private void maybeOnFadeStarted() {
    if (mIsFadingActualImage) {
      return;
    }

    if (mActualImageLayer < 0 || mActualImageLayer >= mIsLayerOn.length) {
      return;
    }
    if (!mIsLayerOn[mActualImageLayer]) {
      return;
    }

    mIsFadingActualImage = true;

    if (mOnFadeListener != null) {
      mOnFadeListener.onFadeStarted();
    }
  }
Gets the transition state (STARTING, RUNNING, NONE). Useful for testing purposes.

@return transition state
drawee/src/main/java/com/facebook/drawee/drawable/FadeDrawable.java