Forem: Bigyan Thapa

Gain performance by inline

Bigyan Thapa — Thu, 02 Apr 2020 19:41:59 +0000

Recently watched a video by Florina Muntenescu here, regarding Inline functions in Kotlin. Wanted to share something I learned here:

A function can be inlined with inline keyword. e.g.

inline fun foo(){
}

When a function is marked as inline it is compiled to the call site . This will decrease memory allocation especially when using lambda expressions in kotlin. If a function is not marked as inline , the compiler will create new function object for it. By inlining the function, compiler will copy the implementation to the call site avoiding the requirement to create new function objects.

However, we should be careful when using inline functions. Inlining large functions increases the size of generated code.
For further reference please watch the video on the link.

Thanks!!

Thank you for your support!

Bigyan Thapa — Thu, 02 Apr 2020 16:37:28 +0000

Thank you all the followers and the community. Especial thanks to @tsmrgrg for being my 100th follower. It is both humbling and motivating to receive such support from the community.
In the days to come, I will do my best to contribute more and be of help however way possible.

Thank you!

How important is accessibility for you as a developer?

Bigyan Thapa — Wed, 25 Mar 2020 21:49:45 +0000

This is targeted for Android Developers, but if you have accessibility knowledge in any framework, please feel free to take part.

I am in a process fixing several accessibility issues of my company's app and have been looking at resources, tutorials and articles to learn more.
This discussion in intended to collect some insights on the following areas of accessibility:

How do you feel about accessibility?
How accessible is your android app?
What accessibility issues are you prioritizing?
How are you verifying the accessibility fixes?
Any pending future enhancements on your TODO list?
Any useful resources you want to share :)

Thank you!

WorkManager for Background location updates

Bigyan Thapa — Wed, 11 Mar 2020 03:10:42 +0000

If we are working as Android Developers, almost always we will have some requirement to perform some task in the background. One of the common task is to receive location updates in the background.

Previously, we might have used Evernote Android-job, BroadcastReceivers, PendingIntent, Push notification, JobIntentService, Firebase Job dispatcher or some combination along those lines. But with Google's announcement of deprecating those implementations and moving to WorkManager has given us a deadline to migrate our existing implementation towards that direction.

In this article, I am going to put some light on how to receive location updates in background using WorkManager.

Worker class

class UpdateLocationWorker(context: Context, workerParams: WorkerParameters, private val someRepository: SomeRepository) :
    CoroutineWorker(context, workerParams) {
    override suspend fun doWork(): Result {
        return withContext(Dispatchers.IO) {
            try {
                someRepository.getLocation()
                Result.success()
            } catch (e: Exception) {
                Log.d("$TAG", "Exception getting location -->  ${e.message}")
                Result.failure()
            }
        }
    }

    companion object {
        private const val TAG = "UpdateLocationWorker"
        private const val DEFAULT_MIN_INTERVAL = 15L

        @JvmStatic
        fun schedule() {
            val worker = PeriodicWorkRequestBuilder<LocationUpdateWorker>(DEFAULT_MIN_INTERVAL, TimeUnit.MINUTES)
                .addTag(TAG).build()
            WorkManager.getInstance(getApplicationInstance()) // provide application instance here
                .enqueueUniquePeriodicWork(TAG, ExistingPeriodicWorkPolicy.REPLACE, worker)
        }
    }
}

Note that the default minimum interval is 15 minutes and that is android default. If we set an interval less than 15 minutes, that will get overridden to 15 minutes in runtime. More on that here.

