Add padding methods by percentage of the screen width and dp

Author: hendrawd

README.md

@@ -25,9 +25,20 @@ then you just need to set deck default padding
 private val deckPager by lazy { activity.findViewById<Deck>(R.id.deck_pager) }
 
 private fun initDeck() {
-    deckPager.useDefaultPadding(activity)
+    deckPager.setDefaultPadding(activity)
 }
+```
+
+or set padding based on percentage of the screen width
 
+```kotlin
+deckPager.setPercentagePadding(activity)
+```
+
+or set padding based on dp value
+
+```kotlin
+deckPager.setDpPadding(activity)
 ```
 
 ##### Remember you can set all other view pager properties with deck

app/src/main/java/com/example/bloder/deck/DeckAdapter.kt

@@ -1,6 +1,7 @@
 package com.example.bloder.deck
 
 import android.content.Context
+import android.support.v4.content.ContextCompat
 import android.support.v4.view.PagerAdapter
 import android.support.v7.widget.CardView
 import android.view.LayoutInflater
@@ -18,7 +19,8 @@ class DeckAdapter(private val context: Context) : PagerAdapter() {
     override fun instantiateItem(container: ViewGroup?, position: Int): Any {
         val view = LayoutInflater.from(context).inflate(R.layout.card, null)
         container?.addView(view, 0)
-        view.findViewById<CardView>(R.id.card).cardBackgroundColor = context.getColorStateList(cards[position].color)
+        view.findViewById<CardView>(R.id.card).cardBackgroundColor =
+                ContextCompat.getColorStateList(context, cards[position].color)
         view.findViewById<TextView>(R.id.title).text = cards[position].name
         return view
     }

app/src/main/java/com/example/bloder/deck/MainActivity.kt

@@ -16,6 +16,6 @@ class MainActivity : AppCompatActivity() {
         setContentView(R.layout.activity_main)
         deckPager.offscreenPageLimit = 5
         deckPager.adapter = DeckAdapter(this)
-        deckPager.useDefaultPadding(this)
+        deckPager.setDefaultPadding(this)
     }
 }

lib/src/main/java/com/example/lib/CoverFlowTransformer.kt

@@ -7,17 +7,18 @@ import android.view.View
 /**
  * Created by bloder on 25/08/17.
  */
+private const val SCALE_MIN = .3f
+private const val SCALE_MAX = 1f
+private const val MIN_ALPHA = .5f
+private const val SCALE = .05f
+
 class CoverFlowTransformer : ViewPager.PageTransformer {
 
-    private var SCALE_MIN = 0.3f
-    private var SCALE_MAX = 1f
-    private var MIN_ALPHA = 0.5f
-    private var scale = .05f
-    private var paddingFactor: Float = 0.08f
+    var paddingFactor: Float = 0.08f
 
     override fun transformPage(page: View, position: Float) {
         val realPosition = position - paddingFactor
-        val realScale = getFloat(1 - Math.abs(realPosition * scale), SCALE_MIN, SCALE_MAX)
+        val realScale = getFloat(1 - Math.abs(realPosition * SCALE), SCALE_MIN, SCALE_MAX)
         page.scaleX = realScale
         page.scaleY = realScale
         if (realPosition != 0f) {

lib/src/main/java/com/example/lib/Deck.kt

@@ -5,25 +5,73 @@ import android.content.Context
 import android.support.v4.view.ViewPager
 import android.util.AttributeSet
 import android.util.DisplayMetrics
+import android.util.TypedValue
 
 /**
  * Created by bloder on 25/08/17.
  */
+private const val DEFAULT_PERCENTAGE_PADDING = 8
+
 class Deck : ViewPager {
 
+    private val pageTransformer = CoverFlowTransformer()
+
     constructor(context: Context) : super(context)
     constructor(context: Context, attributeSet: AttributeSet) : super(context, attributeSet)
 
-    init { initView() }
+    init {
+        initView()
+    }
+
+    private fun initView() {
+        setPageTransformer(true, pageTransformer)
+    }
 
-    private fun initView() = this.setPageTransformer(true, CoverFlowTransformer())
+    /**
+     * Set left and right padding with default value
+     */
+    fun setDefaultPadding(context: Activity) {
+        setPercentagePadding(context, DEFAULT_PERCENTAGE_PADDING)
+    }
 
-    fun useDefaultPadding(context: Activity) {
-        val metrics = DisplayMetrics()
-        context.windowManager.defaultDisplay.getMetrics(metrics)
-        val padding = (metrics.widthPixels * 0.08).toInt()
-        setPadding(padding, 0, padding, 0)
+    /**
+     * Set left and right padding based on percentage of the screen width
+     * If the percentage is more than 18, the left and right items height might not be consistent
+     */
+    fun setPercentagePadding(context: Activity, percentage: Int) {
+        when {
+            percentage == 0 -> initProperties(context, 0f)
+            percentage < 0 -> throw IllegalArgumentException("Percentage can't be lower than 0")
+            percentage > 100 -> throw IllegalArgumentException("Percentage can't be higher than 100")
+            else -> {
+                val metrics = DisplayMetrics()
+                context.windowManager.defaultDisplay.getMetrics(metrics)
+                val padding = metrics.widthPixels * percentage / 100f
+                initProperties(context, padding)
+            }
+        }
+    }
+
+    /**
+     * Set left and right padding based on dp value
+     */
+    fun setDpPadding(context: Activity, dp: Float) {
+        val padding = TypedValue.applyDimension(
+                TypedValue.COMPLEX_UNIT_DIP,
+                dp,
+                context.resources.displayMetrics
+        )
+        initProperties(context, padding)
+    }
+
+    private fun initProperties(context: Activity, padding: Float) {
+        val intPadding = padding.toInt()
+        setPadding(intPadding, 0, intPadding, 0)
         clipToPadding = false
         pageMargin = 0
+
+        val metrics = DisplayMetrics()
+        context.windowManager.defaultDisplay.getMetrics(metrics)
+        pageTransformer.paddingFactor = padding / metrics.widthPixels
     }
 }