add crossfade view

views/src/main/java/ru/touchin/roboswag/views/CrossfadeView.kt

@@ -0,0 +1,44 @@
+package ru.touchin.roboswag.views
+
+import android.content.Context
+import android.util.AttributeSet
+import android.view.View
+import android.view.ViewGroup
+import android.widget.ViewAnimator
+import androidx.annotation.IdRes
+import androidx.core.content.withStyledAttributes
+import androidx.core.view.children
+
+class CrossfadeView @JvmOverloads constructor(
+        context: Context,
+        attrs: AttributeSet? = null
+) : ViewAnimator(context, attrs) {
+
+    @IdRes
+    private var defaultChild: Int = 0
+
+    init {
+        setInAnimation(context, R.anim.fade_in_animation)
+        setOutAnimation(context, R.anim.fade_out_animation)
+
+        context.withStyledAttributes(attrs, R.styleable.CrossfadeView, 0) {
+            defaultChild = getResourceId(R.styleable.CrossfadeView_defaultChild, 0)
+        }
+    }
+
+    fun showChild(@IdRes childId: Int) {
+        children.forEachIndexed { index, view ->
+            if (view.id == childId && displayedChild != index) {
+                displayedChild = index
+            }
+        }
+    }
+
+    override fun addView(child: View, index: Int, params: ViewGroup.LayoutParams?) {
+        super.addView(child, index, params)
+        if (child.id == defaultChild) {
+            showChild(defaultChild)
+        }
+    }
+
+}

views/src/main/res/anim/fade_in_animation.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<alpha
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:duration="300"
+    android:fromAlpha="0.0"
+    android:toAlpha="1.0"/>

views/src/main/res/anim/fade_out_animation.xml

@@ -0,0 +1,5 @@
+<alpha
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:duration="300"
+    android:fromAlpha="1.0"
+    android:toAlpha="0.0"/>

views/src/main/res/values/attrs.xml

@@ -56,4 +56,8 @@
         <attr name="isUnderlineText" format="boolean"/>
     </declare-styleable>
 
+    <declare-styleable name="CrossfadeView">
+        <attr name="defaultChild" format="reference"/>
+    </declare-styleable>
+
 </resources>