What properties can you add as extensions in Android…

In Android development, extensions (extension functions and properties) allow adding new functionality to existing classes without inheritance or using decorators. This is especially useful when working with standard SDK classes.

Extension Properties are properties that we can add to existing classes. They do not store state; their computed value is determined by a getter.

Examples of using extension properties in Android:

Simplifying access to LayoutInflater:

// Adding an extension property for accessing LayoutInflater
val Context.layoutInflater: LayoutInflater  
    get() = LayoutInflater.from(this)

Now you can use context.layoutInflater instead of LayoutInflater.from(context).

Short property for hiding a View:

// Extension property to set View visibility to GONE
var View.isVisibleGone: Boolean  
    get() = visibility == View.VISIBLE // Getter to check current state  
    set(value) { // Setter to set the state  
        visibility = if (value) View.VISIBLE else View.GONE  
    }

Now you can use view.isVisibleGone = false to hide a View.

Getting screen size in DP:

// Extension property to get screen width in DP
val Context.screenWidthInDp: Int  
    get() = resources.displayMetrics.widthPixels / resources.displayMetrics.density.toInt()

Example usage: context.screenWidthInDp.

Access to SharedPreferences:

// Extension property to get SharedPreferences by name
fun Context.sharedPreferences(name: String): SharedPreferences =  
    getSharedPreferences(name, Context.MODE_PRIVATE)

Although this is a function, it is often used as a property for convenient access: context.sharedPreferences("my_prefs").

Important points about extension properties:

They cannot have backing fields (variables storing values).
They must be defined either with only a getter (read-only) or with a getter and setter (read-write).
They are compiled as static methods, so their call occurs through the owner class.

Basically, in Android, you can add any computed property as an extension that logically relates to an existing class and simplifies its use, avoiding the creation of auxiliary functions or wrapper classes.

What properties can you add as extensions in Android?