Java paintComponent tell if called again

问题

Been Googling for a few days and I can't figure out how to tell if paintComponent is being called while I'm processing paintComponent. The process is long and complicated. If I have a second (or third) request to paint, I want to abort the current paint process and start over with the most recent request.

回答1:

You can't; calls to paintComponent() are queued, blocking the EDT until completed. Use the approach shown in this AnimationTest to self-time your implementation on a typical target platform. Optimize as required. As a concrete example, this KineticModel illustrates several animation techniques that may apply to your use case.

Addendum: Your update suggests that the "long and complicated" process involves constructing a BufferedImage for later display. To avoid blocking the EDT, do this in the background of a SwingWorker from which you can publish() interim results as they become available. This example simulates building a raster image one line at a time.

This related example constructs a TexturePaint in a similar manner.

For specific guidance, edit your question to include a Minimal, Complete, and Verifiable example that shows your revised approach.

回答2:

As usual, I think of a solution after asking for one... My solution is to launch a thread that progressively updates a BufferedImage. Then, the paintComponent method is just two lines:

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(myImage, 0, 0, null);
}

The image is drawn very quickly. Calling super is required to erase the existing view of the image before redrawing it.

The rest of the solution is creating a thread that updates the myImage attribute of the panel. In my work, the image takes about 30 minutes to process completely, depending on the input to the program. It isn't a big deal unless I drag the window or accidentally touch the mouse wheel while the application is running. Then, paintComponent is called again and hangs the program. With this solution, the update can take days and you can resize or move the window all you want. You keep seeing the image as it has been processed so far.

来源：https://stackoverflow.com/questions/39534039/java-paintcomponent-tell-if-called-again