If you're not careful, your Android activities can get crippled with too much functionality. And the hard part is refactoring the code that manages views. That's what the Activity is supposed to do.

Google developers recommend organizing views in Fragments. All the Activity should do is manage the Fragments' lifecycle.

But some developers are favouring custom views. The Square development team wrote about it in Advocating Against Android Fragments (the discussion). The main argument is the over-complicated Fragment lifecycle.

class CustomView
@JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0,
    defStyleRes: Int = 0
) : FrameLayout(context, attrs, defStyleAttr, defStyleRes) {
     init {
        inflate(context, R.layout.view_custom, this)
     }
}

At Bloco we like to create a BaseView that all our custom views extend. That way, we can simplify dependency injection, as well as do other useful things that we will leave out for this article.

abstract class BaseView
@JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0,
    defStyleRes: Int = 0
) : FrameLayout(context, attrs, defStyleAttr, defStyleRes) {

    protected open val activity get() = context as BaseActivity
    protected val component get() = activity.component

}

It can also be useful to use custom attributes on a XML.

<io.bloco.template.shared.ui.AvatarImageView
        android:id="@+id/avatar"
            android:layout_width="20dp"
            android:layout_height="20dp"
            android:contentDescription="@string/avatar"
            app:hasBorder="false" />

Having declared the custom attribute "hasBorder", we can use it with our custom view:

class AvatarImageView
@JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0,
    defStyleRes: Int = 0
) : BaseView(context, attrs, defStyleAttr, defStyleRes) {

    private var hasBorder = true

    init {
        inflate(context, R.layout.view_avatar_image, this)

        attrs?.let {
            val a = context.obtainStyledAttributes(it, R.styleable.AvatarImage)
            if (a.hasValue(R.styleable.AvatarImage_border)) {
                hasBorder = a.getBoolean(R.styleable.AvatarImage_hasBorder, true)
            }
        }

        borderView.isVisible = hasBorder
    }
}

Need to handle configuration changes? There's something similar to Activities, using Parcelable:

override fun onSaveInstanceState(): Parcelable? {
    return super.onSaveInstanceState()
    // Save data here
}

override fun onRestoreInstanceState(state: Parcelable?) {
    super.onRestoreInstanceState(state)
    // Restore data here
}