Kotlin Jetpack

A collection of useful extension methods for Android

• Arguments Bindings
• Preferences Bindings
• Resources Bindings

Arguments Bindings

public class ArgumentsFragment : Fragment() {
  public companion object {
    public fun newInstance(): ArgumentsFragment = ArgumentsFragment().apply {
      arguments = Bundle().apply {
        putBoolean("extra_boolean", true)
      }
    }
  }
  
  // Required binding without default value
  val booleanOrThrow by bindArgument<Boolean>("extra_boolean")

  // Required binding with default value
  val booleanOrDefault by bindArgument<Boolean>("extra_boolean", false)

  // Optional binding
  val booleanOrNull by bindOptionalArgument<Boolean>("extra_boolean")
}

These methods can be used with Activity, Fragment, and support library Fragment subclasses. You can also implement ArgumentsAware interface to provide a custom arguments source. Full list of supported bindings:

• bindArgument<Boolean> / bindOptionalArgument<Boolean>
• bindArgument<Double> / bindOptionalArgument<Double>
• bindArgument<Int> / bindOptionalArgument<Int>
• bindArgument<Long> / bindOptionalArgument<Long>
• bindArgument<String> / bindOptionalArgument<String>
• bindArgument<CharSequence> / bindOptionalArgument<CharSequence>
• bindArgument<Float> / bindOptionalArgument<Float>
• bindArgument<Enum> / bindOptionalArgument<Enum>
• bindArgument<Parcelable> / bindOptionalArgument<Parcelable>
• bindArgument<Serializable> / bindOptionalArgument<Serializable>

Every bindXXXArgument returns a ReadWriteProperty so they can be used with var's as well. In this case you don't have to deal with Bundle at all. No explicit Bundle creation, no silly EXTRA_XXX constants, no annoying Bundle.putXXX and Bundle.getXXX calls. Everything just works:

public class UserProfileFragment : Fragment() {
  public companion object {
    public fun newInstance(): UserProfileFragment = UserProfileFragment().apply {
      this.firstName = "Vladimir"
      this.lastName = "Mironov"
    }
  }
  
  // extra name is automatically inferred from property name ("firstName" in this case)
  var firstName by bindArgument<String>()

  // you can also provide a default value using "default" named argument
  var lastName by bindArgument<String>(default = "")
}

Gradle dependency:

compile "com.github.vmironov.jetpack:jetpack-bindings-arguments:0.14.2"

Preferences Bindings

public class PreferencesFragment : Fragment() {
  // Boolean preference
  var boolean by bindPreference<Boolean>("boolean", false)

  // Float preference
  var float by bindPreference<Float>("float", 0.0f)

  // Integer preference
  var integer by bindPreference<Int>("integer", 1)

  // Long preference
  var long by bindPreference<Long>("long", 1L)

  // String preference
  var string by bindPreference<String>("string", "default")
}

These methods can be used with Context, Fragment, support library Fragment, View, and ViewHolder subclasses. The example above uses a default SharedPreferences instance. You can always provide a custom one by implementing PreferencesAware interface:

public class PreferencesFragment : Fragment() {
  val preferences = PreferencesAware {
    activity.getSharedPreferences("CustomSharedPreferences", Context.MODE_PRIVATE)
  }
  
  var boolean by preferences.bindPreference<Boolean>("boolean", false)
  var float by preferences.bindPreference<Float>("float", 0.0f)
  var integer by preferences.bindPreference<Int>("integer", 1)
  var long by preferences.bindPreference<Long>("long", 1L)
  var string by preferences.bindPreference<String>("string", "default")
  
  // Optional preferences are supported as well
  var optionalLong by preferences.bindOptionalPreference<Long>()
  var optionalString by preferences.bindOptionalPreference<String>()
}

Although only Boolean, Float, Int, Long and String preferences are supported by default, the library can be easily extented to support custom type of preference. Adapter interface can be implemented in order to convert any type to a supported one. Here is an example how to imlement json-based preferences using Gson:

public inline fun <reified E : Any> Any.bindGsonPreference(default: E, key: String? = null): ReadWriteProperty<Any, E> {
  return bindPreference(default, GsonPreferenceAdapter(E::class.java), key)
}

public inline fun <reified E : Any> Any.bindGsonPreference(noinline default: () -> E, key: String? = null): ReadWriteProperty<Any, E> {
  return bindPreference(default, GsonPreferenceAdapter(E::class.java), key)
}

public class GsonPreferenceAdapter<T>(val clazz: Class<T>, val gson: Gson = GsonPreferenceAdapter.GSON) : Adapter<T, String> {
  override fun type(): Class<String> = String::class.java
  override fun fromPreference(preference: String): T = gson.fromJson(preference, clazz)
  override fun toPreference(value: T): String = gson.toJson(value)

  public companion object {
    public val GSON = Gson()
  }
}

Usage:

public data class Profile(val firstName: String? = null, val lastName: String? = null)

public class ProfileManager(val context: Context) {
  public var profile by bindGsonPreference(Profile())
}

Gradle dependency:

compile "com.github.vmironov.jetpack:jetpack-bindings-preferences:0.14.2"

Resources Bindings

public class ResourcesFragment : Fragment() {
  // Boolean resource binding
  val boolean by bindResource<Boolean>(R.boolean.boolean_resource)

  // Color resource binding
  val color by bindResource<Int>(R.color.color_resource)

  // Drawable resource binding #1
  val bitmap by bindResource<BitmapDrawable>(R.drawable.drawable_bitmap)
  
  // Drawable resource binding #2
  val vector by bindResource<VectorDrawable>(R.drawable.drawable_vector)

  // Dimension resource binding
  val dimension by bindResource<Int>(R.dimen.dimen_resource)

  // String resource binding
  val string by bindResource<String>(R.string.string_resource)
}

These methods can be used with Activity, Context, Fragment, support library Fragment, View, and ViewHolder subclasses. You can also implement ResourcesAware interface to provide a custom resources source. Full list of supported bindings:

• bindResource<Boolean>(R.boolean.boolean_resource)
• bindResource<Int>(R.integer.integer_resource)
• bindResource<Int>(R.color.color_resource)
• bindResource<ColorStateList>(R.color.color_resource)
• bindResource<Drawable>(R.drawable.drawable_resource)
• bindResource<Int>(R.dimen.dimen_resource)
• bindResource<Float>(R.dimen.dimen_resource)
• bindResource<String>(R.string.string_resource)
• bindResource<CharSequence>(R.string.string_resource)
• bindResource<IntArray>(R.array.array_resource)
• bindResource<Array<String>>(R.array.array_resource)
• bindResource<Array<CharSequence>>(R.array.array_resource)

Gradle dependency:

compile "com.github.vmironov.jetpack:jetpack-bindings-resources:0.14.2"

License

Copyright 2015 Vladimir Mironov

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.