Carousel building with Kotlin DSL - Step 1 (#967)

* apply commit eeff265

* fix wrong merge

* Move the builder in sample app waiting for a more robust api

* Actually let's do it for the carousel no snap

* Use new DSL in sample app

* ktlint

* ktlint

* Simplify, BaseEpoxyController class -> ModelCollector interface

* ktlint

Co-authored-by: Eli Hart <eli.hart@airbnb.com>
Co-authored-by: Emmanuel Boudrant <eboudrant@netflix.com>

epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyController.java

@@ -44,7 +44,7 @@
  * treated as immutable and never modified again. This is necessary for adapter updates to be
  * accurate.
  */
-public abstract class EpoxyController implements StickyHeaderCallbacks {
+public abstract class EpoxyController implements ModelCollector, StickyHeaderCallbacks {
 
   /**
    * We check that the adapter is not connected to multiple recyclerviews, but when a fragment has
@@ -127,8 +127,8 @@ public EpoxyController(Handler modelBuildingHandler, Handler diffingHandler) {
 
   @Retention(RetentionPolicy.SOURCE)
   @IntDef({RequestedModelBuildType.NONE,
-           RequestedModelBuildType.NEXT_FRAME,
-           RequestedModelBuildType.DELAYED})
+      RequestedModelBuildType.NEXT_FRAME,
+      RequestedModelBuildType.DELAYED})
   private @interface RequestedModelBuildType {
     int NONE = 0;
     /** A request has been made to build models immediately. It is posted. */
@@ -463,7 +463,7 @@ private void assertNotBuildingModels() {
    * Add the model to this controller. Can only be called from inside {@link
    * EpoxyController#buildModels()}.
    */
-  protected void add(@NonNull EpoxyModel<?> model) {
+  public void add(@NonNull EpoxyModel<?> model) {
     model.addTo(this);
   }
 
@@ -475,7 +475,7 @@ protected void add(@NonNull EpoxyModel<?>... modelsToAdd) {
     modelsBeingBuilt.ensureCapacity(modelsBeingBuilt.size() + modelsToAdd.length);
 
     for (EpoxyModel<?> model : modelsToAdd) {
-      model.addTo(this);
+      add(model);
     }
   }
 
@@ -487,7 +487,7 @@ protected void add(@NonNull List<? extends EpoxyModel<?>> modelsToAdd) {
     modelsBeingBuilt.ensureCapacity(modelsBeingBuilt.size() + modelsToAdd.size());
 
     for (EpoxyModel<?> model : modelsToAdd) {
-      model.addTo(this);
+      add(model);
     }
   }
 

epoxy-adapter/src/main/java/com/airbnb/epoxy/ModelCollector.kt

@@ -0,0 +1,10 @@
+package com.airbnb.epoxy
+
+/**
+ * Interface used to collect models. Used by [EpoxyController]. It is also convenient to build DSL
+ * helpers for carousel: @link https://github.com/airbnb/epoxy/issues/847.
+ */
+interface ModelCollector {
+
+    fun add(model: EpoxyModel<*>)
+}

epoxy-processor/src/main/java/com/airbnb/epoxy/ClassNames.kt

@@ -55,6 +55,8 @@ object ClassNames {
     @JvmField
     val EPOXY_CONTROLLER = get(PKG_EPOXY, "EpoxyController")!!
     @JvmField
+    val MODEL_COLLECTOR = get(PKG_EPOXY, "ModelCollector")!!
+    @JvmField
     val EPOXY_STYLE_BUILDER_CALLBACK = get(PKG_EPOXY, "StyleBuilderCallback")!!
     @JvmField
     val EPOXY_CONTROLLER_HELPER = get(PKG_EPOXY, "ControllerHelper")!!

epoxy-processor/src/main/java/com/airbnb/epoxy/KotlinModelBuilderExtensionWriter.kt

@@ -95,7 +95,7 @@ internal class KotlinModelBuilderExtensionWriter(
         )
 
         FunSpec.builder(getMethodName(model)).run {
-            receiver(ClassNames.EPOXY_CONTROLLER.toKPoet())
+            receiver(ClassNames.MODEL_COLLECTOR.toKPoet())
             val params = constructor?.params ?: listOf()
             addParameters(params.toKParams())
 
@@ -117,13 +117,14 @@ internal class KotlinModelBuilderExtensionWriter(
             addModifiers(KModifier.INLINE)
             if (constructorIsNotPublic) addModifiers(KModifier.INTERNAL)
 
