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My everyday Android practice demos with Kotlin in 100(far and far more...) days.

39. Image Puzzle Game

Date: 2018-8-10


What I learned from this demo:

  • Make a simple image puzzle game with bitmap data operations: scale, draw, clip and so on
  • Use the powerful BRVAH library to make a simple RecyclerView with XML layout
  • Now remove the support library and migrate to androidX packages, so Anko layout is not supported right now

PS: Restart(cold reboot) simulator to make the downloaded images appear in gallery.

# while build failed with this problem:
# Cause: delight/rhinosandox/RhinoSandboxes
# Try run the command in terminal:

gradlew clean assemble -stacktrace

Resource: How to Build a Jigsaw Puzzle Android Game

38. Simple Game With LibGdx

Date: 2018-7-26


What I learned from this demo:

  • Build simple game in Android with libgdx framework
  • Manage multi scenes in the game with Stages and Camera and Sprites
  • Use Box2D to do simple physics simulation in the game

37. Basic Unit And UI Test

Date: 2018-7-25


What I learned from this demo:

  • Basic unit test with JUnit4, and Espresso test framework in Android
  • Use mockK to do Kotlin unit test: mock, spy, function callback captures and verify, ect
  • Simple UI test in Android with Espresso and barista library: find view, click, recyclerview test and waiting and so on

Resource: mockK

36. Service

Date: 2018-5-17


What I learned from this demo:

  • Create Service in Android app with IBinder, send notification background
  • Use Guideline and Barrier in ConstraintLayout with Anko Layout
  • Switch threads in RxAndroid, and in doOnComplete

PS: To correctly use Guideline in constraint layout as the item ui in RecyclerView, I add the code bellow to make sure the layout renders expectedly:

constraintLayout {
    layoutParams = ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT)
    guideline {
        id = ID_GUIDELINE
    }.lparams(width = matchConstraint, height = matchConstraint){
        orientation = ConstraintLayout.LayoutParams.VERTICAL
        guidePercent = 0.25f
    //... other code

35. Reactive Text Search

Date: 2018-5-2


What I learned from this demo:

  • Create Observable from buttons and text changes, and merge them together
  • Switch work threads, use doOnNext to show progress bar, and dispose them when needed
  • Use arrays in XML resource, change the button appearance use the theme of Widget.AppCompat.Button.Colored

34. Basic Material Animation

Date: 2018-3-11


What I learned from this demo:

  • Basic material animations for Fragment: enter/exit transition, shared element trasition
  • Use coroutines to do time-consuming process: async, await in launch coroutines scope
  • Build animations in ConstraintLayout use simple and powerful ConstraintSet and Transition
  • Single activity as a container with multiple fragments

Resource: Android KTX library Keyframe Animations with ConstraintLayout and ConstraintSet PS: While use shared element between fragments, I notice that, the 1st: add will not work but replace works, and 2nd: I set transitionName in the CardView instead of directly in the ImageView, which is the sub-view of CardView, that works!

33. ObjectBox And Coroutines

Date: 2018-3-7


What I learned from this demo:

  • Work with ObjectBox to do the operations of databases
  • Try to use Kotlin Coroutines to simulate some time-consuming process, it's just a test
  • Create the custom Application, use open source toast: Toasty, use NestedScrollView in CoordinatorLayout

Resource: ObjectBox API A test project, lost of functionalities are not accomplished yet.

32. Basic Android MVP

Date: 2018-3-1


What I learned from this demo:

  • Use the basic MVP pattern in Android project, to make code clean and testable
  • Understand and use the abstract class and abstract methods
  • The data binding in view, use this library: KotlinAndroidViewBindings (I just copied some code in my project.)

