Convert Java files to Kotlin (#328)

* Convert Java files to Kotlin

* Update following @thagikura's comments

Author: MGaetan89

build.gradle

@@ -17,32 +17,37 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
+    ext {
+        minSdkVersion = 9
+        targetSdkVersion = 25
+        compileSdkVersion = 25
+        buildToolsVersion = "25.0.3"
+        androidGradlePluginVersion = "2.3.3"
+        androidMavenGradlePluginVersion = "1.5"
+        gradleBintrayPluginVersion = "1.6"
+        kotlinVersion = "1.1.3"
+        supportLibVersion = "25.3.1"
+        espressoVersion = "2.2.2"
+        testRunnerVersion = "0.5"
+        junitVersion = "4.12"
+    }
+
     repositories {
         jcenter()
         maven {
             url 'https://maven.google.com'
         }
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.3'
-        classpath 'com.github.dcendents:android-maven-gradle-plugin:1.5'
-        classpath 'com.jfrog.bintray.gradle:gradle-bintray-plugin:1.6'
+        classpath "com.android.tools.build:gradle:$androidGradlePluginVersion"
+        classpath "com.github.dcendents:android-maven-gradle-plugin:$androidMavenGradlePluginVersion"
+        classpath "com.jfrog.bintray.gradle:gradle-bintray-plugin:$gradleBintrayPluginVersion"
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
     }
 }
 
-ext {
-    minSdkVersion = 9
-    targetSdkVersion = 25
-    compileSdkVersion = 25
-    buildToolsVersion = "25.0.3"
-    supportLibVersion = "25.3.1"
-    espressoVersion = "2.2.2"
-    testRunnerVersion = "0.5"
-    junitVersion = "4.12"
-}
-
 allprojects {
     repositories {
         jcenter()
@@ -63,9 +68,9 @@ project.ext.preDexLibs = !project.hasProperty('disablePreDex')
 
 subprojects {
     project.plugins.whenPluginAdded { plugin ->
-        if ("com.android.build.gradle.AppPlugin".equals(plugin.class.name)) {
+        if ("com.android.build.gradle.AppPlugin" == plugin.class.name) {
             project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
-        } else if ("com.android.build.gradle.LibraryPlugin".equals(plugin.class.name)) {
+        } else if ("com.android.build.gradle.LibraryPlugin" == plugin.class.name) {
             project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
         }
     }

demo-cat-gallery/build.gradle

@@ -15,6 +15,7 @@
  */
 
 apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
 
 android {
     compileSdkVersion rootProject.ext.compileSdkVersion
@@ -39,8 +40,9 @@ android {
 }
 
 dependencies {
+    compile project(path: ":flexbox")
     compile "com.android.support:appcompat-v7:${rootProject.ext.supportLibVersion}"
     compile "com.android.support:design:${rootProject.ext.supportLibVersion}"
     compile "com.android.support:recyclerview-v7:${rootProject.ext.supportLibVersion}"
-    compile project(path: ":flexbox")
+    compile "org.jetbrains.kotlin:kotlin-stdlib:${rootProject.ext.kotlinVersion}"
 }

demo-cat-gallery/src/main/java/com/google/android/flexbox/apps/catgallery/CatAdapter.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2017 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.flexbox.apps.catgallery
+
+import android.support.v7.widget.RecyclerView
+import android.view.LayoutInflater
+import android.view.ViewGroup
+
+/**
+ * Adapter class that handles the data set with the {@link RecyclerView.LayoutManager}
+ */
+internal class CatAdapter : RecyclerView.Adapter<CatViewHolder>() {
+
+    companion object {
+        private val CAT_IMAGE_IDS = intArrayOf(
+                R.drawable.cat_1,
+                R.drawable.cat_2,
+                R.drawable.cat_3,
+                R.drawable.cat_4,
+                R.drawable.cat_5,
+                R.drawable.cat_6,
+                R.drawable.cat_7,
+                R.drawable.cat_8,
+                R.drawable.cat_9,
+                R.drawable.cat_10,
+                R.drawable.cat_11,
+                R.drawable.cat_12,
+                R.drawable.cat_13,
+                R.drawable.cat_14,
+                R.drawable.cat_15,
+                R.drawable.cat_16,
+                R.drawable.cat_17,
+                R.drawable.cat_18,
+                R.drawable.cat_19
+        )
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CatViewHolder {
+        val view = LayoutInflater.from(parent.context)
+                .inflate(R.layout.viewholder_cat, parent, false)
+        return CatViewHolder(view)
+    }
+
+    override fun onBindViewHolder(holder: CatViewHolder, position: Int) {
+        val pos = position % CAT_IMAGE_IDS.size
+        holder.bindTo(CAT_IMAGE_IDS[pos])
+    }
+
+    override fun getItemCount() = CAT_IMAGE_IDS.size * 4
+}

demo-cat-gallery/src/main/java/com/google/android/flexbox/apps/catgallery/CatAdapter.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2017 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.flexbox.apps.catgallery
+
+import android.support.annotation.DrawableRes
+import android.support.v7.widget.RecyclerView
+import android.view.View
+import android.widget.ImageView
+import com.google.android.flexbox.FlexboxLayoutManager
+
+/**
+ * ViewHolder that represents a cat image.
+ */
+internal class CatViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
+
+    private val imageView = itemView.findViewById(R.id.imageview) as ImageView
+
+    internal fun bindTo(@DrawableRes drawableRes: Int) {
+        imageView.setImageResource(drawableRes)
+        val lp = imageView.layoutParams
+        if (lp is FlexboxLayoutManager.LayoutParams) {
+            lp.flexGrow = 1f
+        }
+    }
+}