Repository class

class SomeRepository(someDao: SomeDao, someLocationManager: SomeLocationManager, scope: CoroutineScope) {

  suspend fun getLocation() {
        someLocationManager.getUpdatedLocation { location -> onLocationReceived(location) }
    }

    internal fun onLocationReceived(location: Location?) = coroutineScope.launch {

        location?.let { newLocation ->
            saveLocation(LocationData(newLocation))
        }
    }

   suspend fun saveLocation(location: LocationData) {
        dao.saveLocation(location)
    }
}

Location manager class

class SomeLocationManager(val context: Context) {

    fun getUpdatedLocation(block: (Location?) -> Unit) {

        val permission = ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION)

        if (permission == PackageManager.PERMISSION_GRANTED) {
            LocationServices.getFusedLocationProviderClient(context).lastLocation.addOnSuccessListener { location ->
                block.invoke(location)
            }
        } else {
            block.invoke(null)
        }
    }
}

Dao class

@Dao
interface SomeDao {
  @Insert(onConflict = OnConflictStrategy.REPLACE)
  fun saveLocation(location: LocationData)
}

LocationData and utility

data class LocationData(
    val provider: String,
    val time: Long,
    val latitude: Double,
    val longitude: Double,
    val altitude: Double,
    val accuracy: Float
)

fun Location.toLocationData(location: Location) = LocationData(
   provider = "fused",
   time = this.time,
   latitude = this.latitude,
   longitude = this.longitude,
   altitude = this.altitude,
   accuracy = this.accuracy
)

Usage

We could schedule the worker when MainActivity or the Application is started.

class MainActivity : AppCompatActivity() {

  override fun onCreate(savedInstanceState: Bundle) {
    super.onCreate(savedInstanceState)
    UpdateLocationWorker.schedule()
  }
}

Jobs scheduled with WorkManagers are guaranteed to run in the given interval even if the app is closed or force killed.

For further reading, please follow the WorkManger link above.
Also, please feel free to provide feedback in comments.
Thank you!

Kotlin Object Vs Companion Object

Bigyan Thapa — Mon, 09 Mar 2020 00:52:07 +0000

Recently I came across a question during a code-review. It was in the context of a PR where kotlin class and a bunch of functions inside a companion object {} annotated as @JvmStatic for Java interoperability were used. The feedback was "why we can't convert the class into an object and get rid of the companion object {}?".This raised the question, "what is the benefit with that?". Some explanation was done, but I wasn't completely satisfied with the explanation given (by me :)). So, decided to do a bit reading and document the differences, and use-cases for my future reference and for someone who will stumble upon similar question.

Object

Object in kotlin is a way of implementing Singletons. We all have come across the need of Singleton pattern in our career for various use-cases. Well, in kotlin this has been made very straight forward.
e.g.

object MyObject {
  // further implementation
  fun printHello() {
    println("Hello World!")
  }
}

This implementation is also called object declaration. Object declarations are thread-safe and are lazy initialized, i.e. objects are initialized when they are accessed for the first time.

Companion Object

If we want some implementation to be a class but still want to expose some behavior as static behavior, companion object come to the play. These are object declarations inside a class. These companion objects are initialized when the containing class is resolved, similar to static methods and variables in java world.
e.g.

class MyClass {

  // some implementations

  companion object {
    val SOME_STATIC_VARIABLE = "some_static_variable"
    fun someStaticFunction() {
      // static function implementation
    }
  }
}

Summary

Given the above explanation, the use-case completely depends on the problem we are trying to solve. If we need to provide the Singleton behavior, then we are better off with Objects, else if we just want to add some static essence to our classes, we can use Companion objects.

Bonus - Accessing Objects & Companions from Java

@JvmField, lateinit, const, @JvmStatic are handy when it comes to accessing field properties or functions defined in objects or companion objects.
e.g. our object can be something like below

object MyObject {

  @JvmStatic
  fun printStaticHello() {
    println("Static Hello World!")
  }

  fun printNonStaticHello() {
    println("Non-Static Hello World!")
  }
}

From Java world, we can access those functions as:

