit Vats, Oct 19 '13 at 17:00

score 2 · Answer 1 · edited May 23 '17 at 10:31

2

There's TWO things going on here...

The UI thread cannot interact with activity originating in a different thread when controls are involved (such as your tab control). To avoid cross-threading problems, use a construct like this...

  private void DoSomethingOnTheUiThread()
        {
            Dispatcher.BeginInvoke((Action) (() =>
                {
                    // your code goes here...
                    Window w = new Window();
                    w.Show();
                }));
        }

...where the 'Dispatcher' gets the System.Windows.Threading.Dispatcher the window is associated with. Every UIElement has a dispatcher for this purpose. BeginInvoke schedules the delegate to run on the UI thread.

A related SO question gives more insight here: WPF Cross Thread Object Access

...and here How to deal with cross-thread access exceptions?

For your other issue, let's look at your code...

Task.Factory.StartNew(() => 
{
   NewWindow.selectingTab(ClientName); 
   using (var ns = cl.GetStream()) 
   using (var br = new BinaryReader(ns)) 
   using (var bw = new BinaryWriter(ns)) 
   { 
      Console.WriteLine("Message from client is " + br.ReadString() + " from " + clientName); } });

In your commentary you point out that 'NewWindow' is a class. But you are calling an instance method of 'NewWindow', not a static method of 'NewWindow'. So the compiler has complained about it.

To call an instance method, you must first create an instance, like this...

NewWindow nw = new NewWindow();
nw.selectedTab("some name");

The c# forefathers made the syntax 'NewWindow.selectedTab' to mean a static method. I don't know which of these you want to implement, but you'll need to pick one that is consistent with your usage.

Relevant docs are here: http://msdn.microsoft.com/en-us/library/aa645766(v=vs.71).aspx

**

When a method is referenced in a member-access (Section 7.5.4) of the form E.M, if M is a static method, E must denote a type containing M, and if M is an instance method, E must denote an instance of a type containing M.

**

edited May 23 '17 at 10:31

Community

1
1

answered Oct 19 '13 at 17:02

Gayot Fow

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so you mean i cant cal the method in another thread even if i use the code yo specified ? – Dhivya Sadasivam Oct 19 '13 at 17:06
Am new to this environment.So i dono much about delegates.Sorry if my questions looks stupid – Dhivya Sadasivam Oct 19 '13 at 17:07
Put all the relevant code where the above comment indicates and you'll be fine. – Gayot Fow Oct 19 '13 at 17:10
My question is how to call the method in some other class file.Am I reaching you the correct way ? my problem is not about making the tabitem to come to focus rather how do i pass the tabcontrol name from one class file to the codebehind – Dhivya Sadasivam Oct 19 '13 at 17:13
The 'calling thread' is the background thread you started. The string containing the name of the tab isn't affected. Try it! – Gayot Fow Oct 19 '13 at 17:19
you mean in the comment part i should put my thread code ? or the call of the function ? – Dhivya Sadasivam Oct 19 '13 at 17:23
You're starting to get it. In the comment part should be the stuff you want executed on the UI thread. Such as NewChatWindow win = new NewChatWindow(); win.selectingTab(clientName); etc etc – Gayot Fow Oct 19 '13 at 17:26
Am still getting the error at the BeginInvoke part.Its still showing like object reference is required for the non static field – Dhivya Sadasivam Oct 19 '13 at 17:30
Well? Are you attempting this from a static class or static method? – Gayot Fow Oct 19 '13 at 17:40
Nope :(...Am having the call in a simple .cs file only.And my method lies inside the NewWidow codebehind – Dhivya Sadasivam Oct 19 '13 at 17:49
where do i call tat dispatcher then ? – Dhivya Sadasivam Oct 20 '13 at 12:34

score 0 · Answer 2 · edited May 23 '17 at 12:05

I am assuming that you are using reflection to obtain the property information during runtime. You may be getting the object reference required error by how you are calling the instance method (Object reference is required for the nonstatic field method or property). Until you include the code that you have omitted, we can only guess as to why this error occurred.

If you want to reference an object in the XAML, you need an x:Name directive (The x:Name directive in WPF).

Here's an example of the WPF part:

<StackPanel DockPanel.Dock="Right" Background="Yellow" MinWidth="150" Margin="2" x:Name="StackPanelRight"></StackPanel>

Then, you can reference your named attribute from your code-behind.

        StackPanel sp = new StackPanel();
        StackPanel btnSP = new StackPanel();
        btnSP.Orientation = Orientation.Horizontal;
        btnSP.HorizontalAlignment = System.Windows.HorizontalAlignment.Center;
        btnSP.Children.Add(btn3);
        btnSP.Children.Add(btn4);
        sp.Children.Add(btnSP);
        StackPanelRight.Children.Add(sp);

STA stands for Single-Threaded Apartment. STA was coined during the COM days (Understanding The COM Single-Threaded Apartment ). Assuming your threading is asynchronous, this article may help you: Best practices in asynchronous programming.

I think i explained the question in a reverse way.All i need is am having a method in the XAML code behind all i want is to call the method from another .cs file tats all. — Dhivya Sadasivam, Oct 19 '13 at 17:17
I'm not sure that I understand what you mean by this: "All i need is am having a method in the XAML code behind all i want is to call the method from another .cs file tats all." What do you mean by "a method in the XAML code behind"? — devinbost, Oct 21 '13 at 00:38

score 0 · Answer 3 · edited May 23 '17 at 11:57

0

In order to utilize WPF functionality and benefits I would suggest using the MVVM pattern. From a model notification the UI can be modified (the required tab selected) event if a background thread initiates the change.

More about the MVVM pattern: This thread

edited May 23 '17 at 11:57

Community

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answered Oct 19 '13 at 17:14

Daniel Leiszen

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Calling a method in WPF code behind which is not UI specific

3 Answers3