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PrefExtensions

Declarative extensions on SharedPreferences and Editor with the help of annotation processing.

This project is being continued at PreferenceX

Use Case

Often times, SharedPreference getters and setters are non declarative and not the most readable. Typically, to get a value from SharedPreference, you do a variation of:

val sharedPreferences = context.getSharedPreferences("file_name", Context.MODE_PRIVATE)
val appStartCount = sharedPreferences.getLong("appStartCount", 0)

To insert a value, you do:

val editor = sharedPreferences.edit()
editor.putLong("appStartCount", 1)

This isn't the most readable API. Without reading the key, it's hard to know what we're going for.

Usage

PrefExtensions creates a readable API by generating extensions on SharedPreferences and SharedPreferences.Editor. The same example would be something like:

Declare your preference variable:

class MyPreferences {
  @Preference private val appStartCount: Long? = null
}

Get that value

// Or get from your favorite DI
val sharedPreferences = context.getSharedPreferences("file_name", Context.MODE_PRIVATE) 
val appStartCount = sharedPreferences.getAppStartCount() // Generated extension

Set the value

val editor = sharedPreferences.edit() // Or get from your favorite DI
editor.putAppStartCount(2) // Generated extension

Default Values

SharedPreference reads require a default value to be given. You can easily define the default value for your given preference with an optional parameter:

@Preference(defaultLong = 1L) 
private val appStartCount: Long? = null

@Preference(defaultString = "hello world")
private val greetingText: String? = null

PrefExtensions also takes advantage of Kotlin's default values in parameters and the generated code creates an optional parameter in the getter. This is useful for one off-ing a different defaultValue than the one you provided in the annotation.

Generated Code

fun SharedPreferences.getAppStartCount(defaultValue: Long = 1): Long = getLong("appStartCount", defaultValue)

Usage

preferences.getAppStartCount(defaultValue = 20)

Custom Keys

PrefExtensions can be added incrementally into your project. If you already have a SharedPreference entry defined with a particular key that is not very reader friendly (like "app_launch_count"), you can easily define a custom key to your Preference declaration.

Using this, you can continue to use the newer API in some cases, while still supporting access through the usual SharedPreference API.

@Preference(key = "app_launch_count") 
private val appStartCount: Long? = null

License

Copyright 2018 Shaishav Gandhi.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.