MyObject.printStaticHello() OR
MyObject.INSTANCE.printNonStaticHello() - this uses the singleton instance

e.g. accessing companion object

class MyClass {

  companion object {
    @JvmStatic
    fun printStaticHello() {
      println("Static Hello World!")
    }

    fun printNonStaticHello() {
      println("Non-Static Hello World!")
    }
  }
}

From Java world, we can access those as:

MyClass.printStaticHello()
MyClass.Companion.printStaticHello()
MyClass.Companion.printNonStaticHello()

Thank you for reading.
Note: Further reading and references, here & here

Mistakes made and lessons learnt - bash to zsh

Bigyan Thapa — Wed, 12 Feb 2020 01:19:10 +0000

Bash to zsh

Recently, I migrated from using bash go zsh as most of us did.

chsh -s /bin/zsh easy right :)

But somehow I managed to break my terminal in the process of setting up AndroidStudio. I am not a shell pro but I like to keep couple of adb and git commands as alias, so that I can use AndroidStudio Terminal or System Terminal to perform quick actions. All, I wanted to do was to add the path to android-sdk and platform-tools to the system path so that all the adb commands would be recognized and life would be simple. But somehow I managed to break it.

These are the steps I took to kind of migrate everything my .bash_profile had over to zsh.

Setting up Android SDK and platform path

create .zshrc file -> nano ~/.zshrc
add the path to zshrc . We can open and edit this file in TextEditor or edit it in the terminal itself like:
- vi ~/.zshrc ,then press i for insert, paste the path, then :wq for write and quit.
- something like below:

export PATH='$PATH:/~YOUR_HOME/Library/Android/sdk'
export PATH='$PATH:/~YOUR_HOME/Library/Android/sdk/platform-tools'

At this point, most of you might already notice the mistake in the above snippet. Somehow, having the quotes broke everything and nothing worked. When I say nothing, I mean the cd, ls, cd .. etc. commands from the system's zsh (/bin/zsh) also didn't work. Once, I delete these two lines, everything would work and I would be where I started, i.e. adb commands wouldn't work.
The key to this was to remove the quotes surrounding the path. Once I removed those, everything started working fine.

export PATH=$PATH:/~YOUR_HOME/Library/Android/sdk
export PATH=$PATH:/~YOUR_HOME/Library/Android/sdk/platform-tools

One way to verify this is to check the path in the terminal, and the path now should include path to android-sdk and platform-tools, this is the command echo $PATH.

Setting up `.zprofile` corollary to `.bash_profile`

create .zprofile file -> nano ~/.zprofile
add the aliases to .zprofile . We can open and edit this file in TextEditor or edit it in the terminal itself like:
- vi ~/.zprofile ,then press i for insert, paste the path, then :wq for write and quit.

Bonus - some aliases that I use

# Git Commands
alias gf='git fetch'
alias gp='git pull'
alias gs='git status'
alias gcd='git checkout develop' #or master if you have master

# Gradle Commands
alias at='./gradlew assembleDebug assembleAndroidTest'
alias allTest='./gradlew assembleDebug testDebugUnitTest'
alias cbc='./gradlew cleanBuildCache'
alias build='./gradlew build'
alias stop='./gradlew --stop'
alias status='./gradlew --status'

# ADB Commands
alias devs='adb devices'
alias kill='adb kill server'
alias restart='adb restart server'

Please comment if there better ways of doing this and feel free to add more helpful aliases.

Thank you!

Simple circular progress indicator

Bigyan Thapa — Sun, 02 Feb 2020 00:17:06 +0000

Simple Circular ProgressView Animation

When it comes to UI and loading data, there is always a requirement to fetch the data we want to load in the UI. It is either from fetching from remote, or local database. And as we all know, fetching data adds latency more often than not, leaves us with a blank screen until the data is ready.