Resource: KotlinAndroidViewBindings

31. Retrofit And RxAndroid

Date: 2018-2-6


What I learned from this demo:

  • Try with Retrofit and RxAndroid/RxJava to populate data in web service
  • No XML layout now, try to work with pure Anko layouts, and the awesome Anko ConstraintLayout library
  • How to change the layout in RecyclerView, and smooth scroll to the desired position
  • Anko layout with Coordinator Layout, CardView, AppBar Layout, Toolbar and so on in design support library
  • Pre-load or pause-load behavior in Glide image loader with RecyclerView while scrolling

Resource: Anko ConstraintLayout Glide: RecyclerView integration library

30. A Simple Custom View Group

Date: 2018-1-29


What I learned from this demo:

  • It works like a charm!!! Five days cost to finish my little simple ViewGroup! That deserves.
  • Got the basic idea of the processes of measure, layout, touchEvent, interceptEvent, and custom child layout parameters
  • Use the scroller to make the movement much smooth
  • Let the ViewGroup support click event and long click events

29. A Map Demo

Date: 2018-1-23


What I learned from this demo:

  • Show map, display marker, animate camera, search, deal with the latitude and longitude with A Map API
  • Fullscreen control, show and hide the soft keyboard
  • Work with the AutoCompleteTextView widget

Resource: A MAP

28. Custom View The Switch

Date: 2018-1-21


What I learned from this demo:

  • Custom view with basic workflow: measure, layout, draw and touch event handle
  • Add custom properties or attributes in XML of view
  • The basics of drawing api in Android with: path, paint, canvas

27. Play With Audio Assets

Date: 2018-1-11


What I learned from this demo:

  • No XML layouts, the UI is completely replaced with Anko layout codes
  • Work with assets in Android, and use AssetManager to do asset management
  • Use SoundPool to play tiny wav audio files
  • The basic knowledge of Anko layouts, pure code to make views

26. Better Practice Fragment (Part.1)

Date: 2018-1-8


What I learned from this demo:

  • Use RecylcerView list item animations with XML resource
  • Understand the layout_behavior in CoordinatorLayout and layout_anchor property
  • Try to use Fragment instead the Activity for better practise, it makes ViewPager very esay to build
  • Work with the alert dilog with custom view

The refactor is not so easy for me, a lot of functionalities is not finished, and I will try to get that done later.

25. Image Uploader

Date: 2017-12-29


What I learned from this demo:

  • Work with OKHttp to post data: upload files, get and send cookies, retrive the result
  • Use XML Shape to create nice controls such as buttons
  • Crop image and get the bitmap data through FileProvider in API greater than 24
  • Use view animations, Gson to analysis json string, indeterminateProgressDialog and alert in anko

Realy thanks to the guy in Weixin group: @���е���ؤ���� for solving my code problem, while reuse the animation XML will cause wried things!

24. Photo Wall

Date: 2017-12-26


What I learned from this demo:

  • Get images throught network, decode stream and display
  • Use LruCache to cache the bitmap data for quick loading and recylcling data usage
  • The same Activity is setted as both the Detail activity and Add New activity
  • Load data from database in the asynchronized way

If too much photos loaded, will the app get the changce to crash for OOM? I should try to figure it out!

23. Parcelable Data Objects

Date: 2017-12-23


What I learned from this demo:

  • Use Parcelable objects for data passing between activities
  • Try Android unit test with: Instrumented Test and Unit Test
  • Data class used both as Parcelable data object and Room database entity
  • Solve two problems through Gradle error, failed to create directory and Empty test suite

A lot of functionalities are not implemeted yet in this app, and I will finish that in my next days, hold on please! :)

22. Simple View Pager

Date: 2017-12-16


What I learned from this demo:

  • Work with ViewPager and TabLayout together to display walk through pages
  • Use FragmentStatePagerAdapter as the ViewPager adapter and, the fragments
  • Finish the activity so that make sure it is removed from the stack

Resource: ViewPager Tutorial: Getting Started in Kotlin

21. The Floating Window

Date: 2017-12-16


What I learned from this demo:

  • No layout XML files, but replace with the anko layout library to create views
  • Use WindowManager to display floating views on the window
  • Deal with the back button pressed to hide the activity, prevent from finishing the app

After 2 months at last! Still 2 problems or questions: 1. If back pressed and app is killed, then the android.view.WindowLeaked exception throws, how to solve? 2. In the emulator, if the drag and drop event happens outside, then the position of the window will be some wried.

