android controller lifecycle #1065

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/ViewController.java

 import android.app.Activity;
 import android.support.annotation.Nullable;
 import android.view.View;
+import android.view.ViewTreeObserver;
 
 public abstract class ViewController {
+	public interface LifecycleListener {
+		void onCreate(ViewController viewController);
+
+		void onStart(ViewController viewController);
+
+		void onStop(ViewController viewController);
+
+		void onDestroy(ViewController viewController);
+	}
+
+	private enum LifecycleState {
+		Created, Started, Stopped, Destroyed
+	}
+
 	private final Activity activity;
 	private View view;
 	private StackController stackController;
+	private LifecycleState lifecycleState;
+	private LifecycleListener lifecycleListener;
 
 	public ViewController(Activity activity) {
 		this.activity = activity;
 
 	public View getView() {
 		if (view == null) {
-			view = onCreateView();
+			view = createView();
+		}
+		return view;
+	}
+
+	public void setLifecycleListener(LifecycleListener lifecycleListener) {
+		this.lifecycleListener = lifecycleListener;
+	}
+
+	private View createView() {
+		View view = onCreateView();
+		lifecycleState = LifecycleState.Created;
+		view.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
+			@Override
+			public boolean onPreDraw() {
+				if (lifecycleListener != null) {
+					if (lifecycleState != LifecycleState.Started) {
+						lifecycleState = LifecycleState.Started;
+						lifecycleListener.onStart(ViewController.this);
+					}
+				}
+				return true;
+			}
+		});
+		if (lifecycleListener != null) {
+			lifecycleListener.onCreate(this);
 		}
 		return view;
 	}

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/ViewControllerTest.java

 import org.junit.Test;
 
 import static org.assertj.core.api.Java6Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyZeroInteractions;
 
 public class ViewControllerTest extends BaseTest {
 
 	public void handleBackDefaultFalse() throws Exception {
 		assertThat(uut.handleBack()).isFalse();
 	}
+
+	public static class LifecycleTest extends BaseTest {
+		private ViewController controller;
+		private ViewController.LifecycleListener uut;
+
+		@Override
+		public void beforeEach() {
+			super.beforeEach();
+			Activity activity = newActivity();
+			controller = new SimpleViewController(activity, "controller");
+			uut = mock(ViewController.LifecycleListener.class);
+			controller.setLifecycleListener(uut);
+		}
+
+		@Test
+		public void onCreateView_CalledAsSoonAsPossible() throws Exception {
+			verifyZeroInteractions(uut);
+			controller.getView();
+			verify(uut, times(1)).onCreate(controller);
+		}
+
+		@Test
+		public void onStart_CalledBeforeFirstDraw() throws Exception {
+			verifyZeroInteractions(uut);
+			controller.getView().getViewTreeObserver().dispatchOnPreDraw();
+			controller.getView().getViewTreeObserver().dispatchOnPreDraw();
+			verify(uut, times(1)).onStart(controller);
+		}
+	}
+
 }