8.11. Multithreading SWT Applications
Problem
You’re running code in a worker thread, and you need to interact with the user interface in an SWT application.
Solution
Use the Display.getDefault
method to get access to
the main UI thread. Then use the asyncExec
or
syncExec
methods, passing them a
Runnable
object that will interact with user
interface elements.
Discussion
In an SWT application, the main thread,
called the UI
thread
, is the thread responsible for handling events and
dispatching them to widgets. In other GUI frameworks such as AWT or
Swing, you don’t have to interact with the UI thread
directly, but the SWT architecture is different (SWT uses a
message-pump architecture to support plug-ins in Eclipse).
If you’ve got a lot of intensive work to do, it isn’t a good idea to burden the UI thread, and you might want to launch a worker thread. On the other hand, the UI thread is the only thread that can interact with SWT user interface elements without throwing an exception.
So, how do you interact with user interface elements from worker
threads? You can use the UI thread’s
asyncExec
and syncExec
methods,
passing a Runnable
object that works with the user
interface element you want. Here’s an example. In
this worker thread code, we want to display some text in a text
widget. To do that, you get the current Display
object using the Display.getDefault
method and set
the text in the text widget like so:
Display.getDefault( ).asyncExec(new Runnable( ) { public void run( ) { textWidget.setText("Worker ...
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