Gridview每次滚动时都会刷新其内容

Question

我正在构建一个自定义gridview并使用picasso进行图像下载。我听说毕加索会自动缓存。但是当我滚动时，图像会被刷新。我想我犯了一个错误。请检查我的代码并帮助我找到错误。我已在下面发布了我的代码。

public class MoviesGridAdapter extends BaseAdapter{

   private Context context;
   private ArrayList<Movie> movies;
   private LayoutInflater inflater;
   private View gridView;
   private final String BASE_IMAGE_URL = ""; // unable to expose the link
   private Picasso mPicasso;


   public MoviesGridAdapter(Context context,ArrayList<Movie> movies) {
      this.context = context;
      this.movies = movies;
      mPicasso = Picasso.with(context);
      mPicasso.setIndicatorsEnabled(true);
   }

  @Override
  public int getCount() {
      return movies.size();
  }

  @Override
  public Object getItem(int position) {
      return null;
  }

  @Override
  public long getItemId(int position) {
      return 0;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
      gridView = convertView;
      ViewHolder holder;
      // when the view got recycled
      if(gridView == null){
          inflater = (LayoutInflater)        context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
          gridView = new View(context);
          holder = new ViewHolder();
          gridView = inflater.inflate(R.layout.grid_inner_layout,null);
          holder.movieView = (ImageView)   gridView.findViewById(R.id.imageView);
          gridView.setTag(holder);
      } else {
          // if the view still available
          gridView = convertView;
          holder = (ViewHolder) gridView.getTag();
      }

      // loading the image with picasso image loader
      mPicasso.
            .load(BASE_IMAGE_URL + movies.get(position).getPosterUrl())
            .resize(500, 750)
            .error(R.mipmap.ic_launcher)
            .into(holder.movieView);
      return gridView;
  }
  static class ViewHolder{
      ImageView movieView;
  }
}

gridview xml     

<GridView
    android:id="@+id/moviesGridView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:numColumns="auto_fit"
    android:columnWidth="150dp"
    android:verticalSpacing="2dp"
    android:horizontalSpacing="2dp"
    android:stretchMode="columnWidth"
    android:gravity="center"
     />

gridview项目布局xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="250dp"
        android:id="@+id/imageView"
        android:background="@android:drawable/screen_background_dark_transparent"/>
</LinearLayout>

谢谢！