Support setting color of activated indicator

indicator-fast-scroll/src/main/java/com/reddit/indicatorfastscroll/FastScrollerView.kt

@@ -46,10 +46,31 @@ class FastScrollerView @JvmOverloads constructor(
   defStyleRes
 ) {
 
-  var iconColor: ColorStateList? by onUpdate(::bindItemIndicatorViews)
-  var textAppearanceRes: Int by onUpdate(::bindItemIndicatorViews)
-  var textColor: ColorStateList? by onUpdate(::bindItemIndicatorViews)
-  var textPadding: Float by onUpdate(::bindItemIndicatorViews)
+  var iconColor: ColorStateList? = null
+    set(value) {
+      field = value
+      pressedIconColor = value?.getColorForState(intArrayOf(android.R.attr.state_activated))
+      bindItemIndicatorViews()
+    }
+  var textAppearanceRes: Int = 0
+    set(value) {
+      field = value
+      bindItemIndicatorViews()
+    }
+  var textColor: ColorStateList? = null
+    set(value) {
+      field = value
+      pressedTextColor = value?.getColorForState(intArrayOf(android.R.attr.state_activated))
+      bindItemIndicatorViews()
+    }
+  var textPadding: Float = 0f
+    set(value) {
+      field = value
+      bindItemIndicatorViews()
+    }
+
+  private var pressedIconColor: Int? = null
+  private var pressedTextColor: Int? = null
 
   internal var itemIndicatorsBuilder: ItemIndicatorsBuilder = ItemIndicatorsBuilder()
 
@@ -79,7 +100,7 @@ class FastScrollerView @JvmOverloads constructor(
    * The function will be called when building the list of indicators, which happens after the
    * RecyclerView's adapter's data changes. It will be called on the UI thread.
    */
-  var showIndicator: ((FastScrollItemIndicator, Int, Int) -> Boolean)? by onUpdate {
+  var showIndicator: ((FastScrollItemIndicator, Int, Int) -> Boolean)? by onUpdate { _ ->
     postUpdateItemIndicators()
   }
 
@@ -235,7 +256,7 @@ class FastScrollerView @JvmOverloads constructor(
       }
 
     // Optimize the views by batching adjacent text indicators into a single TextView
-    val viewCreators = ArrayList<() -> View>()
+    val views = ArrayList<View>()
     itemIndicators.run {
       var index = 0
       while (index <= lastIndex) {
@@ -244,12 +265,12 @@ class FastScrollerView @JvmOverloads constructor(
           .takeWhile { it is FastScrollItemIndicator.Text }
           as List<FastScrollItemIndicator.Text>
         if (textIndicatorsBatch.isNotEmpty()) {
-          viewCreators.add { createTextView(textIndicatorsBatch) }
+          views.add(createTextView(textIndicatorsBatch))
           index += textIndicatorsBatch.size
         } else {
           when (val indicator = this[index]) {
             is FastScrollItemIndicator.Icon -> {
-              viewCreators.add { createIconView(indicator) }
+              views.add(createIconView(indicator))
             }
             is FastScrollItemIndicator.Text -> {
               throw IllegalStateException("Text indicator wasn't batched")
@@ -259,19 +280,20 @@ class FastScrollerView @JvmOverloads constructor(
         }
       }
     }
-    viewCreators.forEach { createView ->
-      addView(createView())
-    }
+    views.forEach(::addView)
   }
 
   private fun selectItemIndicator(
     indicator: FastScrollItemIndicator,
-    indicatorCenterY: Int
+    indicatorCenterY: Int,
+    touchedView: View,
+    textLine: Int?
   ) {
     val position = itemIndicatorsWithPositions
       .first { it.first == indicator }
       .let(ItemIndicatorWithPosition::second)
     if (position != lastSelectedPosition) {
+      clearSelectedItemIndicator()
       lastSelectedPosition = position
       if (useDefaultScroller) {
         scrollToPosition(position)
@@ -284,12 +306,29 @@ class FastScrollerView @JvmOverloads constructor(
           HapticFeedbackConstants.KEYBOARD_TAP
         }
       )
+      if (touchedView is ImageView) {
+        touchedView.isActivated = true
+      } else if (textLine != null) {
+        pressedTextColor?.let { color ->
+          TextColorUtil.highlightAtIndex(touchedView as TextView, textLine, color)
+        }
+      }
       itemIndicatorSelectedCallbacks.forEach {
         it.onItemIndicatorSelected(indicator, indicatorCenterY, position)
       }
     }
   }
 
+  private fun clearSelectedItemIndicator() {
+    lastSelectedPosition = null
+    if (pressedIconColor != null) {
+      children.filterIsInstance<ImageView>().forEach { it.isActivated = false }
+    }
+    if (pressedTextColor != null) {
+      children.filterIsInstance<TextView>().forEach(TextColorUtil::clearHighlight)
+    }
+  }
+
   private fun scrollToPosition(position: Int) {
     recyclerView!!.apply {
       stopScroll()
@@ -301,9 +340,9 @@ class FastScrollerView @JvmOverloads constructor(
   override fun onTouchEvent(event: MotionEvent): Boolean {
     fun View.containsY(y: Int) = y in (top until bottom)
 