The challenge now is to actually keep the user engaged and provide some context while the data is loading. Most of the times, our first go-to way of indicating that the app is doing something is to throw a ProgressView with a default timeout of 15 seconds or so. In most cases this does the job but this shouldn't always be our go-to way. While there are several ways and recommendations of handling this with more contextual loading screens, placeholders or Facebook's ShimmerLayout , one simple way of adding some context to the progress is to display a ProgressView that actually shows progress, rather than a continuously spinning for 15 seconds.

Let me introduce a simple way that I implemented. This approach is to display an animated circular progress view.

It has following pieces:

Vector drawable for the circle
Animated-vector drawable for the animation
Animation trigger
Actual Animation

Vector drawable for the circle

<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="28dp"
    android:height="28dp"
    android:viewportWidth="28"
    android:viewportHeight="28"
    >
  <path
      android:name="circle"
      android:pathData="M14,1.5C7.1,1.5 1.5,7.1 1.5,14C1.5,20.9 7.1,26.5 14,26.5C20.9,26.5   26.5,20.9 26.5,14C26.5,7.1 20.9,1.5 14,1.5Z"
      android:strokeWidth="3"
      android:fillColor="#00000000"
      android:strokeColor="#88D445"
      android:fillType="evenOdd"
      />
</vector>

Animated-vector drawable for the animation

<?xml version="1.0" encoding="utf-8"?>
<animated-vector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:drawable="@drawable/circle"
    tools:targetApi="21"
    >
  <target
      android:name="circle"
      android:animation="@animator/circle_animation"
      />
</animated-vector>

Animation trigger

From ViewModel

val animationStart = MutableLiveData<Int>()

From Fragment

private fun observeAnimationStart() {
    viewModel.animationStart.observe {
      activity?.let { act ->
        val drawableCircle: AnimatedVectorDrawableCompat? =
          AnimatedVectorDrawableCompat.create(act as Context, R.drawable.animated_circle)
        animateProgressView(drawableCircle)
      }
    }
}

Actual Animation

private fun animateProgressView(drawable: AnimatedVectorDrawableCompat) {
    binding.animationImageView.background = drawable

    val animatable: Animatable2Compat = drawable
    animatable.registerAnimationCallback(object : Animatable2Compat.AnimationCallback() {
      override fun onAnimationEnd(drawable: Drawable?) {
        binding.animationImageView.background = null
      }
    })
    animatable.start()
}

This implementation was done for a simple MVVM architecture. The ViewModel sould expose the ProgressView show/hide state via. LiveData or SingleLiveEvent which is observed by the corresponding Fragment. Now, this fragment is responsile for starting and ending the animation, or when the aimation is done, just assign null for the drawable.

Please refer to the above code sample to get more information on the implementation. Also, please feel free to add comments if you have come across better ways of implementing this.

Note: Due to backward campatibility, I am using AminatedVectorDrawableCompat and Animatable2Compat for drawable. Also, there is no timing. It is simply drawing the path. So, this wouldn't be ideal for long running progress view.

Common android utility functions made easier with kotlin-extensions

Bigyan Thapa — Sun, 29 Dec 2019 16:16:07 +0000

As kotlin has taken over most of Android development ecosystem, by now we all are aware of all the goodies that kotlin offers. One of the most liked goodies is extension-functions.
Following are some of the extension-functions that come in handy in day-to-day android application development.

Showing/ hiding views

fun View.visibleOrGone(show: Boolean = false) {
  this.visibility = if(show) {
    View.VISIBLE
  } else {
    View.GONE
  }

Hide Keyboard

fun View.hideKeyboard() {
  (context.getSystemService(Context.INPUT_METHOD_SERVICE) as? InputMethodManager)?.let { inputManager -> 
    inputManager.hideSoftInputFromWindow(windowToken, 0)
  }
}

EditText after text changed

We can pass the function to be performed after edit text input changes as closure.

fun EditText.afterTextChanged(afterTextChanged: (String) -> Unit) {
  this.addTextChangedListener(object : TextWatcher {
    override fun afterTextChanged(s: Editable?) {
      afterTextChanged.invoke(s?.toString())
    }
    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) { // na
    }
    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) { // na
    }
  })
}

