Added animation when expanding/collapsing login options

app/src/main/java/chat/rocket/android/authentication/loginoptions/ui/LoginOptionsFragment.kt

 package chat.rocket.android.authentication.loginoptions.ui
 
+import android.animation.Animator
+import android.animation.AnimatorListenerAdapter
+import android.animation.ValueAnimator
 import android.app.Activity
 import android.content.Intent
 import android.graphics.PorterDuff
@@ -7,10 +10,13 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.view.animation.AlphaAnimation
+import android.view.animation.Animation
 import android.widget.Button
 import android.widget.LinearLayout
 import androidx.appcompat.view.ContextThemeWrapper
 import androidx.core.view.isVisible
+import androidx.core.view.marginTop
 import androidx.fragment.app.Fragment
 import chat.rocket.android.R
 import chat.rocket.android.analytics.AnalyticsManager
@@ -532,17 +538,80 @@ class LoginOptionsFragment : Fragment(), LoginOptionsView {
     }
 
     private fun expandAccountsView() {
-        (0..accounts_container.childCount)
-            .mapNotNull { accounts_container.getChildAt(it) as? Button }
-            .filter { it.isClickable && !it.isVisible }
-            .forEach { it.isVisible = true }
+        val collapsedHeight = accounts_container.height
+        var expandedHeight = collapsedHeight
+        val optionHeight = accounts_container.getChildAt(1).height +
+                accounts_container.getChildAt(1).marginTop
+        for (i in 0 until accounts_container.childCount) {
+            val bt = accounts_container.getChildAt(i) as Button
+            if (bt.isClickable && !bt.isVisible) {
+                expandedHeight += optionHeight
+            }
+        }
+        val animation = ValueAnimator.ofInt(collapsedHeight, expandedHeight)
+        animation.addUpdateListener {
+            val params = accounts_container.layoutParams
+            params.height = animation.animatedValue as Int
+            accounts_container.layoutParams = params
+        }
+        animation.addListener(object : AnimatorListenerAdapter() {
+            override fun onAnimationStart(animator: Animator) {
+                for (i in 0 until accounts_container.childCount) {
+                    val bt = accounts_container.getChildAt(i) as Button
+                    if (!bt.isVisible) {
+                        bt.isVisible = true
+                        val anim = AlphaAnimation(0.0f, 1.0f)
+                        anim.duration = 400
+                        bt.startAnimation(anim)
+                    }
+                }
+            }
+        })
+        animation.setDuration(400).start()
     }
 
     private fun collapseAccountsView() {
-        (0..accounts_container.childCount)
-            .mapNotNull { accounts_container.getChildAt(it) as? Button }
-            .filter { it.isClickable && it.isVisible }
-            .drop(3)
-            .forEach { it.isVisible = false }
+        val expandedHeight = accounts_container.height
+        var collapsedHeight = expandedHeight
+        val optionHeight = accounts_container.getChildAt(1).height +
+                accounts_container.getChildAt(1).marginTop
+        for (i in 3 until accounts_container.childCount) {
+            val bt = accounts_container.getChildAt(i) as Button
+            if (bt.isClickable && bt.isVisible) {
+                collapsedHeight -= optionHeight
+            }
+        }
+        val animation = ValueAnimator.ofInt(expandedHeight, collapsedHeight)
+        animation.addUpdateListener {
+            val params = accounts_container.layoutParams
+            params.height = animation.animatedValue as Int
+            accounts_container.layoutParams = params
+        }
+        animation.addListener(object : AnimatorListenerAdapter() {
+            override fun onAnimationStart(animator: Animator) {
+                for (i in 3 until accounts_container.childCount) {
+                    val bt = accounts_container.getChildAt(i) as Button
+                    if (bt.isVisible) {
+                        val anim = AlphaAnimation(1.0f, 0.0f)
+                        anim.duration = 400
+                        anim.setAnimationListener(object : Animation.AnimationListener {
+                            override fun onAnimationStart(animation: Animation) {
+
+                            }
+
+                            override fun onAnimationEnd(animation: Animation) {
+                                bt.isVisible = false
+                            }
+
+                            override fun onAnimationRepeat(animation: Animation) {
+
+                            }
+                        })
+                        bt.startAnimation(anim)
+                    }
+                }
+            }
+        })
+        animation.setDuration(400).start()
     }
 }