I'm building an application that needs to download web content for offline viewing on an iPad. At present I'm loading some web content from the web for test purposes and displaying this with a UIWebView. Implementing that was simple enough. Now I need to make some modifications to support offline content. Eventually that offline content would be downloaded in user selectable bundles.
As I see it I have a number of options but I may have missed some:
Pack content in a ZIP (or other archive) file and unpack the content when it is downloaded to the iPad.
Put the content in a SQLite database. This seems to require some 3rd party libs like FMDB.
Use Core Data. From what I understand this supports a number of storage formats including SQLite.
Use the filesystem and download each required file individually. OK, not really a bundle but maybe this is the best option?
Considerations/Questions:
What are the storage limitations and performance limitations for each of these methods? And is there an overall storage limit per iPad app?
If I'm going to have the user navigate through the downloaded content, what option is easier to code up?
It would seem like spinning up a local web server would be one of the most efficient ways to handle the runtime aspects of displaying the content. Are there any open source examples of this which load from a bundle like options 1-3?
The other side of this is the content creation and it seems like zipping up the content (option 1) is the simplest from this angle. The other options would appear to require creation of tools to support the content creator.
If you have the control over the content, I'd recommend a mix of both the first and the third option. If the content is created by you (like levels, etc) then simply store it on the server, download a zip and store it locally. Use CoreData to store an Index about the things you've downloaded, like the path of the folder it's stored in and it's name/origin/etc, but not the raw data. Databases are not thought to hold massive amounts of raw content, rather to hold structured data. And even if they can -- I'd not do so.
For your considerations:
Disk space is the only limit I know on the iPad. However, databases tend to get slower if they grow too large. If you barely scan though the data, use the file system directly -- may prove faster and cheaper.
The index in CoreData could store all relevant data. You will have very easy and very quick access. Opening a content will load it from the file system, which is quick, cheap and doesn't strain the index.
Why would you do so? Redirect your WebView to a file:// URL will have the same effect, won't it?
Should be answered by now.
If you don't have control then use the same as above but download each file separately, as suggested in option four. after unzipping both cases are basically the same.
Please get back if you have questions.
You could create a xml file for each bundle, containing the path to each file in the bundle, place it in a folder common to each bundle. When downloading, download and parse the xml first and download each ressource one by one. This will spare you the overhead of zipping and unzipping the content. Create a folder for each bundle locally and recreate the folder structure of the bundle there. This way the content will work online and offline without changes.
With a little effort, you could even keep track of file versions by including version numbers in the xml file for each ressource, so if your content has been partially updated only the files with changed version numbers have to be downloaded again.
Related
In the documentation sample code for how to deal with user uploaded files, they save it as a trusted filename for filestorage via GetRandomFileName, and a trusted filename for HTML display.
In the comments it says: "In most production scenarios, an anti-virus/anti-malware scanner API is used on the file before making the file available for download or for use by other systems."
Is that going to be before it is saved with a random filename or after? Because that is the point of saving it as a random filename, so that it doesn't get executed? And when the scanning is done, how is the file going to be made available? I guess the file just has to be renamed if it passes the scan or else deleted? If so, what is the proper way to get the original file extenstion? And do you know of any good scanners that are gratis that are popular to use?
I try to learn web development. Thanks for your time and help.
The renaming of the file here has nothing to do with the anti-virus protection. The files don't tend to execute themselves whatever their name is. Same with the virus scan: it's not for the server protection, it's for the users protection. If your server executes the binary it gets from the client, it's a security breach regardless of whether it's a virus or not.
The renaming here is probably done just to be able to store the duplicates. That being said, in the production scenarios you'll probably never store the incoming files as physical files on the FS. They usually go to the DB as blobs, so the name is not an issue.
This is just a sample app designed to teach how to work with binary streams and file controllers. Don't expect too much from it in terms of applicability to the real solutions.
I have an iOS 7 app, that is using Core Data. Some of the Core Data objects has a related (one to one relationship) images that are > 1MB & < 4MB and are stored in the app’s Document folder. Core Data objects only stores image names as string.
I want to integrate iCloud support for the app so I can sync data between devices. I am planning to use iCloud Core Data storage to sync Core Data objects. But what to do with the images?! After reading different posts, I found a couple of options that are highlighted underneath. I am struggling to pick one, that would suit me best. It would be nice to know someones experience/recommendations. What I should be careful with, or what didn't I think of? I also need to consider migration of the existing data to the option I will pick.
OPTION 1. Store UIImage in the Core Data as Binary Data with External Binary Data option (read here). At this moment is seems to be the easiest solution, but I guess not the best. From Documentation:
It is better, however, if you are able to store BLOBs as resources on
the filesystem, and to maintain links (such as URLs or paths) to those
resources.
Also will the external files be synced? If so, how reliable the sync would be if the user quits on minimises the app, will the sync process resume? From objc.io about External File References:
In our testing, when this occurs, iCloud does not always know how to
resolve the relationship and can throw exceptions. If you plan to use
iCloud syncing, consider unchecking this box in your iCloud entities
OPTION 2. Store images using UIDocument (good tutorial here) and somehow track relation between Core Data entry and UIDocument. From what I understand whatever I put in this directory will be automatically synchronised to the iCloud by a system daemon. So if the user quits the app, the images will still be synced to the iCloud, right?
