The development of Themeable has been started on 12-april 2019 during GSOC 2019 , special for Rocket.Chat Android

HOW TO INSTALL

Include jitpack to your repositories

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

Add the themeable to your project

Latets version on Jitpack

dependencies {
        implementation 'com.github.Adizbek:Themeable:${themeable.version}'
}

HOW TO USE

First create our theme. Theme.java

class Theme(val name: String, val manager: ThemeManager<Theme>) : ThemeInterface(name, manager) {
    // default values for styles
    override val themeValues: HashMap<String, Int>
        get() = hashMapOf(
            Pair(KEY_ACTION_BAR_BACKGROUND_COLOR, Color.parseColor("#ffffff")),
            Pair(KEY_ACTION_BAR_TITLE_COLOR, Color.parseColor("#000000")),
            Pair(KEY_STATUS_BAR_COLOR, Color.parseColor("#ffffff")),

            Pair(KEY_DIALOG_LIST_ICON, Color.parseColor("#000000")),
            Pair(KEY_DIALOG_LIST_TITLE_COLOR, Color.parseColor("#000000")),
            Pair(KEY_DIALOG_LIST_TEXT_COLOR, Color.parseColor("#000000")),
            Pair(KEY_DIALOG_LIST_BACKGROUND, Color.parseColor("#ffffff"))
        )

    // we define all style names here 
    companion object {
        val KEY_ACTION_BAR_BACKGROUND_COLOR = "ActionBarBackgroundColor"
        val KEY_ACTION_BAR_TITLE_COLOR = "ActionBarTitleColor"
        val KEY_STATUS_BAR_COLOR = "StatusBarColor"
        val KEY_DIALOG_LIST_ICON = "DialogListIcon"
        val KEY_DIALOG_LIST_TITLE_COLOR = "DialogListTitleColor"
        val KEY_DIALOG_LIST_TEXT_COLOR = "DialogListTextColor"
        val KEY_DIALOG_LIST_BACKGROUND = "DialogListBackground"
    }
}

// example of ThemeListener interface
object Drawables : ThemeListener {
    override fun bindStyles(): Array<ThemeBinder> {
        return arrayOf(
            ThemeBinder(
                drawable = saveIcon,
                key = Theme.KEY_STATUS_BAR_COLOR
            ),
            ThemeBinder(
                drawable = addIcon,
                key = Theme.KEY_STATUS_BAR_COLOR
            ),
            ThemeBinder(
                drawable = personIcon,
                key = Theme.KEY_DIALOG_LIST_ICON
            )
        )
    }

    lateinit var saveIcon: Drawable
    lateinit var addIcon: Drawable
    lateinit var personIcon: Drawable

    fun loadResources(manager: ThemeManager<Theme>, context: Context) {
        val rs = context.resources

        saveIcon = rs.getDrawable(R.drawable.ic_save_white_24dp)
        addIcon = rs.getDrawable(R.drawable.ic_add_alert_white_24dp)
        personIcon = rs.getDrawable(R.drawable.ic_account_circle_white_18dp)

        manager.registerListener(this)
        manager.applyStyles(this)
    }
}

Setup theme manager in our application

class ThemeApplication : Application() {
    override fun onCreate() {
        super.onCreate()

        themeManager = ThemeManager(
            this, // context
            Theme::class.java, // theme class which we created, all defined styles will be here
            fileExtension = "rchatheme" // theme file extension, this will be used while save/loading theme files from filesystem
        )

        registerActivityLifecycleCallbacks(themeManager); // register listener for activity lifecycle

        Drawables.loadResources(themeManager, this)
    }

    override fun onTerminate() {
        super.onTerminate()

        this.unregisterActivityLifecycleCallbacks(themeManager) // unregister listener for activity lifecycle
    }


    companion object {
        lateinit var themeManager: ThemeManager<Theme> // you can access theme manager from everywhere
    }
}

HOW TO USE IN ACTIVITY

class MainActivity : AppCompatActivity(), ThemeListener {
    
    //bind our style to views
    override fun bindStyles(): Array<ThemeBinder> {
        return arrayOf(
            // binds Theme.KEY_ACTION_BAR_TITLE_COLOR to toolbars text color
            ThemeBinder( 
                toolbar,
                ThemeBinder.Flag.COLOR,
                Theme.KEY_ACTION_BAR_TITLE_COLOR
            ),
            // binds Theme.KEY_ACTION_BAR_BACKGROUND_COLOR to toolbars background color
            ThemeBinder(
                toolbar,
                ThemeBinder.Flag.BACKGROUND_COLOR,
                Theme.KEY_ACTION_BAR_BACKGROUND_COLOR
            ),
            // binds Theme.KEY_DIALOG_LIST_BACKGROUND to list background color
            ThemeBinder(
                list, // RecyclerView
                ThemeBinder.Flag.BACKGROUND_COLOR,
                Theme.KEY_DIALOG_LIST_BACKGROUND
            ),
            // binds Theme.KEY_STATUS_BAR_COLOR to fab background color
            ThemeBinder(
                fab, // FloatingActiveButton
                ThemeBinder.Flag.BACKGROUND_COLOR,
                key = Theme.KEY_STATUS_BAR_COLOR
            ),
            // just listen for Theme.KEY_STATUS_BAR_COLOR
            ThemeBinder(key = Theme.KEY_STATUS_BAR_COLOR) { color ->
                // your logic 😏, very dynamic isn't?
            
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                    window.statusBarColor = color
                }
            }
        )
    }
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
      
        ...
        
        ThemeApplication.themeManager.applyStyles(this)
    }
    
    
    override fun onResume() {
        // We need to define theme listener in order to be aware about theme/style changing
        ThemeApplication.themeManager.registerListener(this)

        super.onResume()
    }

    override fun onPause() {
        ThemeApplication.themeManager.removeListener(this)

        super.onPause()
    }
}

HOW TO USE IN VIEWHOLDER

Example

THE POWER OF THEMEABLE

Themeable is very dynamic and flexible. You can style every thing in your app and has internal theme editor.

Ways of style binding

ThemeBinder( // binds key to view's text color
    view,
    ThemeBinder.Flag.COLOR,
    key
)

ThemeBinder( // condition based key
    view,
    ThemeBinder.Flag.COLOR,
    keyProvider = {
        return@ThemeBinder if (System.currentTimeMillis() % 2 == 0L) Theme.KEY_DIALOG_LIST_TITLE_COLOR
        else Theme.KEY_DIALOG_LIST_TEXT_COLOR
    }
)

// custom logic
ThemeBinder(key = Theme.KEY_STATUS_BAR_COLOR) { color ->
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        window.statusBarColor = color
    }
}