如何在Android中动画子字符串？

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="16sp"
    android:textColor="@android:color/black"
    android:text="This is a sample text" />

TextView textView = findViewById(R.id.textView);
SpannableString spannableString = new SpannableString("This is a sample text");

ForegroundColorSpan colorSpan = new ForegroundColorSpan(Color.RED);
spannableString.setSpan(colorSpan, startIndex, endIndex, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

ValueAnimator animator = ValueAnimator.ofObject(new ArgbEvaluator(), Color.RED, Color.BLUE);
animator.setDuration(2000);
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        int animatedValue = (int) animation.getAnimatedValue();
        colorSpan.setForeColor(animatedValue);
        textView.setText(spannableString);
    }
});
animator.start();