4.1 How to Create UI?
4.2 Common UI Widgets
4.2.1 TextView
4.2.2 Button
4.2.3 EditText
4.2.4 ImageView
4.2.5 ProgressBar
4.2.6 AlertDialog
4.3 Three Basic Layouts
4.3.1 LinearLayout
4.3.2 RelativeLayout
4.3.3 FrameLayout
4.4 Customize the Widgets
4.4.1 Include Layout
4.4.2 Create Customized Widgets
4.5 ListView
4.5.1 Simple Demonstration of ListView
4.5.2 Customize ListView UI
4.5.3 Optimize the Efficiency of ListView
4.5.4 Click Event in ListView
4.6 RecyclerView
4.6.1 Basics About RecyclerView
4.6.2 Scroll Horizontally and Waterfall Flow Layout
4.6.3 RecyclerView Click Event
4.7 Best Practice to Build UI
4.7.1 Create 9-Patch Image
4.7.2 Build Beautiful Chat User Interface
4.8 Kotlin Class: Lateinit and Sealed Cass
4.8.1 Lateinit Variables
4.8.2 Optimization with Sealed Class
4.9 Summary and Comment