RecyclerView set divider

dividerResId is the divider drawable if we have to provide custom divider.

fun RecyclerView.setDivider(dividerResId: Int? = null, orientation: Int = DividerItemDecoration.VERTICAL) {

  val dividerItemDecoration = DividerItemDecoration(this.context, orientation)

  dividerResId?.let { resId ->
    this.context.getDrawableResource(resId)
      ?.let { divider ->
        dividerItemDecoration.setDrawable(divider)
      }
  }
  this.addItemDecoration(dividerItemDecoration)
}

Accessing resources with ContextCompact

fun Context.getColorResource(colorRes: Int): Int {
  return ContextCompat.getColor(this, colorRes)
}

fun Context.getDrawableResource(drawableRes: Int): Drawable? {
  return ContextCompat.getDrawable(this, drawableRes)
}

TextView extensions to set drawable

fun TextView.setDrawable(
  @DrawableRes
  drawable: Int, start: Boolean, end: Boolean, top: Boolean, bottom: Boolean
) {
  when {
    start  -> this.setCompoundDrawablesRelativeWithIntrinsicBounds(drawable, 0, 0, 0)
    end    -> this.setCompoundDrawablesRelativeWithIntrinsicBounds(0, 0, drawable, 0)
    top    -> this.setCompoundDrawablesRelativeWithIntrinsicBounds(0, drawable, 0, 0)
    bottom -> this.setCompoundDrawablesRelativeWithIntrinsicBounds(0, 0, 0, drawable)
  }
  this.compoundDrawablePadding = 8
}

I hope this will be helpful. I will add more in future. Please provide feedback in comments.

Parcelize in Android using kotlin-android-extensions

Bigyan Thapa — Sun, 29 Dec 2019 01:04:34 +0000

With kotlin-android-extensions we can implement Parcelable in much simpler way using @Parcelize and Parcelable.

Enable android extensions in `app` gradle file

Android extensions are not considered production-ready yet, so we need to turn experimental mode on in app's build.gradle file

androidExtensions {
  experimental = true
}

Parcelize simple `class` or `data class`

For this we need to annotate the class with @Parcelize and implement Parcelable. @Parcelize annotation requires all serializable properties be declared in the primary constructor.
e.g.

@Parcelize
class Book(val author: String, val price: Int): Parcelable

@Parcelize
data class User(val name: String, val age: Int): Parcelable

More advanced serialization logic can be written inside a companion object:

@Parcelize
data class Book(val author: String, val price: Int) : Parcelable {
  private companion object: Parceler<Book> {
    override fun Book.write(parcel: Parcel, flags: Int) {
      // add custom write here
    }
    override fun create(parcel: Parcel): Book {
      // add custom read here
    }
  }
}

Parcelize enums

Enum can also be parcelized starting kotlin-version:1.2.60. This is similar to parcelizing the data classes.

@Parcelize
enum class BookType: Parcelable { HISTORY, DRAMA, FICTION, BIO }

Parcelize sealed classes

sealed and abstract classes can also be parcelized. For this, the parent class needs to implement Parcelable and all the child classes need to be annotated with @Parcelize. e.g.

sealed class Result : Parcelable {

  @Parcelize
  object Failure : Result

  @Parcelize
  object Error : Result

  @Parcelize
  class Success : Result
}

Please leave feedback in the comments.

Generic RecyclerViewAdapter

Bigyan Thapa — Tue, 24 Dec 2019 14:34:13 +0000

Trying to make one adapter fit all RecyclerViews in the application.

While this is not an absolute use-case as we might want different list to behave differently. But the core purpose of RecyclerView is to display the data and be able to scroll through it. Also, when we click on the list-item we possible want to navigate to details for that list-item. While doing this, there will be a lot of redundant code that will be duplicated in all RecyclerView adapters in our codebase.