+            addStatement("add(")
             beginControlFlow(
                 "$tick%T$tick(${params.joinToString(", ") { it.name }}).apply",
                 modelClass
             )
             addStatement("modelInitializer()")
             endControlFlow()
-            addStatement(".addTo(this)")
+            addStatement(")")
             return build()
         }
     }

kotlinsample/src/main/java/com/airbnb/epoxy/kotlinsample/MainActivity.kt

@@ -8,13 +8,13 @@ import android.widget.Toast
 import androidx.appcompat.app.AppCompatActivity
 import com.airbnb.epoxy.EpoxyRecyclerView
 import com.airbnb.epoxy.EpoxyVisibilityTracker
-import com.airbnb.epoxy.kotlinsample.models.CarouselItemCustomViewModel_
+import com.airbnb.epoxy.kotlinsample.helpers.carouselNoSnapBuilder
 import com.airbnb.epoxy.kotlinsample.models.ItemDataClass
 import com.airbnb.epoxy.kotlinsample.models.ItemViewBindingDataClass
+import com.airbnb.epoxy.kotlinsample.models.carouselItemCustomView
 import com.airbnb.epoxy.kotlinsample.models.itemCustomView
 import com.airbnb.epoxy.kotlinsample.models.itemEpoxyHolder
 import com.airbnb.epoxy.kotlinsample.models.itemViewBindingEpoxyHolder
-import com.airbnb.epoxy.kotlinsample.views.carouselNoSnap
 
 class MainActivity : AppCompatActivity() {
     private lateinit var recyclerView: EpoxyRecyclerView
@@ -71,18 +71,15 @@ class MainActivity : AppCompatActivity() {
                     }
                 }
 
-                carouselNoSnap {
+                carouselNoSnapBuilder {
                     id("carousel $i")
-                    models(mutableListOf<CarouselItemCustomViewModel_>().apply {
-                        val lastPage = 10
-                        for (j in 0 until lastPage) {
-                            add(
-                                CarouselItemCustomViewModel_()
-                                    .id("carousel $i-$j")
-                                    .title("Page $j / $lastPage")
-                            )
+                    val lastPage = 10
+                    for (j in 0 until lastPage) {
+                        carouselItemCustomView {
+                            id("carousel $i-$j")
+                            title("Page $j / $lastPage")
                         }
-                    })
+                    }
                 }
 
                 // Since data classes do not use code generation, there's no extension generated here

kotlinsample/src/main/java/com/airbnb/epoxy/kotlinsample/helpers/EpoxyCarouselNoSnapBuilder.kt

@@ -0,0 +1,41 @@
+package com.airbnb.epoxy.kotlinsample.helpers
+
+import com.airbnb.epoxy.EpoxyModel
+import com.airbnb.epoxy.ModelCollector
+import com.airbnb.epoxy.kotlinsample.views.CarouselNoSnapModelBuilder
+import com.airbnb.epoxy.kotlinsample.views.CarouselNoSnapModel_
+
+/**
+ * Example that illustrate how to add a builder for nested list (ex: carousel) that allow building
+ * it using DSL :
+ *
+ *   carouselBuilder {
+ *     id(...)
+ *     for (...) {
+ *       carouselItemCustomView {
+ *         id(...)
+ *       }
+ *     }
+ *   }
+ *
+ * @link https://github.com/airbnb/epoxy/issues/847
+ */
+fun ModelCollector.carouselNoSnapBuilder(builder: EpoxyCarouselNoSnapBuilder.() -> Unit): CarouselNoSnapModel_ {
+    val carouselBuilder = EpoxyCarouselNoSnapBuilder().apply { builder() }
+    add(carouselBuilder.carouselNoSnapModel)
+    return carouselBuilder.carouselNoSnapModel
+}
+
+class EpoxyCarouselNoSnapBuilder(
+    internal val carouselNoSnapModel: CarouselNoSnapModel_ = CarouselNoSnapModel_()
+) : ModelCollector, CarouselNoSnapModelBuilder by carouselNoSnapModel {
+    private val models = mutableListOf<EpoxyModel<*>>()
+
+    override fun add(model: EpoxyModel<*>) {
+        models.add(model)
+
+        // Set models list every time a model is added so that it can run debug validations to
+        // ensure it is still valid to mutate the carousel model.
+        carouselNoSnapModel.models(models)
+    }
+}