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🔮 Simplifies sharing fields and communication between Android components with custom scopes that are lifecycle aware.
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Chamber

License API API API Android Weekly API

Simplifies sharing fields and communication between
Android components with custom scopes that are lifecycle aware.

Android components are the essential building blocks of an Android application.
These independent components are loosely coupled. The benefit is that they are really independently reusable,
but it makes to hard communicate with each other.

The goal of this library is making easier to communicate and flow data with each other
component like Activity, Fragment, Services, etc.
And using custom scopes that are lifecycle aware makes
developers can designate scoped data holder on their taste.

When is useful?

When we need to hold some immutable data and it needs to be synchronized as the same data at each other components. For example, there is Activity A, Activity B, Activity C. And we need to use the same data in all Activity A~C that can be changed. Then we should pass a parcelable data A to B and B to C and getting the changed data reversely through onActivityResult.

Then how about the communication with fragments? We can solve it by implementing an interface, singleton pattern, observer pattern or etc, but the data flow would be quite complicated. Chamber helps to simplify those communications between Chamber scope owners.

chamber01

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Gradle

Add a dependency code to your module's build.gradle file.

dependencies {
    implementation "com.github.skydoves:chamber:1.0.1"
}

Usage

Chamber is scoped data holder with custom scopes that are lifecycle aware.

ChamberScope

The basic usage is creating a customized scope annotation using a @ChamberScope annotation.
@ChamberScope is used to build custom scopes that are lifecycle aware. Each scope is a temporal data holder that has ChamberField data and lifecycle stack. It should be annotated a class (activity, fragment, repository or any classes) that has ChamberField fields.

@ChamberScope
@Retention(AnnotationRetention.RUNTIME)
annotation class UserScope

ChamberField

ChamberField is an interactive class to the internal Chamber data holder and a lifecycleObserver
that can be observable. It should be used with @ShareProperty annotation that has a key name. If we want to use the same synchronized value on the same custom scope and different classes, we should use the same key.

@ShareProperty("name") // name is a key name.
var username = ChamberField("skydoves") // ChamberField can be initialized with any object.

setValue

Using the setValue method, we can change the ChamberField's value.

username.setValue("user name is changed")

postValue

Posts a task to a main thread to set the given value. So if you have a following code executed in the main thread:

username.postValue("a")
username.setValue("b")

The value b would be set at first and later the main thread would override it with the value a.

observe

We can observe the value is changed using the observe method.

username.observe { 
  log("data is changed to $it")
}

ShareLifecycle

Chamber synchronizes the ChamberField that has the same scope and same key.
Also pushes a lifecycleOwner to the Chamber's lifecycle stack.
Here is an example that has MainActivity and SecondActivity.

MainActivity

Chamber will create a @UserScope data holder.
when Chamber.shareLifecycle method called, the name field that has nickname key will be managed by Chamber and Chamber will observe the MainActivity's lifecycle state.

@UserScope // custom scope
class MainActivity : AppCompatActivity() {

  @ShareProperty("nickname")
  private var name = ChamberField("skydoves")

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    Chamber.shareLifecycle(scopeOwner = this, lifecycleOwner = this)

    name.value = "name value is changed"

    startActivity(SecondActivity::class.java)
  }
}

MainActivity -> SecondActivity

MainActivity starts SecondActivity using startActivity.
Chamber will observe the SecondActivity's lifecycle state. And the name field's value on the
SecondActivity will be updated by Chamber when shareLifecycle method called.

@UserScope
class SecondActivity : AppCompatActivity() {

  @ShareProperty("nickname")
  private var name = ChamberField("skydoves")

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_second)

    Chamber.shareLifecycle(scopeOwner = this, lifecycleOwner = this)

    // the value is "name value is changed". because it was set in MainActivity.
    log("name value is .. ${username.value}")

    name.value = "changed in SecondActivity"

    finish()
  }
}

The process of exiting scope

chamber02

SeondActivity -> MainActivity

finish method called in SecondActivity and we come back to the MainActivity.
when SecondActivity's lifecycle state is onDestroy, Chamber will not interact anymore with the SecondActivity's ChamberField and not observe lifecycle state.
And when MainActivity's lifecycle state is onResume, Chamber will update the ChamberField's value in MainActivity.

@UserScope
class MainActivity : AppCompatActivity() {

  @ShareProperty("nickname")
  private var name = ChamberField("skydoves")

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_second)
    
    // the value is "changed in SecondActivity". because it was set in SecondActivity.
    name.observe {
      log("name value is .. ${username.value}")
    }
  }
}

finish MainActivity

After all lifecycle owners are destroyed (all lifecycleOwners are popped from the Chamber's lifecycle stack), the custom scope data space will be cleared in the internal data holder.

Using on repository pattern

Architecturally, UI components should do work relate to UI works.
So it is more preferred to implement Chamber scope class on repository class.

@UserScope // custom scope
class MainActivityRepository(lifecycleOwner: LifecycleOwner) {

  @ShareProperty("nickname")
  var name = ChamberField("skydoves")

  init {
    // inject field data and add a lifecycleOwner to the UserScope scope stack.
    Chamber.shareLifecycle(scopeOwner = this, lifecycleOwner = lifecycleOwner)
  }
}

class MainActivity : AppCompatActivity() {

  private val repository = MainActivityRepository(this)

  // ...
}

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Design License

I designed flowcharts using UXFlow, it is following Attribution 4.0 International (CC BY 4.0).

License

Copyright 2019 skydoves (Jaewoong Eum)

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.
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