Why can't UI components be accessed from a backgroundworker?

Question

Threads all share resources. That\'s the whole problem around multi-threaded operations.

MSDN says:

You must be careful not to manipulate any user

Answer 1

It can be done with something as simple as having each control store the current thread (or maybe just its ID) in a private field in the constructor and then checking if the current thread is still that one before every method. Something like this:

class ThreadAffineObject
{
    private readonly Thread originalThread;
    public ThreadAffineObject()
    {
        this.originalThread = Thread.CurrentThread;
    }

    private void PreventCrossThreadOperation()
    {
        if(Thread.CurrentThread != originalThread)
            throw new CrossThreadOperationException();
    }

    public void DoStuff()
    {
        PreventCrossThreadOperation();
        // Actually do stuff
    }

    private int someField;
    public int SomeProperty
    {
        get { return someField; } // here reading is allowed from other threads
        set
        {
            PreventCrossThreadOperation(); // but writing isn't
            someField = value;
        }
    }
}