思路：将UIImage转换成NSData，然后插入到NSMutableDictionary中。读取时，用NSData读出来，然后再转换成UIImage

－存储

UIImage *image = [self getPicture: id];NSData *imageData = UIImagePNGRepresentation(image);[tmpDic setObject:imageData forKey:@"imageData"];

－读取

NSData *imageData = [object objectForKey:@"imageData"];if (imageData) {    UIImage *image = [[UIImage alloc] initWithData:imageData];    imageView.image = image;}else{    //...}