android development in the skip pit --GridView use Glide Load picture does not show

Grideview with local display picture list, loaded with the Glide framework, specific call as follows:

Glide.with(mContext).load(Uri.fromFile(file)).into(imageView);

But the amazing thing happened, nothing is displayed, and no error! ! ! ! ! After the search for information online without thinking about either display a placeholder try, as follows

Glide.with(mContext).load(Uri.fromFile(file)).placeholder(R.drawable.add).into(imageView);

Then, the picture shows up, why?