Do I have to lock the slider value in multithreading?

See more:

C#

WPF

threads

In a multiple threading WPF application, I want to update a slider value in a task.

Dispatcher.BeginInvoke((Action)delegate()
{
   if (remainder.CallMethod == "Test")
       slider1.Value = slider1.Value - 1;
}

The problem is each thread can access the above code, I did not use lock

lock(Object)
{
  Dispatcher.BeginInvoke((Action)delegate()
   {
     if (remainder.CallMethod == "Test")
       slider1.Value = slider1.Value - 1;
   }  
}

The result seems to be okay without lock, but do I have to use it?