inject SharedPreferences

[connyduck]

(this one is for @charlag)

Calling PreferenceManager.getDefaultSharedPreferences() will read the preference file from disk every time. This PR makes SharedPreferences a singleton so they will only be created once at appstart (with a few exceptions where it is hard to inject, e.g. in the openLink helper) which should help getting our ANRs down.

StrictMode policy violation; ~duration=285 ms: android.os.strictmode.DiskReadViolation
    at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1666)
    at libcore.io.BlockGuardOs.access(BlockGuardOs.java:74)
    at libcore.io.ForwardingOs.access(ForwardingOs.java:128)
    at android.app.ActivityThread$AndroidOs.access(ActivityThread.java:8054)
    at java.io.UnixFileSystem.checkAccess(UnixFileSystem.java:313)
    at java.io.File.exists(File.java:813)
    at android.app.ContextImpl.ensurePrivateDirExists(ContextImpl.java:790)
    at android.app.ContextImpl.ensurePrivateDirExists(ContextImpl.java:781)
    at android.app.ContextImpl.getPreferencesDir(ContextImpl.java:737)
    at android.app.ContextImpl.getSharedPreferencesPath(ContextImpl.java:962)
    at android.app.ContextImpl.getSharedPreferences(ContextImpl.java:583)
    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:221)
    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:221)
    at androidx.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:119)
    at com.keylesspalace.tusky.BaseActivity.onCreate(BaseActivity.java:96)
   ...

[connyduck]

Not sure why the SharedPreferences were created differently than everywhere else here?

[connyduck]

Too hacky?

[cbeyls]

While I agree that it's better to inject preferences everywhere for consistency and to make testing easier, it's not true that a new instance gets created every time.

The system keeps a static cache of SharedPreferences by name, and that cache includes the default SharedPreferences as well.
So it's not necessary to declare it as @Singleton in the dagger module because it's already a singleton.

[cbeyls]

Consider using a Dagger EntryPoint instead.

[connyduck]

oh that is nice, will do

[cbeyls]

This separate SharedPreferences instance was used to store temporary data that should ideally be stored to saveInstanceState instead of polluting the global SharedPreferences.

[connyduck]

🧐

[connyduck]

it's not true that a new instance gets created every time.

Maybe it is not a new instance, but according to StrictMode it does the disk read every time and that is my main concern here

[cbeyls]

Maybe it is not a new instance, but according to StrictMode it does the disk read every time and that is my main concern here

I was surprised because I didn't notice that behavior in my apps before. It turns out that the cache is Context-related so the file is read once per Context. If we make sure to pass the Application Context for every retrieval like we do now, the file will only be read once and the SharedPreferences don't need to be declared as Singleton in the Dagger module.