思路：將UIImage轉換成NSData，然後插入到NSMutableDictionary中。讀取時，用NSData讀出來，然後再轉換成UIImage

－存儲

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

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

iOS NSMutableDictionary中UIImage的存儲和讀取