Below is a basic example of abstracting away the core functionality of a RecyclerView adapter and have the sub-classes take care of the rest. This articles assumes that the readers will have basic understanding of RecyclerView, databinding and kotlin.

abstract class BaseRecyclerViewAdapter<T> : Adapter<ViewHolder>(), {

  var items: List<T> = emptyList()
    set(value) {
      field = value
      notifyDataSetChanged()
    }

  override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder = getViewHolder(parent, viewType)

  override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    if(position in items.indices) {
      (holder as Binder<T>).bind(items[position])
    }

  abstract fun getViewHolder(parent: ViewGroup, viewType: Int): ViewHolder

  interface Binder<in T> {
    fun bind(item: T)
  }
}

Usage

The above abstract RecyclerView adapter can be used in a fragment as follows:

class SomeListFragment {

  private lateinit var adapter: SomeAdapter

  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?) : View? {
    super.onCreateView(inflater, container, savedInstanceState)
    // initialization code here ...
    adapter = SomeAdapter() // initialize adapter here
    // ...
  }

  // rest of fragment implementation

  inner class SomeAdapter : BaseRecyclerViewAdapter<SomeData>() {
    override fun getViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
      val viewBinding: SomeListItemBinding = DataBindingUtil.inflate(layoutInflater, R.layout.some_list_item, parent, false)
      return SomeViewHolder(viewBinding)
    }
  }

  inner class SomeViewHolder(private val viewBinding: SomeListItemBinding) : ViewHolder(viewBinding.root), BaseRecyclerViewAdapter.Binder<SomeData> {

   override fun bind(item: SomeData) {
     /*
       bind data here, we can also assign click listeners
       viewBinding.root.setOnClickListener { ... }
     */
   }
  }
}

Please provide feedback in comments.
Thank you for reading.

Android RecyclerView StickyHeader without external library

Bigyan Thapa — Tue, 24 Dec 2019 13:52:55 +0000

There are several occasions when we need to implement sticky header for some list of data displayed in RecyclerView. And of course, Android doesn't have a native UI component to implement this easily. There are several third-party libraries which we can use to achieve this functionality. But using third party libraries always comes at a cost. There is always a doubt of whether the library we are using will be updated for future versions or not, apart from the additional overhead of LOC and app size that these libraries add.
One simpler way of achieving this same behavior without having to use any third party library is to write a custom RecyclerView ItemDecoration and override onDrawOver(canvas: Canvas, parent: RecyclerView, state: State) function.
Below is the description on how to do that. Please feel free to customize this implementation to meet your requirements:

Custom ItemDecoration

This is a wrapper around ItemDecoration abstract class. As it is stated on the documentation, these ItemDecorations are drawn in the order they were added, before the views and after the items.

In this implementation of the custom decoration, we are going to provide three things as parameter:

RecyclerView adapter
Root view, e.g. the fragment's root where the RecyclerView exists
Layout resource id for the header to be used

class StickyHeaderDecoration<B : ViewDataBinding>(
val adapter: StickyHeaderAdapter<*>, root: View, 
@LayoutRes headerLayout: Int) : ItemDecoration() {

  //lazily initialize the binding instance for the header view
  private val headerBinding:B by lazy {
    DataBindingUtil.inflate<B>(LayoutInflater.from(root.context),
    headerLayout, null, false)
  }

  override fun onDrawOver(canvas: Canvas, parent: RecyclerView, 
  state: State) {
  super.onDrawOver(canvas, parent, state)
  /* 
    This needs to be customized, please continue reading for the    implementation
  */
  }
}

