//加载当前index以及向前向后三张大图
    @Override
    public void loadCurrentLargeBitmap() {
        for(int i = mCurrentIndex - 1; i < mCurrentIndex + 2; i++){
            if(i >= 0 && i < mImagesCnt - 1){
                mBitmapCache.getLargeBitmap(mAllImagePaths[i]);
            }
        }
    }

    //index向前移动一位
    @Override
    public void rollForward() {
        LOG("rollForward");
        mCurrentIndex++;
        if(mCurrentIndex > mImagesCnt - 1){
            mCurrentIndex = mImagesCnt - 1;
        }
        setCurrentPaths();
    }

    //index向后移动一位
    @Override
    public void rollBackward() {
        LOG("rollBackward");
        mCurrentIndex--;
        if(mCurrentIndex < 0){
            mCurrentIndex = 0;
        }
        setCurrentPaths();
    }

    @Override
    public Bitmap[] getBitmap() {
        if(mCurren