Xamarin.Forms - Read SharedPreferences of old version apk

andreMetal 46

Hello, this is my situation: I have an Android application written in java using Android Studio already distributed in the store. Recently with my team we decide to rewrite the app using Xamarin.Forms. The old version app used SharedPreferences to store and read some settings. We tried to read the same setting with the new xamarin forms version without success. My first question is: is it possible to do what we are trying to? If yes, is there a good way to do?
Thanks in advance for the reply.

Alessandro Caliaro 4,181 Reputation points

2021-01-19T09:30:05.257+00:00

Hi.
So, if I have understand, you have an app A (Android) and an app B (Xamarin Forms). These apps have the same applicationID, so you have to "substitute" (update) A with B and you would like to read with B the A's preferences, correct? I think it's possible.. (if they have the same applicationID / packagename). Which is the error? Do you have empty preferences?
andreMetal 46 Reputation points

2021-01-19T09:35:53.217+00:00

Hello,
yes this is exactly my situation, same applicationID and packagename, but the result is that always return empty preferences. The Xamarin forms app will be the new version of the Android app.
Alessandro Caliaro 4,181 Reputation points

2021-01-19T10:43:19.287+00:00

What do you use in XF to get preferences? and in Android native? can you post a piece of code?
andreMetal 46 Reputation points

2021-01-19T11:04:16.897+00:00
This is the method used in the Android (java) version:
public static String Load(String key){
SharedPreferences sharedPreferences = context.getSharedPreferences("SETTINGS", context.MODE_PRIVATE);
String ret=sharedPreferences.getString(key, "");
return ret;
}

This is the Xamarinf forms method:

public string Load(string key) { ISharedPreferences sharedPreferences = Android.App.Application.Context.GetSharedPreferences("SETTINGS", FileCreationMode.Private); string result = sharedPreferences.GetString(key, "Not found"); return result; }
Alessandro Caliaro 4,181 Reputation points

2021-01-19T11:51:10.617+00:00

The XF code is written in Android Project, right?
If you debug the Android app and then the XF app, do you have only one icon on the display? (are you sure is not deployed a second app to the device?)
andreMetal 46 Reputation points

2021-01-19T12:01:13.577+00:00

Yes, the code is written in the Xamarin.Android project. If I start debugging the Xamarin application from Visual Studio and the old Android app is installed in the device, the old app is uninstalled and substitute with the new version.

Accepted answer

JarvanZhang 23,951 Reputation points

2021-01-20T09:22:15.48+00:00

Hello,

Welcome to our Microsoft Q&A platform!

Hi, AndreaTizzoni-0935. I created a basic sample to test the function in debug mode, the data which is saved in as cannot be get in Xamarin. It seems that it uninstall the java version and install xamarin version instead of overwriting the previous version.

update

This will work fine in release mode, installing the c# version application with the same keystore of the java app will make it.

Best Regards,

Jarvan Zhang

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Alessandro Caliaro 4,181 Reputation points

2021-01-20T09:41:47.517+00:00

@JarvanZhang have you tried in debug on in release mode signing the two apk with the same key?

James Montemagno 351 Reputation points Microsoft Employee

2021-01-20T23:16:29.627+00:00

This will work fine in release mode. Install the old version and then install the new version of release and should work fine. When you do debug builds and deploys the settings can get erased.

JarvanZhang 23,951 Reputation points

2021-01-21T01:31:17.007+00:00

I tested the function in debug mode.

andreMetal 46 Reputation points

2021-01-22T10:05:15.187+00:00

Thank you for the reply. I tested in Release mode, archiving a new apk using the same keystore of the old app, upgrading the Version Code and now I'm able to read the Preferences.

Nam Pham 116 Reputation points

2023-09-15T09:03:23.5766667+00:00

Hi @andreMetal , you mean you can get SharedPreferences in old Android app. Can you share the code?
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1 additional answer

Alessandro Caliaro 4,181 Reputation points

2021-01-19T12:06:29.1+00:00
https://stackoverflow.com/questions/26668509/how-do-i-use-sharedpreferences-in-xamarin-android

Take a look to this.
I see also a

mSharedPrefs = PreferenceManager.GetDefaultSharedPreferences(mContext);

that seems you are not using
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andreMetal 46 Reputation points

2021-01-19T15:32:47.02+00:00

Thank you for the reply but it doesn't work.

Alessandro Caliaro 4,181 Reputation points

2021-01-19T16:07:10.927+00:00

are you working in debug or in release mode?

andreMetal 46 Reputation points

2021-01-19T16:49:41.633+00:00

In Debug mode the preferences result is an empty string. If I create a signed apk I can't terminate the installation.

James Montemagno 351 Reputation points Microsoft Employee

2021-01-20T23:17:15.917+00:00

This will work fine in release mode. Install the old version and then install the new version of release and should work fine. When you do debug builds and deploys the settings can get erased. You can even use Essentials as it uses the same APIs -> https://learn.microsoft.com/en-us/xamarin/essentials/preferences
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Xamarin.Forms - Read SharedPreferences of old version apk

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