AbstractMvp

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Language
Kotlin
Version
1.0.3 (Oct 26, 2018)
Created
Aug 28, 2018
Updated
Oct 26, 2018
Owner
Robert (RobertApikyan)
Contributor
Robert (RobertApikyan)
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MinSDK 14+

AbstractMvp

AbstractMvp is a library that provides abstract components for MVP architecture realization, with problems solutions that are exist in classic MVP.

CLASSIC MVP ISSUES THAT ARE SOLVED IN ABSTRACT MVP

Nullable View instance

In classic MVP realisation we attach the view instance to the presenter and detach it when view is going to be destroyed, so at some point the view instance inside presenter will be null and every time before accessing the view instance we need to make null check, in order to avoid NullPointerException. This behavior is secure, but it requires additional null check. To overcome with this, AbstractMvp library provides ViewActions, which are closures, that will be executed only when the view is not null. (later, detailed about ViewAction).

Lost UI updates

After performing some background jobs presenter needs to update ui, but at that point view instance is null. Since view is null, the UI updates will not be executed. AbstractMvp provides ViewActionDispatcher as a solution, which is another abstraction layer and it knows when the view is attached or not, and if it is not attached the viewAction will be cached inside ViewActionDispatcher, and executed when view become attached again.

Not Persistence Presenter

Usually presenter instance is inside our viewController (Activity or Fragment), and it will be destroyed with viewController. To overcome this, and make presenter instance persistence per viewController life scope, AbstractMvp provides PresenterHolder abstraction, which can be implemented with android ViewModels, Loaders and other lifecycle persistence mechanisms.

ABSTRACT MVP WORKING MECHANISM

Here we have a View interface that is implemented by viewController (Activity or Fragment) and a Presenter. View contains some methods methodA(), methodB(), ... methodN() that are implemented by viewController. When presenter getting created, it start some background jobs, after finishing them, it notifies UI about new changes by calling view.methodB() method. Below is the rough description of steps how viewAction with methodB() will be delivered to UI.

  1. Presenter creates new ViewAction closure with methodB() and send it via ViewActionDispatcher. Code snippet with Kotlin will look like this
// Create the ViewAction for methodB
val actionMethodB = IViewAction.fromLambda() { view ->
  view.methodB()
}
 // Notify viewActionDispatcher about actionMethodB
viewActionDispatcher.onViewAction(actionMethodB)
  1. ViewActionDispatcher will send the viewAction to ViewActionObserver, which contains view instance. Depending from ViewActionDispatcher implementation, viewActions can be cached, if the view is detached, and will be sent to UI when the view will become attached again.
// Sending actionMethodB to ViewActionObserver 
viewActionObserver.onInvoke(actionMethodB)
  1. After receiving actionMethodB instance, ViewActionObserver executes it by passing the view instance.
// Executing actionMethodB inside ViewActionObserver
val view = viewHolder.get() // recieving view instance
actionMethodB.invoke(view) // executing actionMehtodB ViewAction
  1. When actionMethodB is getting executed, the methodB() will be called on our viewController (Activity or Fragment)

ABSTRACT MVP MAIN COMPONENTS

Abstract MVP is consist from a several abstract components, that need to be implemented. Here is the list of them

Components That are related with View

1. ViewAction

2. ViewActionDispatcher

3. ViewActionObserver

Components That are related with Presenter

1. PresenterHolder

2. PresenterLifecycleHandler

Lets Discuss them separately.

ViewAction

ViewAction is a generic interface IViewAction<V:IView> with single method invoke(view: V) where V is the generic type that is inherited from the base IView interface. ViewActions are created inside presenter and passed to viewActionDispatcher. ViewActionDispatcher send them to ViewActionObserver, where invoke(view: V) method will be called.

ViewActionDispatcher

ViewActionDipatcher is a generic interface IViewActionDispatcher<V:IView> responsible for viewActions delivery to ViewActionObserver. This interface contains two methods. First one is setViewActionObserver(viewHolder: ViewHolder<V>, viewActionObserver: IViewActionObserver<V>) which is called every time when new view is attached. With First argument viewholder we can get view instance by calling viewHolder.get() method. When the viewController will be destroyed view instance will be automatically removed from viewHolder container. Second argument is viewActionObserver instance. We can send view actions to viewActionObserver by calling viewActionObserver.onInvoke(viewAction) and passing viewAction instance. Second method is onViewAction(actionType: ActionType, viewAction: IViewAction<V>), which is calling from presenter, every time when we need to pass new viewAction. ActionType is an enum with values are STICKY and IMMEDIATE. STICKY - When viewActionDispatcher receives viewActions and in that time the view is already detached, the viewActions will be added in to queue and delivered when the view will become attached again. IMMEDIATE - ViewActions will be delivered only if view is attached. If view is detached action will be lost.

ViewActionDispatcher can be implemented with RxJava or with a LiveData from Android arcitecture components.

ViewActionObserver

ViewActionObserver is a generic interface IViewActionObserver<V : IView> with two methods. First one is onCreate(viewHolder:ViewHolder) which is calling by framework. Here viewHolder instance we need for invoking received viewActions . Second one is onInvoke(viewAction: IViewAction<V>) this method is called by viewActionDispatcher.

PresenterHolder

PresenterHolder is a generic interface IPresenterHolder<V : IView, P : Presenter<V>> with tree methods (put, get, hasPresenter). All this methods are going to be called by framework. The main point of this container class is to make presenter instance persistence from viewController lifecycle scope. This Interface can be implemented with Android Loaders api or with ViewModels from Android arcitecture components.

PresenterLifecycleHandler

PresenterLifecycleHandler an interface IPresenterLifecycleHandler with one method onCreate(presenterLifecycle: IPresenterLifecycle). This method is called by framework. Here we receive presenterLifecycle instance, which has four methods

    /**
     * onViewAttach, will be called with activity onCreate
     */
    fun onViewAttach()

    /**
     * onViewStop, will be called with activity onStart
     */
    fun onViewStart()

    /**
     * onViewStop, will be called with activity onStop
     */
    fun onViewStop()

    /**
     * onViewDetach, will be called with activity onDestroy
     */
    fun onViewDetach()

PresenterLifecycleHandler's implementation can be done with custom activity lifecycle callback mechanism or it will be more easy to implement with a Lifecycle component from Android arcitecture components.

Presenter also have one more lifecycle method onCreate(), which is called by framework only once, when presenter instance is created, and all components are bound together.

BINDING ALL TOGETHER

AbstractMvp library provides Mvp.Factory<V:IView, P:Presenter> generic interface. Factory class must implement from Mvp.Factory<V:IView, P:Presenter> and override all methods and returns already implemented components. To get presenter instance call Mvp.from(factory:Factory<V,P>) method and pass your factory instance.

SUMMARY

AbstractMvp is The abstraction layer for MVP architecture. It provides the base structure for MVP and allow to define custom MVP implementation.

AbstractMvp Implementation With Android Arcitecture components

Download

Gradle

Add to project level build.gradle

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

Add dependency to app module level build.gradle

dependencies {
    implementation 'com.github.RobertApikyan:AbstractMvp:1.0.3'
}

Maven

<repositories>
 <repository>
  <id>jitpack.io</id>
  <url>https://jitpack.io</url>
 </repository>
</repositories>

Add dependency

<dependency>
 <groupId>com.github.RobertApikyan</groupId>
 <artifactId>AbstractMvp</artifactId>
 <version>1.0.3</version>
</dependency>

Done.

License

Copyright 2018 Robert Apikyan

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.