如何在可运行文件中绘制 bitmap？

Question

I want to draw bitmap in runnable but dont work. The code gives an exit error from the application. I commented the non-working part in the code.

 private Runnable updateTimerThread = new Runnable() {

        public void run() {


                // This code block dont run. Application exit error.
                bitmap = Bitmap.createBitmap(500, 500, Bitmap.Config.ARGB_8888);
                Canvas canvas = new Canvas(bitmap);
                paint = new Paint(Paint.ANTI_ALIAS_FLAG);
                paint.setColor(Color.RED);
                rect = new RectF(0, 0, canvas.getWidth(), canvas.getHeight());
                canvas.drawArc(rect, 0F, 360F, true, paint);
                imageView.setImageBitmap(bitmap);
                imageView.invalidate();

                customHandler.postDelayed(this, showTime);
   

                timeSwapBuff += timeInMilliseconds;
                customHandler.removeCallbacks(updateTimerThread);
            
         }
    };

Answer 1

Submit your Runnable to an ExecutorService

Your question is not clear. But taking your question as written, I'll guess you neglected to call upon the code shown. A Runnable does not magically execute itself. You must submit an instance of your Runnable to an executor service.

Given the variable name updateTimeThread , I am guessing you want this code to run repeatedly on a background thread. So we need a scheduled executor service to run repeatedly.

That name shows some confusion on your part. A Runnable is not a thread. A Runnable is a task to be executed by an ExecutorService on one of its managed threads.

Let's define a simpler runnable to get some rudimentary code up and running.

Runnable task = new Runnable() {
    public void run() {
        System.out.println( "Running the run method at " + Instant.now() ) ;
    }
}

Establish your executor service.

ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor() ;

Submit an instance of your Runnable to be run every so often.

long delay = 0 ; 
long period = 1 ;
ses.scheduleAtFixedRate( task , delay , period , TimeUnit.SECONDS ) ;

Be sure to eventually shut down your executor service. Otherwise its backing thread pool may continue to run indefinitely, like a zombie ♂️.

And as with nearly all GUI toolkits, in Android never access the UI widgets from a background thread. Do calculations on the background thread. But when it comes time to update the UI use whatever mechanism is provided to ask the UI thread to run some code to update the UI widgets. (I don't know Android's mechanism.)