Above is the basic structure for the custom ItemDecoration. Now we have to understand what customization goes inside the onDrawOver function.
Let's continue customizing this function:

override fun onDrawOver(canvas: Canvas, parent: RecyclerView, sate: State) {
  super.onDrawOver(canvas, parent, state)

  val topChild = parent.getChildAt(0)
  val secondChild = parent.getChildAt(1)

  parent.getChildAdapterPosition(topChild).let { topPosition ->
    val header = adapter.getHeaderForCurrentPosition(topPosition)
    headerView.tvStickyHeader.text = header

    layoutHeaderView(topChild)
    canvas.drawHeaderView(topChild, secondChild)
  }
}

private fun layoutHeaderView(topView: View) {
  headerView.measure(
    MeasureSpec.makeMeasureSpec(topView.width, MeasureSpec.EXACTLY),
    MeasureSpec.makeMeasureSpec(MeasureSpec.UNSPECIFIED, MeasureSpec.UNSPECIFIED)
   )
  headerView.layout(topView.left, 0, topView.right, headerView.measuredHeight)
}

private fun Canvas.drawHeaderView(topView: View, secondChild: View?) {
  save()
  translate(0f, calculateHeaderTop(topView, secondChild)
  headerView.draw(this)
  restore()
}

private fun calculateHeaderTop(topView: View, secondChild: View?) : Float = 
secondChild?.let { second -> 
  // If there is any custom height to be added, calculate here
  if (secondView.findViewById(headerView.id)?.visibility != View.GONE) {
    secondView.top.toFloat()
  } else {
    maxOf(topView.top, 0).toFloat()
  }
} ?: maxOf(topView.top, 0).toFloat()

onDrawOver

In this function,

we get the reference for the first and second item of the RecyclerView
we retrieve the header text for the top child
measure the header
calculate header top and draw the header

adapter.getHeaderForCurrentPosition(topPosition)

This adapter function returns the header text for the given position.
e.g.

// items is the list of objects displayed in the RecyclerView
fun getHeaderForCurrentPosition(position: Int) = if (position in items.indices) {
    items[position]
  } else {
    ""
  }

- layoutHeaderView(topView: View)

This function measures the EXACT width of the header view to be drawn. Note that the height is unspecified as we are using the header view's measuredHeight.

- Canvas.drawHeaderView(topView: View, secondChild: View?)

This function saves the canvas, translates the canvas to the header view's calculated top, draws the header and restores the canvas.

- calculateHeaderTop(topView: View, secondChild: View?)

This function calculates the top of the header. If second view is visible, we take reference of secondView's top, else the header's top is topView's top.

Basic Use

// This custom decoration can be used in a fragment as follows
class SomeFragment() {
  // initialization part...
  fragmentBinding.itemList.addItemDecoration(
      StickyHeaderItemDecoration<ViewStickyHeaderBinding>(
        someAdapter, fragmentBinding.root, R.layout.view_sticky_header
      )
    )

Basic Scroll Behavior

When we initialize the list with the items, the header text for the first item will be displayed as soon as all data is inflated. Then as we scroll through the list, when the top of the second item (plus some threshold is optional) touches the bottom of the sticky header then the header for the second item is drawn. And this continues as we scroll up through the list.
As we scroll down through the list, the reverse behavior occurs and the header text are drawn.
The adapter class is responsible for providing the header text for any given position if the position is within bounds of the items size.

Please provide feedback in the comment section.

Android RecyclerView single choice adapter

Bigyan Thapa — Fri, 06 Dec 2019 03:39:39 +0000

More often than not, we as android developers come across a requirement to display a list of objects and make that list selectable in a single choice mode. Over the time, several ways of implementations have been done. I wanted to share the approach that I took recently to achieve this functionality. This requires basic understanding of kotlin, data binding and a bit of mvvm.

The basic idea here is to keep track of the selected position in the adapter as observable value and right after this changes, call notifyItemChanged() for the oldPosition and the newPosition with will re-bind the user to the views that will in turn reverse the check-mark for the associated RadioButton. When the list item is clicked, it updates the selectedPosition to the position of the clicked list item.