20. Simple Search Web View

Date: 2017-10-18


What I learned from this demo:

  • Work with WebView, set the client as WebViewClient and WebChromeClient
  • Use the ToolBar instead of ActionBar, try SearchView in the tool bar
  • Save and retrieve list items (StringSet) in shared preferences
  • Add or remove item in RecyclerView, handle long click events on list item
  • Deal with the WebView in NestedScrollView through the library: NestedScrollWebView in Github

Resource: NestedScrollWebView

19. Downloader With Notifications

Date: 2017-10-14


What I learned from this demo:

  • Use the basic notifications in Android
  • The asynchronized task with doAsync and uiThread in Kotlin
  • Basic file and stream operations in Android

18. Basic File Operation

Date: 2017-10-4


What I learned from this demo:

  • Use SharedPreferences to store and retrieve simple data
  • Basic file operations on Android system, with openFileInput and openFileOutput
  • Set data in the activity result and return

17. Simple Broadcast Receiver

Date: 2017-09-27


What I learned from this demo:

  • Use one of the most four important components in Android: Broadcast Receiver
  • Extension functions in Kotlin with AppCompatActivity
  • Try the open-source library: EventBus to post and handle events, and also the CircleImageView
  • Reduce the redundant of layout by using <inlucde> tags

I am still not very clear with Android BroadcastReceiver, I found that it sometimes(especially for the single app development) can be replaced with EventBus through publish/subscribe pattern, is that right?

16. Self Adaption

Date: 2017-09-12


What I learned from this demo:

  • Use the Fragments in the Activities
  • Specify different layouts for different size or screen orientation (layout-land and layout-large)
  • Use the empty view element as spacer or divider (be careful of the tag, it is View not view!)
  • Dynamically set the visibility of view

Till now I have no idea of using the savedInstanceState variable to make the data consistent while rotate the screen orientation, I should try it out later.

15. Database with Room

Date: 2017-09-04

ProjectDatabaseRoom.gif ProjectDatabaseRoom_adb_shell_sqlite3.gif

What I learned from this demo:

  • Use the Room Persistence Library for the basic database operations: INSERT/DELETE/UPDATE/QUERY
  • Work with data class in Kotlin and the let lamda, and the annotations
  • Convert date types to string types, and vice versa by using SimpleDateFormat or DateFormat.getDateInstance()
  • Use adb shell and sqlite3 command to query the data in emulator local system files:
$ adb quit

# for more than one device found here
$ adb devices
$ adb -s <emulator name> shell
$ cd data/data/

$ sqlite3
$ .open <dbname.db>
$ .tables
$ SELECT * FROM <table name>

14. Activity Animations

Date: 2017-09-01


What I learned from this demo:

  • Transitions between activities use overridePendingTransition
  • Work with animation xml resource file, the difference of "50%" and "50%p" (relative to parent view)
  • Override onBackPressed method to finish the activity

13. Simple Activity with Intent

Date: 2017-08-31


What I learned from this demo:

  • Dealing with the custom item click handler of RecyclerView
  • Start an intent to show another Activity by startActivityForResult
  • Get the result from another activity through method of onActivityResult

12. Simple Animations with Custom View

Date: 2017-08-30


What I learned from this demo:

  • Custom view with custom attributes (declared in the xml value file)
  • Use onMeasure to set the correct size of view
  • Use onDraw to display the paint on the canvas
  • Work with the basic object animator and animator-set
  • The importance of lazy properties in Kotlin, think about the code:
//the [sunColor] initialized here will be changed later in the constructor through xml user attributes.
private var sunColor = Color.RED
//the paint directly initialized will not be the expected one, as the [sunColor] will change later for xml attributes!
private val paint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
    this.color = this@SunView.sunColor
    this.isAntiAlias = true
//by using the lazy properties, the paint will be all right with the [sunColor] property!
private val paint by lazy {
    Paint(Paint.ANTI_ALIAS_FLAG).apply {
        this.color = this@SunView.sunColor
        this.isAntiAlias = true

11. Simple Scalable ImageView

Date: 2017-08-28


What I learned from this demo:

  • Multiple constructors from base class inheritance in Kotlin
  • The basic knowledge of custom view: onLayout (left, right, top, bottom)/setFrame/onTouchEvent (Here I should always return true for receiving other touch events)
  • Multi-touch handle on views: use event.actionMasked instead of event.action

This is a bad-experienced project(view), I think I have to improve that in the next days while learning.