OPTION 3. Using FileManager(more info here). I haven’t read a lot about this approach, but I think it can also work.
OPTION 4. Any other?
There are similar posts (e.g. Core Data with iCloud design), but unfortunately they don't fully answer my question.
Seems Apple will reject application because of large database iCloud synchronization.
I think the best solution is to store images on a remote host, and keep Image URL in CoreData.
And also Local path of image should be resolvable from remote URL.
So the algorithm will look like this ->
1) Getting Remote URL from CoreData.
2) Resolve local path of image.
3) If local image exists retrieve it, otherwise read it from remote and save it to local storage.
You can have a look to Amazon S3 server here.
I am developing a Win8 Store app which allows users to download different types of files from an online learning platform and store them locally. I am also considering the function to help users organize these downloaded files by placing them in different folders (based on course name and etc.).
I was using Documents Library previously. But for every type of file that the user could download, I need to add a file type association, which does not make a lot of sense since my app would be able to open such files. So which local storage should my app use?
Many thanks in advance.
Kaizhi
The access to storage by Windows Store apps is quite restrictive, especially the DocumentsLibrary.
As you have noticed, you need to declare a file type association for every file type you want to read from or write to the DocumentsLibrary. This means your app need to handle file activations for these types in a meaningful way, which your app probably should not do.
But even if you jump through this hoop, there is another one that is not documented on the MSDN page of the DocumentsLibrary, but "hidden" in a lengthy page about app capability declarations: According to the current rules, you are not allowed to use the DocumentsLibrary for anything but offline access to SkyDrive! Bummer...
So what's left?
You can use SkyDrive or another cloud storage to put files in a well known place (which might or might not be somewhere on the hard disk). This is probably both overkill and undesirable in your case.
Or you save the files in the local app storage, provide your own in-app file browser and open the files with their default app. Seems viable to me.
Or, maybe, you can do something with share contracts or other contracts. I don't know much about these yet, but I doubt that they are helpful in your situation.
And that's it...
(Based on my current experience. No guaranty for correctness or completeness)
I'm currently developing an order entry application for my company. This means I need to download approximately 1900 product images to the iPad, and that's just the normal images. I also need to download an equal amount of thumbnails. The reason for downloading the images to the iPad instead of just displaying them from a given URL is that our reps wander into large stores which often don't have stable internet connections.
What would be the best course of action? The images are stored on our servers, but you need to be authenticated using Basic Auth before you can access those. I have thought of just downloading them one-by-one, which is tedious, or group them together on the server as a zip-file but that would be a large file.
A one-by-one is a valid options for the download. I have done projects with similar specs, so what I advise:
Use some 3rd party library to help you with the download of the images. MKNetworkKit for example. If you feel confortable enough, NSURLConnection is more than enough.
Store the images in the application sandbox.
Instead of downloading the thumbs, just create them on the go when you need them (Lazy pattern). Unless your image's thumbs are somewhat different than the original (some special effect).
I'm building a Mac OS X application that can be used to create 'projects'. When a user saves a project, they will be saving many resources: image files, text files, sqlite files etc.
I can either create a folder in Documents for each project, and within that folder I can place all the project assets, and just include a single project file that is used to open the project.
I've read about NSBundle which I'd like to use. But I've only read about them in the context of application bundles. Is it possible to use NSBundle in this way? Where the user only sees a single file, and can move it wherever they like.
Does it make sense to do what I'm trying, using NSBundle? Or is there another way to do this?
(I'm fairly new to MacOS X programming)
UPDATE
I believe iPhoto uses this method to store the "iPhoto Library", this is what I'd like to do with my application, is NSBundle what I should be looking into?
Yes, it is possible and was used in quite a few apps in the past. The method is described in this document. Once it's clearly declared in your app's Info.plist, Finder will show the resulting bundle as one file.
However, I can't recommend you to do that. Apple's own Keynote was using the bundle approach in the past, but it no longer uses it any more. Similarly, OmniGraffle (which is a diagramming app on OS X with a long history) used bundles to save projects, but it stopped doing that, too.
The reason is that the bundle is still seen as a directory by the non-Apple email software, or any browser, etc, although the Finder shows it as a file. It would be a mess if a user wants to attach your document in the bundle format to an email s/he is composing in Gmail inside a browser, say. That confused a lot of people.
So, it's possible, but I don't recommend it. One way out is to use the zipped bundle as the user-visible file, and to unzip it when the user opens it into a temporary directory. Then you can use NSBundle and/or NSFileWrapper apis to access files inside it.
Apple's File Wrapper sample seems to be what you want:
http://developer.apple.com/library/mac/#samplecode/PersistentDocumentFileWrappers/Introduction/Intro.html
It also demonstrates how to save a Core Data persistent store in the bundle. You can leave that part out if you just want to store resources.
The NSBundle class represents the application bundle, and can be used to access resources within the applicationm but you would you it for application data, not user data.
For each of the resources you mention, there's a way of saving this type, for example, for image files, you could use NSData to save the image data to disk, and for text files you could use the method writeToFile:atomically:encoding:error:.
You may very well want to take a look at Core Data (http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/CoreData/cdProgrammingGuide.html), a very good framework for managing the user's data model, to see if this would fit your needs.