Merge pull request #158 from Jkly/unable-to-create-component-error

Throw an appropriate exception if createComponent fails

ashley/src/main/kotlin/ktx/ashley/engines.kt

@@ -3,6 +3,7 @@ package ktx.ashley
 import com.badlogic.ashley.core.Component
 import com.badlogic.ashley.core.Engine
 import com.badlogic.ashley.core.Entity
+import kotlin.reflect.KClass
 
 /**
  * An [Entity] created by the provided [Engine].
@@ -23,6 +24,7 @@ class EngineEntity(
    * @param T the [Component] type to get or create.
    * @param configure inlined function with [T] as the receiver to allow additional configuration of the [Component].
    * @return the created ƒ[Component].
+   * @throws [CreateComponentException] if the engine was unable to create the component
    * @see [create]
    */
   inline fun <reified T : Component> with(configure: (@AshleyDsl T).() -> Unit = {}): T {
@@ -36,12 +38,20 @@ class EngineEntity(
 /**
  * Get or create a [Component] by calling [Engine.createComponent].
  *
+ * The [Component] must have a visible no-arg constructor.
+ *
  * @param T the type of [Component] to get or create.
  * @param configure inlined function with [T] as the receiver to allow further configuration.
  * @return an [Component] instance of the selected type.
+ * @throws [CreateComponentException] if the engine was unable to create the component
  */
-inline fun <reified T : Component> Engine.create(configure: T.() -> Unit = {}): T
-    = createComponent(T::class.java).apply(configure)
+inline fun <reified T : Component> Engine.create(configure: T.() -> Unit = {}): T {
+  return try {
+    createComponent(T::class.java)
+  } catch (e: Exception) {
+    throw CreateComponentException(T::class, e)
+  }?.apply(configure)?:throw CreateComponentException(T::class)
+}
 
 /**
  * Builder function for [Engine].
@@ -63,3 +73,5 @@ inline fun Engine.entity(configure: EngineEntity.() -> Unit = {}): Entity {
   addEntity(entity)
   return entity
 }
+
+class CreateComponentException(type: KClass<*>, cause: Throwable? = null): RuntimeException("Could not instantiate component ${type::java.name} - the component must have a visible no-arg constructor", cause)

ashley/src/test/kotlin/ktx/ashley/EnginesSpec.kt

@@ -1,7 +1,10 @@
 package ktx.ashley
 
+import com.badlogic.ashley.core.Component
+import com.badlogic.ashley.core.Engine
 import com.badlogic.ashley.core.PooledEngine
 import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.assertThatExceptionOfType
 import org.jetbrains.spek.api.Spek
 import org.jetbrains.spek.api.dsl.describe
 import org.jetbrains.spek.api.dsl.it
@@ -18,6 +21,23 @@ object EnginesSpec : Spek({
         assertThat(component.y).isEqualTo(0f)
       }
     }
+    describe("creating a component that has no no-arg constructor") {
+      @Suppress("UNUSED_PARAMETER")
+      class NoNoArgConstructorComponent(body: String): Component
+
+      it("should throw an exception if the non-pooled engine was unable to create the component") {
+        val nonPooledEngine = Engine()
+        assertThatExceptionOfType(CreateComponentException::class.java).isThrownBy {
+          nonPooledEngine.create<NoNoArgConstructorComponent>()
+        }
+      }
+
+      it("should throw an exception if the pooled engine was unable to create the component") {
+        assertThatExceptionOfType(CreateComponentException::class.java).isThrownBy {
+          engine.create<NoNoArgConstructorComponent>()
+        }
+      }
+    }
     describe("creating a component with configuration") {
       val component = engine.create<Transform> {
         x = 1f