code: void startAnimation() {
          if (getVisibility() != VISIBLE) {
              return;
          }
  
          if (mIndeterminateDrawable instanceof Animatable) {
              mShouldStartAnimationDrawable = true;
              mAnimation = null;
          } else {
              if (mInterpolator == null) {
                  mInterpolator = new LinearInterpolator();
              }
  
              mTransformation = new Transformation();
              mAnimation = new AlphaAnimation(0.0f, 1.0f);
              mAnimation.setRepeatMode(mBehavior);
              mAnimation.setRepeatCount(Animation.INFINITE);
              mAnimation.setDuration(mDuration);
              mAnimation.setInterpolator(mInterpolator);
              mAnimation.setStartTime(Animation.START_ON_FIRST_FRAME);
          }
          postInvalidate();
      }
docs: <p>Start the indeterminate progress animation.</p>