Question regarding core data and the camera

问题:

So I am working on an app that uses core data to store attributes of objects that the user can set. I have primarily been focusing on the first part, which was setting everything up on the core data side, and now I am ready to move on to the next part which deals with the camera. I want to be able to add a city, or other geographical location (this is the object) and then be able to take pictures within my application that would accordingly store these pictures (or attributes) under the object. When I click on New York on my uitableview for example, I'd be able to view any number of pics that I took in NY. When I click on Florida, I'd be able to view any pics I took in Florida. So, my question is about whether or not that is a possibility? Sorry, that was a vague question. If I were to take pictures from within my app, would I be able to save them there as well? And make a list of them in my app? I guess I am envisioning a seperate core data-esque looking uitableview withing the place object letting you manage pictures so that they are directly viewable in like a slide show mode where I'd be able to see all the pictures I took at that location. Is that a possibility or would they save in the default picture location in the pictures app? Would there conceivably be any memory restrictions? Or would I be able to pull from the media memory (8gb, 16gb, etc)? I guess my questions aren't for specific code examples as much as they are for directional purposes. If anyone has any insights/ideas to help me out it would be greatly appreciated. Thanks!

回答1:

The design you describe is definitely possible.

You can give users the opportunity to select a picture (and/or video) from their photo library and/or take a new one with the camera and then use/edit/store it in your application. Check out the UIImagePickerController and the UIImagePickerControllerDelegate protocol.

You can store images directly in Core Data as a transformable attribute by converting them to NSData using UIImagePNGRepresentation() or UIImageJPEGRepresentation(). If you do this, it is recommended that you create a separate entity with the image data attribute so that you can load your other attributes quickly (and only pull in the image data across the relationship as needed). Alternatively, you can store the images in files in your app's Documents directory and save the filename as an attribute in your entity.

Check out the TTThumbsViewController in the Three20 library for a nice way to show a grid of photo thumbnails.

回答2:

I would really recommend storing the files to the application Documents directory, and storing paths to them in the database. You can do it the other way but storing them in files keeps the database smaller and gives you more flexibility to upload them somewhere without having to load the whole image in memory.