Java Android，如何在一定时间内动态改变一个TextView的背景色

Question

I have a List that consists of a boolean and an int. I want to dynamically change the background color between black and white of a TextView for a certain time of (int) numbers. I have treid this approach so far, however, when running the UI sleeps and the textView will only be updated once at the end.

       List<Primitive> codeContainer;
       codeContainer.add(new Primitive(3, true));
       codeContainer.add(new Primitive(1, false));
       codeContainer.add(new Primitive(7, true));
       theBlinker = findViewById(R.id.theBlinker);
       theBlinker.setBackgroundColor(ContextCompat.getColor(this, R.color.black));
       submit = findViewById(R.id.submit);

       submit.setOnClickListener(view -> {
           for (Primitive item : codeContainer) {
               blinking(item.getSignalLengthInDits() * 500);
           }
           theBlinker.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.black));
       });
}
   private void blinking(int time) {
       final Handler handler = new Handler();
       new Thread(() -> handler.post(() -> {
          theBlinker = findViewById(R.id.theBlinker);
           ColorDrawable buttonColor = (ColorDrawable) txt.getBackground();
           if (buttonColor.getColor() == Color.BLACK) {
               txt.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.white));
           } else {
               txt.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.black));
           }
           try {
               Thread.sleep(time);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
       })).start();
   }

Any Ideas?

Answer 1

I think you should use executors with handlers.

    //define executors and handlers
    static Executor mExecutor = Executors.newSingleThreadExecutor();
    final static Handler handler = new Handler(Looper.getMainLooper());

       List<Primitive> codeContainer;
       codeContainer.add(new Primitive(3, true));
       codeContainer.add(new Primitive(1, false));
       codeContainer.add(new Primitive(7, true));
       theBlinker = findViewById(R.id.theBlinker);
       theBlinker.setBackgroundColor(ContextCompat.getColor(this, R.color.black));
       submit = findViewById(R.id.submit);

       submit.setOnClickListener(v ->{
          //execute the task
           mExecutor.execute(() ->{
               for (Primitive item : codeContainer) {
                   blinking();

                   //after changing color sleeps the thread
                  try {
                    Thread.sleep(item.getSignalLengthInDits() * 500);
                  } catch (InterruptedException e) {
                    e.printStackTrace();
                  }
               }
               theBlinker.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.black));
           });
       });
}
    private void blinking() {

       //change text view color on the main thread
        handler.post(() -> {
            theBlinker = findViewById(R.id.theBlinker);
            ColorDrawable buttonColor = (ColorDrawable) txt.getBackground();
            if (buttonColor.getColor() == Color.BLACK) {
                txt.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.white));
            } else {
                txt.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.black));
            }
        });
    }

Answer 2

The problem is that you make the UI thread going to sleep. You should never ever do that!

This pauses the entire UI thread and therefore prevent it from doing anything (drawing, changing colors, input detection etc.).

There are several better ways to achieve what you want than with using Thread.Sleep (actually you need that almost never with android).

1. You only schedule the first change with new Handler().post(..) and from there schedule the next change with new Handler().postDelayed(..) (calling your method "recursively")
2. You schedule all the changes instantly with new Handler().postDelayed(..) , but for every new state, you add the delays of the previous ones (add a variable to your loop, that you increment with the current delay and use the sum for every next schedule).
3. If possible, you can use an animation with the keyframes set to your delay: read this article

There are of course more possibilities, but I think for your example these are suitable.

Btw. you don't need an extra thread, as it does nothing than scheduling a task on the UI thread and then die. new Handler().post(..) makes your task beeing executed after your current code is finished (and possibly other tasks, as it's added to the end of the internal task list).