UseItemdecorationOffsets

Draw Item Separators

DividerItemDecoration

class DividerItemDecoration(color: Int, private val heightInPixels: Int) : RecyclerView.ItemDecoration() {

    private val paint = Paint()

    init {
        paint.color = color
        paint.isAntiAlias = true
    }

    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        super.onDraw(c, parent, state)
        val left = parent.paddingLeft
        val right = parent.width - parent.paddingRight
        val childCount = parent.childCount
        for (i in 0 until childCount) {
            val child = parent.getChildAt(i)
            val params = child.layoutParams as RecyclerView.LayoutParams
            val top = child.bottom + params.bottomMargin
            val bottom = top + heightInPixels
            c.drawRect(left.toFloat(), top.toFloat(), right.toFloat(), bottom.toFloat(), paint)
        }
    }
}

---

Challenge: Draw a Grid

FavoritesFragment

  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    favoritesRecyclerView.layoutManager = LinearLayoutManager(activity)
    favoritesRecyclerView.adapter = adapter
    val heightInPixels = resources.getDimensionPixelSize(R.dimen.list_item_divider_height)
    context?.let {
      favoritesRecyclerView.addItemDecoration(
        DividerItemDecoration(
          ContextCompat.getColor(it, R.color.black), heightInPixels))
    }
  }

CreatureActivity

  private fun setupFoods(){
  foodRecyclerView.layoutManager = GridLayoutManager(this, 3, LinearLayoutManager.VERTICAL, false)
  foodRecyclerView.adapter = adapter
  val foods = CreatureStore.getCreatureFoods(creature)
  adapter.updateFoods(foods)
  val dividerWidthInPixels = resources.getDimensionPixelSize(R.dimen.list_item_divider_height)
  foodRecyclerView.addItemDecoration(
    FoodItemDecoration(
      ContextCompat.getColor(this, R.color.black), dividerWidthInPixels
    ))
}

class FoodItemDecoration(color: Int, private val dividerWidthInPixels: Int) : RecyclerView.ItemDecoration() {

  private val paint = Paint()

  init {
      paint.color = color
      paint.isAntiAlias = true
  }

  override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
      super.onDraw(c, parent, state)

      val childCount = parent.childCount
      for (i in 0 until childCount) {
          val child = parent.getChildAt(i)
          val params = child.layoutParams as RecyclerView.LayoutParams

          var left = parent.paddingLeft
          var right = parent.width - parent.paddingRight
          var top = child.top + params.topMargin
          var bottom = top + dividerWidthInPixels
          c.drawRect(left.toFloat(), top.toFloat(), right.toFloat(), bottom.toFloat(), paint)

          left = child.right - params.rightMargin
          right = left + dividerWidthInPixels
          top = parent.paddingTop
          bottom = parent.height - parent.paddingBottom

          c.drawRect(left.toFloat(), top.toFloat(), right.toFloat(), bottom.toFloat(), paint)
      }
  }
}

---

Animate Items

slide_from_bottom.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate
        android:duration="@android:integer/config_mediumAnimTime"
        android:fromYDelta="50%p"
        android:toYDelta="0" />

    <alpha
        android:duration="@android:integer/config_mediumAnimTime"
        android:fromAlpha="0.0"
        android:toAlpha="1.0"/>
</set>

slide_from_top.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate
        android:duration="@android:integer/config_mediumAnimTime"
        android:fromYDelta="-50%p"
        android:toYDelta="0" />

    <alpha
        android:duration="@android:integer/config_mediumAnimTime"
        android:fromAlpha="0.0"
        android:toAlpha="1.0"/>
</set>

class CreatureCardAdapter(private val creatures: MutableList<Creature>): RecyclerView.Adapter<CreatureCardAdapter.ViewHolder>() {

    enum class ScrollDirection {
        UP, DOWN
    }
    var scrollDirection = ScrollDirection.DOWN

    inner class ViewHolder(itemView: View) : View.OnClickListener, RecyclerView.ViewHolder(itemView) {
    
    // 中略
    }
    
    fun bind(creature: Creature) {
            this.creature = creature
            val context = itemView.context
            val imageResource = context.resources.getIdentifier(creature.uri, null, context.packageName)
            itemView.creatureImage.setImageResource(imageResource)
            itemView.fullName.text = creature.fullName
            setBackgroundColors(context, imageResource)
            animateView(itemView)
    }
    
    private fun animateView(viewToAnimate: View) {
            val animId = if (scrollDirection == ScrollDirection.DOWN) R.anim.slide_from_bottom else R.anim.slide_from_top
            if (viewToAnimate.animation == null) {
                val animation = AnimationUtils.loadAnimation(viewToAnimate.context, animId)
                viewToAnimate.animation = animation
            }
        }
       

AllFragment

    creatureRecyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
      override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
        super.onScrolled(recyclerView, dx, dy)
        adapter.scrollDirection = if (dy > 0) {
          CreatureCardAdapter.ScrollDirection.DOWN
        } else {
          CreatureCardAdapter.ScrollDirection.UP
        }
      }
    })