从后台线程和线程中的线程更新UI

Question

I have following Application Structure:

public partial class MainWindow : Window
{
    // Methos to update the TextBlock
    public void updateTextBlock(string txt)
    {
        this.myTextBlock.Text += txt;
    }        

    private void startThreadBtn_Click(object sender, RoutedEventArgs e)
    {
        // Start Thread1 here 
        Thread1 thread1 = new Thread1();
        new Thread(new ThreadStart(thread1.doSomthing)).Start(); 
    }
}

class Thread1
{
    public void doSomthing()
    {
        // ------------------------------
        // Update myTextBlock from here 
        // ------------------------------

        // Thread2 starts here 
        Thread2 thread2 = new Thread2();
        new Thread(new ThreadStart(thread2.doSomthing)).Start(); 
    }
} 

class Thread2
{
    public void doSomthing()
    {
        // ------------------------------
        // Update myTextBlock from here 
        // ------------------------------
    }
}

From both of these threads Thread1 and Thread2 classes I want to update the TextBlock which is in the MainWindow .

I have seen following solutions, and don't find this condition covered in this questions, also i am beginner and find it way difficult to understand.

• How to update UI from another thread running in another class
• How to update the GUI from another thread in C#?
• Update UI from background Thread

I can use solutions provided in the above questions for Thread1 but what about updating UI from Thread2 .
I am using .NET framework 4.5.
What is the best way of doing it.

Answer 1

…thread within a thread…

It appears that you have some misconceptions about what threads are. Let's look at these:

• Threads are not executed "within" one another. They are not nested. It is more accurate to think of threads as being executed "side-by-side".

  It doesn't matter how and where you started the second thread. It's simply a thread, just like your first thread, so when you want to update the UI from within one of these (non-UI) threads, you do exactly the same thing in both cases: schedule your UI update code on the UI thread, which is done in WPF via the Dispatcher.Invoke or Dispatcher.InvokeAsync methods.

   myTextBlock.Dispatcher.Invoke(() => { … /* update myTextBlock here */ }); // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ // this will be scheduled on the correct (UI) thread 

  See also: How do I get the UI thread Dispatcher?

• Threads are not the same as your Thread1 and Thread2 objects. Think of a thread as representing an execution path through your code; or a method that is executed on its own, if you prefer. A thread has an entry point (a method, represented by a ThreadStart delegate), which is where its execution starts, and the thread terminates when it reaches the end of that thread.

   class Thread1 { … void doSomthing() { … Thread2 thread2 = new Thread2(); new Thread(new ThreadStart(thread2.doSomthing)).Start(); } } 

  Even though you named your classes Thread1 and Thread2 , that does not make them threads. They are regular .NET classes that happen to contain the methods used as your threads' entry points. Threads are represented only by the Thread class (and take note that your classes do not, and could not, inherit from Thread ). And again, it doesn't matter where you happen to .Start() them; they are independent from one another.

• When you have something like this:

   class A { … } class B { void Foo() { var a = new A(); … } 

  B only takes a part in where and when an instance of A gets created , but it doesn't determine "where" A is . (Classes do not really have a location, anyway.) So it is wrong to say that " A is within B ". (The type A is referred to by a method of B , and a refers to an object instance that got created during the execution of an instance method of B , but it is still completely independent from B .)

---

Update: Concerning your added question below about how to make myTextBlock known to your threads, there are two solutions:

1. Either move both doSomthing methods into the MainWindow class (and give them unique names).

2. Pass myTextBlock to your Thread1 and Thread2 objects:

    class Thread1 { public Thread1(TextBlock textBlockToBeUpdated) { this.textBlock = textBlock; } private readonly TextBlock textBlock; void doSomthing() { textBlock.Dispatcher.Invoke(() => { /* update textBlock here */ }); } } … class MainWindow { … void startThreadBtn_Click(…) { Thread1 thread1 = new Thread1(myTextBlock); // <-- … } }