Nucleus is a simple Android library, which utilizes the Model-View-Presenter pattern to properly connect background tasks with visual parts of an application.

MVP introduction article

Some time has passed since Model-View-Presenter and RxJava completely superseded Loader and AsyncTask in our applications.

But there are still some defects in our applications even when using such advanced technologies:

• An application is unable to continue a background task execution after a configuration change.
• An application does not automatically restart a background task after a process restart.

While most applications work without such capabilities, their absence is an obvious bug that just sits there and waits for a user who pressed "Login" button while being in a subway and switched to another application because his network connection was too slow. Bugs that almost any application produce in such cases are numerous.

Android docs are covering such problems very briefly, take a look at: Processes and Threads - 4. Background process "If an activity implements its lifecycle methods correctly, and saves its current state, killing its process will not have a visible effect on the user experience, because when the user navigates back to the activity, the activity restores all of its visible state."

This is not true - there WILL be a visible effect because we're not restoring background tasks. The application will restore it's visual state, but it will forget what it is doing. So, if an application restores a progress bar, but does not restore the background task itself - a user will see the usual "progress bar forever" bug.

• In case of configuration change Nucleus automatically re-attaches all running background tasks to the new View. The application will not forget what it is doing.

• In case of process restart Nucleus automatically restarts background tasks. Even when running on a low memory device or waiting for a long running background task completion, the application is still reliable.

• The entire library has been built keeping The Kiss Principle in mind. Anyone can read and understand it easily.

• The library does not depend on Dagger, you don't need to write a whole class just to inject a presenter. One annotation is all you need. Despite presenters are instantiated without Dagger, their dependencies can still be injected.

• Presenter in Nucleus is an external class that does not depend on View, this automatically prevents any troubles that are connected with activity context leaks.

At the moment of the first release, the library main idea was to be the simplest possible MVP implementation.

A couple of months later, I finally realized that RxJava has became the tool number one for smart background threads handling, so RxPresenter appeared. Since that moment, the main focus shifted in the direction of RxJava support.

The correct lifecycle handling was something that seemed obvious to me from the beginning, so I did not make an accent on this feature in the library description. However, since those times, more MVP libraries appeared, now I need to differentiate Nucleus from other implementations. The library description became: "Nucleus is a simple Android library, which utilizes the Model-View-Presenter pattern to properly connect background tasks with visual parts of an application."

dependencies {
    compile 'info.android15.nucleus:nucleus:2.0.4'
}

For additional view classes NucleusSupportFragment, NucleusFragmentActivity include:

dependencies {
    compile 'info.android15.nucleus:nucleus-support-v4:2.0.4'
}

For additional view classes NucleusActionBarActivity, NucleusAppCompatActivity include:

dependencies {
    compile 'info.android15.nucleus:nucleus-support-v7:2.0.4'
}

Hint: you can just copy/paste that classes code into ANY View class to keep your View classes hierarchy as you like to.