//保存图片
-(void)saveImageDocuments:(UIImage *)image{
  //拿到图片
  UIImage *imagesave = image;
  NSString *path_sandox = NSHomeDirectory();
  //设置一个图片的存储路径
  NSString *imagePath = [path_sandox stringByAppendingString:@"/Documents/test.png"];
  //把图片直接保存到指定的路径（同时应该把图片的路径imagePath存起来，下次就可以直接用来取）
  [UIImagePNGRepresentation(imagesave) writeToFile:imagePath atomically:YES];
}
// 读取并存贮到相册 
-(UIImage *)getDocumentImage{
  // 读取沙盒路径图片
  NSString *aPath3=[NSString stringWithFormat:@"%@/Documents/%@.png",NSHomeDirectory(),@"test"];
  // 拿到沙盒路径图片
  UIImage *imgFromUrl3=[[UIImage alloc]initWithContentsOfFile:aPath3];
  // 图片保存相册
  UIImageWriteToSavedPhotosAlbum(imgFromUrl3, self, nil, nil);
  return imgFromUrl3;
}