Added an animation to the viewpager.

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Fixed #142.
 
+- Added an animation to the viewpager.
+
 - Changed versions handling.
 
 **1.5.4.22**

app/src/main/java/apps/amine/bou/readerforselfoss/ReaderActivity.kt

@@ -6,6 +6,7 @@ import android.support.v4.app.FragmentStatePagerAdapter
 import android.support.v7.app.AppCompatActivity
 import apps.amine.bou.readerforselfoss.api.selfoss.Item
 import apps.amine.bou.readerforselfoss.fragments.ArticleFragment
+import apps.amine.bou.readerforselfoss.transformers.DepthPageTransformer
 import com.ftinc.scoop.Scoop
 import kotlinx.android.synthetic.main.activity_reader.*
 import me.relex.circleindicator.CircleIndicator
@@ -26,6 +27,7 @@ class ReaderActivity : AppCompatActivity() {
         pager.adapter = adapter
         pager.currentItem = currentItem
 
+        pager.setPageTransformer(true, DepthPageTransformer())
         (indicator as CircleIndicator).setViewPager(pager)
     }
 

app/src/main/java/apps/amine/bou/readerforselfoss/transformers/DepthPageTransformer.kt

@@ -0,0 +1,43 @@
+package apps.amine.bou.readerforselfoss.transformers
+
+import android.support.v4.view.ViewPager
+import android.view.View
+
+class DepthPageTransformer : ViewPager.PageTransformer {
+
+    override fun transformPage(view: View, position: Float) {
+        val pageWidth = view.width
+
+        when {
+            position < -1 -> // [-Infinity,-1)
+                // This page is way off-screen to the left.
+                view.alpha = 0F
+            position <= 0 -> { // [-1,0]
+                // Use the default slide transition when moving to the left page
+                view.alpha = 1F
+                view.translationX = 0F
+                view.scaleX = 1F
+                view.scaleY = 1F
+            }
+            position <= 1 -> { // (0,1]
+                // Fade the page out.
+                view.alpha = 1 - position
+
+                // Counteract the default slide transition
+                view.translationX = pageWidth * -position
+
+                // Scale the page down (between MIN_SCALE and 1)
+                val scaleFactor = MIN_SCALE + (1 - MIN_SCALE) * (1 - Math.abs(position))
+                view.scaleX = scaleFactor
+                view.scaleY = scaleFactor
+            }
+            else -> // (1,+Infinity]
+                // This page is way off-screen to the right.
+                view.alpha = 0F
+        }
+    }
+
+    companion object {
+        private val MIN_SCALE = 0.75f
+    }
+}