Modifying Label inside run() method by Runnable

Question

Can someone help me with modifying Label inside the Runnable's run() method. I tried multiple times and always get this:

Exception in thread "pool-2-thread-1" java.lang.IllegalStateException: Not on FX application thread; currentThread = pool-2-thread-1

Answer 1

Any code that modifies visual components in JavaFX needs to be run from the JavaFX application thread -- it can't be run directly from a separate thread.

However, the separate thread (e.g. the Runnable you've created) can ask the JavaFX thread to run some code the next chance it gets. This is done using:

Platform.runLater(() -> { /* set label text or do other gui stuff here */ }).

Note: We did this in the early lab that involved having a separate thread causing the video to auto-play. We also used this code in the handleTrackedFrame(...) method that gets called by the AutoTracker's separate thread.