As Xamarin Forms Developers even though we are developing most of our code in Forms, we still need to be attentive to each native platform features and how their ecosystem evolves and how does this affect our apps, a common case is using Shared Preferences each platform deals with them differently and that brings me to this new article.
Each platform decides how it handles it’s OS, and I want to focus on Shared Preferences and how it is affected by an awesome feature android has added to automatically backup user’s data that target Android 6.0(API Level 23) or later. Android saves app data by uploading it to the user’s Google Drive. But the issue is that this default behavior might not be made for every app scenario, you must be aware that if you have settings for enabling things like auto-login, themes preferences, and upgrades there might be some additional setup you need to make, so your app works correctly taking this into consideration.
If we don’t each time the user completely uninstall the app and installs it again android will restore its app data backup and cause unexpected behavior in your app fresh install flow, like an auto logging flow being triggered, or setting a theme by default he had before he uninstalled the app generating an inconsistent and erroneous logic for your app.
A few basics to know . . .
- Auto backup has a limit of 25MB per user (this has no charge for the user to store it’s app data).
- We can opt out of this feature completely.
- We can customize this feature to our needs.
- By default auto backup will include files in most of the directories that are assigned to your app by the Android system:
- Shared Preferences Files
- Files saved to your app’s internal storage, which you can access by
getFilesDir()orgetDir(String, int) - Files in the directory returned by
getDatabasePath(String)
Examples Cases
I will walk through 3 example app scenarios that could go wrong and sometimes unnoticed without proper testing of your app while developing (because let’s face it, sometimes edge cases like fresh install situations can fly by if we are continuously developing an app and don’t have the need to uninstall it completely from the device we are testing in).
Theming
Custom Authentication Experiences
How can we manage Android Auto Back feature
Once we know this default feature our Forms App will have in Android we can mitigate it accordingly, and Android provides us 2 ways to do it, we can either opt out completely of the auto back up feature or we can manage our app data more atomic and include or exclude what we don’t wish to persist in our backup.
Opting out of Feature
We can disable backups by simply setting the android:allowBackup property to false in our application tag in our Android Project manifest file.
Include and Exclude data
We must remember that Android is backing up by default almost all app related data, so how can we decide what to include or exclude? we simply need to define XML rules which will give us control on what we want to backup.
First, we create a new XML resource called back_up_rules.xml or any name you want to give it and define inside this file our rules using the <include> and <exclude> tags like for example:
Once we have our rules ready all that is left is to tell our Android Application where it can find the rules it should follow if the auto backup is enabled, we can do this by simply adding the android:fullBackUpContent attribute to the application tag in our application tag in the manifest file for our app:
Ce finito Guys! Now you are able to manage your app’s data backup correctly and solve the issue of why the shared preferences of your Forms App were always being persisted even after uninstall on Android.
Made with ❤ by Pujolsluis
Good References to learn more about Android Auto Backup feature
Back up user data with Auto Backup – Android:
https://developer.android.com/guide/topics/data/autobackup
Files that are backed up with the auto backup feature – Android:
https://developer.android.com/guide/topics/data/autobackup#Files
Credits for artwork components:
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