Android - How to use SharedPreferences in non-Activity class?
SharedPreferences are related to context. You can only reference it through a context.
You can simply pass context as a parameter to your class. For example in the constructor.
In your activity do:
MyClass myClass = new MyClass(this);
The solution i found to this was:
1-In an MainActivity class (i.e always launched before getting any context in project) create a static variable for the context:
public static Context contextOfApplication;
2-In an important method of this class (Such as onCreate, the constructor, etc) initialize this variable using the getApplicationContext method:
public void onCreate() {
contextOfApplication = getApplicationContext();
}
3-In the same class Create a "getter" method for this variable (it must also be static):
public static Context getContextOfApplication(){
return contextOfApplication;
}
4-In the non-activity class get the context by calling the created method statically:
Context applicationContext = MyActivityClass.getContextOfApplication();
5-Use the PreferenceManager Class to get the SharedPreferences variable:
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(applicationContext);
Hope it helps.
In Kotlin, there's a nice & simple wrapper-based solution – just copy & paste the code into a new AppPreferences.kt
file and follow the 4 TODO steps outlined in the code:
import android.content.Context
import android.content.Context.MODE_PRIVATE
import android.content.SharedPreferences
import androidx.core.content.edit
object AppPreferences {
private var sharedPreferences: SharedPreferences? = null
// TODO step 1: call `AppPreferences.setup(applicationContext)` in your MainActivity's `onCreate` method
fun setup(context: Context) {
// TODO step 2: set your app name here
sharedPreferences = context.getSharedPreferences("<YOUR_APP_NAME>.sharedprefs", MODE_PRIVATE)
}
// TODO step 4: replace these example attributes with your stored values
var heightInCentimeters: Int?
get() = Key.HEIGHT.getInt()
set(value) = Key.HEIGHT.setInt(value)
var birthdayInMilliseconds: Long?
get() = Key.BIRTHDAY.getLong()
set(value) = Key.BIRTHDAY.setLong(value)
private enum class Key {
HEIGHT, BIRTHDAY; // TODO step 3: replace these cases with your stored values keys
fun getBoolean(): Boolean? = if (sharedPreferences!!.contains(name)) sharedPreferences!!.getBoolean(name, false) else null
fun getFloat(): Float? = if (sharedPreferences!!.contains(name)) sharedPreferences!!.getFloat(name, 0f) else null
fun getInt(): Int? = if (sharedPreferences!!.contains(name)) sharedPreferences!!.getInt(name, 0) else null
fun getLong(): Long? = if (sharedPreferences!!.contains(name)) sharedPreferences!!.getLong(name, 0) else null
fun getString(): String? = if (sharedPreferences!!.contains(name)) sharedPreferences!!.getString(name, "") else null
fun setBoolean(value: Boolean?) = value?.let { sharedPreferences!!.edit { putBoolean(name, value) } } ?: remove()
fun setFloat(value: Float?) = value?.let { sharedPreferences!!.edit { putFloat(name, value) } } ?: remove()
fun setInt(value: Int?) = value?.let { sharedPreferences!!.edit { putInt(name, value) } } ?: remove()
fun setLong(value: Long?) = value?.let { sharedPreferences!!.edit { putLong(name, value) } } ?: remove()
fun setString(value: String?) = value?.let { sharedPreferences!!.edit { putString(name, value) } } ?: remove()
fun remove() = sharedPreferences!!.edit { remove(name) }
}
}
Now from anywhere within your app you can get a value like this:
val heightInCentimeters: Int? = AppPreferences.heightInCentimeters
val heightOrDefault: Int = AppPreferences.heightInCentimeters ?: 170
Setting a value to the SharedPreferences
is just as easy:
AppPreferences.heightInCentimeters = 160 // sets a new value