11. Simple ASynchronized Works

Date: 2017-08-17


What I learned from this demo:

  • Try to figure out the differences of usage between Handler and AsyncTask in Android
  • Download file from server via OkHttp and read bytes from InputStream
  • RandomAccessFile for writing file content from specified positions

Till now I can't figure out a solution to pause/resume the downloading tasks, and I will try it later.

10. Swipe Refresh RecylcerView

Date: 2017-08-16


What I learned from this demo:

  • Work with SwipeRefreshLayout and RecyclerView
  • Basic AlertDialog and Snackbar usage
  • Custom header and footer item in RecyclerView (It looks a little weird!)

9. Simple Video Player

Date: 2017-08-14


What I learned from this demo:

  • The first time explore the MediaPlayer with SurfaceView
  • Got idea of LayoutParams and its simple properties (ConstraintLayout.LayoutParams)

8. Basic Material Design

Date: 2017-08-12


What I learned from this demo:

  • Basic material design elements: DrawerLayout, NavigationView, CoordinatorLayout, AppBarLayout with Toolbar and FloatingActionButton
  • Try to use the open source Android libraries of RxAndroid, OkHttp, Gson and Glide, ect.
  • DrawerLayout must work with a child with layout_gravity property specified.
  • Gson tokens with types: object : TypeToken<List<Turns>>() {}.type is the right way.

Resource: RxAndroid, OkHttp, Gson, Glide

7. Recycle Image Loader

Date: 2017-08-11


What I learned from this demo:

  • CardView is very cute, isn't is? (I hate the gap between image nad text!)
  • Load json data through HttpURLConnection and display view with ViewStub
  • Use doAsync{} and uiThread{} to do asynchronized task in Kotlin
  • Read InputStream in Kotlin and convert string data to JSONObject

6. Basic RecycleView

Date: 2017-08-09


What I learned from this demo:

  • The very basics of RecycleView
  • RecycleView with custom ViewHolder and Adapter, and layout managers
  • Using lazy delegates , and Pair<out A, out B> in Kotlin

In fact it shows the unexpected results, but I will give more effort to the RecycleView app next time.

5. Pick Image

Date: 2017-08-08


What I learned from this demo:

  • Start a intent and get the result from that
  • Work with local images and camera basics
  • Display bitmap data on an ImageView

4. My Location

Date: 2017-08-06


What I learned from this demo:

  • Work with LocationManager, get GPS providers and locations
  • Got to know how to request specified Permissions at RunTime
  • Use HttpUrlConnection to fetch data with url and read the input streams
  • The LAMDA of thread and runOnUiThread

My network is not stable, and I really do a lot of hard-code, I think I can fix that later.

3. Tip Calculator

Date: 2017-08-05


What I learned from this demo:

  • Work with EditText and SeekBar
  • The editor of keyboard event handler with EditText
  • Strings to formatted floats and strings remove specified prefix in kotlin

And what I cannot resolve is the focus changes of EditText and auto-hided of keyboard, I hope I can work it later.

2. Tap or Hold Counter

Date: 2017-08-04


What I learned from this demo:

  • Delegates of property in Kotlin
  • Basic usage of Timer and TimerTask
  • Button long click and touch event listener
  • AnkoLogger for test (I have deleted the test code, but the activity has implemented the interface)

1. Tap Counte

Date: 2017-08-03


What I learned from this demo:

  • Menu resource file creation and option menus add to title bar
  • Use anko library to reach UI elements easily in layout
  • Button click handler with lambda in kotlin
  • Change the button and text view appearance in editor
  • Basic usage of Git commands and Github repository with AS 3.0

Resource: anko


My everyday Android practice demos with Kotlin in 100 days.







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