implementing interface with fragment, adapter, and activity

Step one is?

Create the interface in the fragment. declare a method such as onAddButtonClicked()

step five?

In adapter's ViewHolder class, set the view we want to listen for a click event onClickListener and call the interface object's method withing this onClickListener

step three?

In the Activity that implements/extends the interface, override the interface's method such as onAddButtonClicked. Define what is does such as starting a new activity

step two?

The activity that uses the interface should implement/extend fragmentName.interfaceName

What was the flow of implementing an interface in the note app?

The activity, which contains a fragmentContainer such as a FrameLayout, has a fragmentTransaction which decides to display note fragment or task fragment depending on which is clicked from the nav menu item list at the bottom of the activity. Each fragment has a AddNote/task text view we use as a button. We need to know when that addNote/task text view is clicked. So we have to send the click info from the adapter to the activity. To do this the adapter must call the interfaces method passing an identifier to the activity that implements the interface.

step four?

The adapter class needs to receive the interface as an object and generate it as property(val). We do this by passing the interface object in the adapter's constructor.

Why do we use an interface?

To shuttle information through activity/fragments. The adapters for our note and task received interface listener objects. We used these object's interface method (onAddNote/OnAddTask) in the ViewHolder inner class inside of view.onClickListeners (views being the TextView for add note/task) We sent const key codes through these listeners interface methods to differentiate between a note fragment and a task fragment.

We need to override the fragment that declares the interface listener's onAttach method. why?

because when the fragment is attached to the activity the activity needs to implement this listener interface to use it and define the interface's methods. This is why the activity extends the interface.

How does the interface work for the note app?

declare interface in fragment. make activity that uses fragment implement/extend the interface. DEFINE the interfaces method. The adapter class's ViewHolder INNER class is where we define onClickListeners and methods to set views. So we call the interface object it receives method here, passing the activity an identifier for note fragment or task fragment.

activity > fragment > adapter > recycler view

fragment declares interface, activity implements it, adapter receives interface object, calls objects interface method, passes activity note/task identifier, activity passes identifier to create activity

interface { fun onNoteClick(identifier: String) } explain this interface and where it would be defined?

in the fragment that needs to communicate with an activity that is using it. The activity will implement this interface and override the onNoteClick method. passing data to another activity.

What should a recycler view adapter do with an interface defined in a fragment? understand that the adapter has to use the interface onClick method because in the note app our fragment used a recycler view. We must use an adapter with that recycler view. The adapter's ViewHolder inner class takes care of click events so the interface method must go there in order to react when add note/task is clicked on the recycler view.

the adapter needs to accept the interface object and use its onAdd method to pass data to the activity that implements the interface.