多个图像存储和表视图处理

Question

Despite there are a lot of themes around this topic, I seem very frustrated in the following situation :(

The app downloads and parses a JSON with about 1000 objects, which have in their attributes link for a small image. I need to download (once) these images, store them and use in my TableView as icons.

What is the best way to store such amount of files and to work efficiently with them while displaying the TableView?

Answer 1

I will tell you how will I do it but before I would like to give you a warning about downloading files from the Internet and storing them in your app.

I got one of my apps rejected from Apple lately because I violated rule 2.23 from the App Store Review Guidelines which says:

2.23 Apps must follow the iOS Data Storage Guidelines or they will be rejected

Since Apple is using iCloud lately you should minimize the traffic that each app will upload and therefore you should not have more than 40MB stored in your Documents folder of your app. They also say (if you read the links I provided):

Data that can be downloaded again or regenerated should be stored in the /Library/Caches directory.

And since the cache folder can be deleted by the iOS if needed, you should design your app to be prepared to download the images again in case they are gone, so keep this in mind.

Now for my solution, I think downloading 1000 files is too much (even if they are small files). I suggest that you have the files saved in a ZIP file on the server from which you are willing to download and unzip them on your disc once downloaded. This will be much easier and more practical. You can look here to see how to zip and unzip in your app.

After you have your files unzipped I suggest to have a small database (SQLite) from which you can load load the file names, store these names in an array, and then use this array to fill the images in your table in the function cellForRowAtIndexPath .

I hope this helps you. By the way, it is my way to do it but I am not saying it is the "best way" as you are asking :)

Answer 2

Given that you would like to keep these images/data persistent, you now have two options: You can manage them yourself or you can utilize Core Data to help you do it. I recommend Core Data.

If your not familiar with Core Data, you can start reading about it Here . It's a little bit daunting to get started, but once you've run through a tutorial it's extremely straightforward and will make your life much easier.

If you would like store the images yourself, or would like a more efficient Core Data structure, I recommend writing all of your images into your Documents directory as see Here . Then you can just store File path strings in your CD structure or manually in your plist like This .

And finally, for loading them into your TableView you can use those stored image paths to load UIImages with:

[[UIImage alloc] initWithContentsOfFile:filePath];

This would be placed within your:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

function so that you can set the image where you would like.