We are wanting to implement an offline mode for our react-native application. We will be working with quite large amount of data (aprox. 40-50mb). It is an array of aprox. 16000 objects.
As far as I know, there are two ways to save this data.
Using AsyncStorage - android has a limit of 6mb, but I've read somewhere, that it can be increased.
Using json file - Downloading that data as json file using react-native-background-downloader and then using react-native-fs to save it and load it if the user has no connection to internet.
Personally I think that the second option is better, even though it requires permission to file storage.
Am I missing any other factors to consider? Are there any other options for offline access?
In the end opted out for usage of the json file as there is limit on android. On load of the application I take these data and load them into variable in mobX store. Which functions same as any variable.
I was afraid that mobile phones will have problem sorting across the 16000 objects in array, but there have been no reports of this thing going wrong so far. (In production for 4-5 months right now)
So basically when you hit "enable offline mode" I ask for the file storage permission and download the file using react-native-fs.
Then on the next startup of the application I just read the data off the JSON file.
Related
For our app we need the app the work offline 100% with the most recent data.
Normally the app uses a symfony api platform API to fetch data paginated server side.
But when someone is using the app in a area without Internet he still need to be able to access all data to make a new job and que it for when he is online.
So our tough is to make a json that has all the data and send it to the phone when the phone has connection.
When the phone is using the app live, it will use pagination from server and fetch data.
And when offline it will use the local downloaded data file.
Problem is the data is large, so storing it is the problem.
We are now using redux persist and we see so many people have problems with crashes and mobile ram.
We also thought of using sqlite or just async to store a json file, or download a sqlite file from the app.
How do you guys feel about this
You can use react-native-local-mongodb. This can help you store a json database on your phone.
Other option is to have react-native-sqlite-storage in case your database has to be relational and requires table.
You will have to sync this local copy with the server once this user is online. This too can be done if you have the timestamp saved of the last sync. So after that, you ll just have to sync the data created after that timestamp.
However, I had also implemented react redux persist and it didnt crash. I suppose, the reason for crash must me something else.
Over many different Objective-C iOS coding projects I have frequently come across the issue of having data be accessible after I initially got it.
For example, currently I am reading from the stackoverflow API. I do this with a session and get a dictionary back (my JSON response).
But outside the scope of the session, the dictionary is unavailable! I can't copy the contents to a different dictionary that I've defined globally, or anything. It's like it disappears outside of the session.
So I am wondering, what's the best way to save this data that I want to use? From what I've been reading it seems like NSUserDefaults or maybe creating a plist file, although admittedly I've been having trouble with both options. If there is a method that is best for this then I can concentrate on that.
Thank you!
It depends on how persistent you want to be.
If you save this dictionary into a global variable, it is stored in the part of device's RAM that is reserved for the running app. When the app stops running (gets killed by OS or removed by the user) or if your device reboots - this memory is lost.
If you save this dictionary onto the device's flash memory drive (and its file system) - it will live past restarts/reboots.
Usually people combine the approaches: when you get the data from the network, you keep it in a global variable, and save it to the file system. After the app restart you try to load the data from the file system. The reason for not using the FS all the time is that it is much slower than RAM access. I guess I'm describing caching.
Note that you can implement manual caching (using plain data or text files, NSUserDefaults, Core Data or other libraries), but also you can utilize a builtin HTTP cache - NSURLCache. If you create a session with NSURLSession.sharedSession it will use the default NSURLCache and respect a caching policy dictated by the server side.
For more control and full offline support I'd recommend to implement caching manually. See this about reading and writing plists and writeToFile:atomically:.
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'm a little bit confused over the various types of storage that is available to Windows Store Apps.
Let's say I had a notepad app, where users can view, create, and edit notes. What storage type would I use for storing the notes? Local storage? Write the notes out to files in the user's Documents folder? Also, what if I wanted to sync a user's notes via the cloud? I understand that Roaming Data has a rather low size limit.
Almost all the options you mention are possible for a notepad application. Except the roaming data option, that only allows you to store 100KB of data.
I will try to sum up the options that you have and add a few more:
Localstorage
You can easily add these files to localstorage, you can store it in file format or serialize your object and store that one. Very easy to implement. Con is that only your app can access these files.
Documents folder
Also an option. Made easy by use of different filepickers. For example the FileOpenPicker or the FileSavePicker. Files can be stored in the format you like and can be accessed by other apps or through the file explorer.
Roaming data
No option for files due too the limited space
Skydrive API
If you want to store files in the Cloud and access them anywhere you could consider the skydrive api. Also note that if you use the filepickers you also have the option to save/load these files to skydrive. (Although in that case the user chooses where to store the file.)
Windows Azure Mobile Services
Another option if you want to store data in the cloud. Gives you the ability to store your data in a table/tables. Very easy to implement. More info about mobile services can be found here
SQL Lite
If you need a local database to store your data than SQLLite can be an option. Tim Heuer has wrote a nice blogpost about how to use SQLLite in your windows 8 app. You can find it here
Hopefully this clears up things a bit and gives you some ideas about what to choose for your app?
In an app like this (a notepad style app), the logical place to store you files in in the user's documents folder. That way they are accessible to the user from other apps as well as the current one. There is, of course, the option to roll your own methods to upload the data to SkyDrive as well, but you really shouldn't rely on this as being your only data source - what if the user is offline?
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.