User

    data class User(val name: String, val address: String, val age: Int)

RecyclerView Adapter

    class UserAdapter : RecyclerView.Adapter<UserAdapter.UserViewHolder> {

        var users: List<User> = emptyList()
            set(value) {
                field = value
                notifyDataSetChanged()
            }

       // This keeps track of the currently selected position
       var selectedPosition by Delegates.observable(-1) { property, oldPos, newPos ->
            if (newPos in items.indices) {
                notifyItemChanged(oldPos)
                notifyItemChanged(newPos)
           }
       }

        override fun onCreateViewHolder(parent: ViewGroup, viewType:   Int): UserViewHolder {
            val layoutInflater = LayoutInflater.from(parent.context)
            val viewBinding: ViewListItemBinding =
                        DataBindingUtil.inflate(layoutInflater,R.layout.view_list_item, parent, false)
        return UserViewHolder(viewBinding)
        }

       override fun getItemCount(): Int = users.size

       override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
        if (position in users.indices){
            holder.bind(items[position], position == selectedPosition)
            holder.itemView.setOnClickListener { selectedPosition = position }
        }
    }

    inner class UserViewHolder(private val viewBinding: ViewListItemBinding) :
        RecyclerView.ViewHolder(viewBinding.root) {

        fun bind(user: User, selected: Boolean) {
            with(event) {
                viewBinding.tvUserName.text = name
                viewBinding.tvAddress.text = address
                viewBinding.tvAge.text = "$age"
                viewBinding.btnChecked.isChecked = selected
            }
        }
    }

View List Item

    <?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools">
      <LinearLayout
        android:id="@+id/mainContainer"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:clickable="true"
        android:focusable="true"
        android:foreground="?android:attr/selectableItemBackground"
        android:minHeight="72dp"
        android:orientation="horizontal"
        android:padding="16dp">

        <androidx.appcompat.widget.AppCompatRadioButton
          android:id="@+id/btnChecked"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="start|center_vertical"
          android:layout_marginEnd="@dimen/margin_8dp"
          android:clickable="false"
          tools:checked="true" />

          <LinearLayout
             android:layout_width="0dp"
             android:layout_height="wrap_content"
             android:layout_marginStart="8dp"
             android:layout_weight="1"
             android:orientation="vertical">

             <androidx.appcompat.widget.AppCompatTextView
                android:id="@+id/tvUserName"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                tools:text="User User" />

             <androidx.appcompat.widget.AppCompatTextView
                android:id="@+id/tvAddress"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                tools:text="United States" />

             <androidx.appcompat.widget.AppCompatTextView
                android:id="@+id/tvAge"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                tools:text="26" />
           </LinearLayout>

       </LinearLayout>
   </layout>

User Fragment

   class UserFragment : Fragment() {

     private lateinit binding: FragmentUserBinding
     private lateinit viewModel: UserViewModel
     private val adapter: UserAdapter = UserAdapter()     

     override onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
     super.onCreateView(inflater, container, savedInstanceState)
     binding = DataBindingUtil.inflate(inflater, R.layout.fragment_user, container, false)

     binding.recyclerView.layoutManager = LinearLayoutManager(context)
     binding.recyclerView.adapter = adapter

     return binding.root
     }

     override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        // initialize UserViewModel here ... the viewModel exposes     `users` as LiveData which we observe here and assign to the adapter

        viewModel.users.observe(this, Observer { users ->
            adapter.users = users
        }
     }
   }

The source of data is the ViewModel. The view model fetches the users using some repository in the background thread and exposes that as LiveData. The Fragment can initialize the view model and observe the live data exposed by the view model. When it receives the data, it sets that data to the adapter which then binds that data to the RecyclerView. This is a pretty basic version of the implementation. We can take this approach and expand into multiple dimensions to achieve various different behaviors.

Please provide comments if you have questions or feedback.
Thank you!

Forem: Bigyan Thapa

Gain performance by inline

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