-    if (event.action in MOTIONEVENT_STOP_ACTIONS) {
+    if (event.actionMasked in MOTIONEVENT_STOP_ACTIONS) {
       isPressed = false
-      lastSelectedPosition = null
+      clearSelectedItemIndicator()
       onItemIndicatorTouched?.invoke(false)
       return false
     }
@@ -316,7 +355,7 @@ class FastScrollerView @JvmOverloads constructor(
           is ImageView -> {
             val touchedIndicator = view.tag as FastScrollItemIndicator.Icon
             val centerY = view.y.toInt() + (view.height / 2)
-            selectItemIndicator(touchedIndicator, centerY)
+            selectItemIndicator(touchedIndicator, centerY, view, textLine = null)
             consumed = true
           }
           is TextView -> {
@@ -332,7 +371,7 @@ class FastScrollerView @JvmOverloads constructor(
 
             val centerY = view.y.toInt() +
               (textLineHeight / 2) + (touchedIndicatorIndex * textLineHeight)
-            selectItemIndicator(touchedIndicator, centerY)
+            selectItemIndicator(touchedIndicator, centerY, view, textLine = touchedIndicatorIndex)
             consumed = true
           }
         }

indicator-fast-scroll/src/main/java/com/reddit/indicatorfastscroll/ResourcesUtil.kt

@@ -1,6 +1,8 @@
 package com.reddit.indicatorfastscroll
 
+import android.content.res.ColorStateList
 import android.view.View
+import androidx.annotation.ColorInt
 import androidx.annotation.StyleRes
 
 internal fun View.throwIfMissingAttrs(@StyleRes styleRes: Int, block: () -> Unit) {
@@ -15,3 +17,8 @@ internal fun View.throwIfMissingAttrs(@StyleRes styleRes: Int, block: () -> Unit
     )
   }
 }
+
+@ColorInt
+internal fun ColorStateList.getColorForState(stateSet: IntArray): Int? {
+  return getColorForState(stateSet, defaultColor).takeIf { it != defaultColor }
+}

indicator-fast-scroll/src/main/java/com/reddit/indicatorfastscroll/TextColorUtil.kt

@@ -0,0 +1,42 @@
+package com.reddit.indicatorfastscroll
+
+import android.text.SpannableString
+import android.text.Spanned
+import android.text.style.ForegroundColorSpan
+import android.widget.TextView
+import androidx.core.text.clearSpans
+
+internal object TextColorUtil {
+
+  fun highlightAtIndex(textView: TextView, highlightedIndex: Int?, color: Int) {
+    textView.apply {
+      if (highlightedIndex == null) {
+        clearHighlight(this)
+      } else {
+        text = SpannableString.valueOf(text).apply {
+          clearSpans()
+          val linesUpToHighlight = lineSequence().take(highlightedIndex + 1).toList() // inclusive
+          val start = linesUpToHighlight
+            .dropLast(1)
+            .fold(0) { acc, line ->
+              acc + line.length + 1
+            }
+          val highlightedLineSize = linesUpToHighlight.lastOrNull()?.length ?: 0
+
+          setSpan(ForegroundColorSpan(color), start, start + highlightedLineSize, 0)
+        }
+      }
+    }
+  }
+
+  fun clearHighlight(textView: TextView) {
+    textView.apply {
+      if (text is Spanned) {
+        text = SpannableString.valueOf(text).apply {
+          clearSpans()
+        }
+      }
+    }
+  }
+
+}

indicator-fast-scroll/src/main/java/com/reddit/indicatorfastscroll/UpdateDelegate.kt

@@ -3,7 +3,7 @@ package com.reddit.indicatorfastscroll
 import kotlin.properties.ReadWriteProperty
 import kotlin.reflect.KProperty
 
-internal class UpdateDelegate<T>(val update: () -> Unit) : ReadWriteProperty<Any?, T> {
+internal class UpdateDelegate<T>(val update: (T) -> Unit) : ReadWriteProperty<Any?, T> {
 
   var set = false
   var value: T? = null
@@ -21,12 +21,14 @@ internal class UpdateDelegate<T>(val update: () -> Unit) : ReadWriteProperty<Any
     this.set = true
     this.value = value
     if (wasSet) {
-      update()
+      update(value)
     }
   }
 }
 
 /**
  * A delegate that sets a backing value and calls [update] on every change after the first.
  */
-internal fun <T> onUpdate(update: () -> Unit) = UpdateDelegate<T>(update)
+internal fun <T> onUpdate(update: (T) -> Unit) = UpdateDelegate(update)
+
+internal fun <T> onUpdate(update: () -> Unit) = UpdateDelegate<T> { update() }

sample/src/main/res/color/pressed_selector.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
+  <item android:color="@color/colorAccent" android:state_activated="true" />
   <item android:color="@color/colorPrimary" android:state_pressed="true" />
   <item android:color="@android:color/black" />
 </selector>