From 5487b95472e9a1c03d02d57c146895f046dc8793 Mon Sep 17 00:00:00 2001
From: Hixie <github.com@spam.hixie.ch>
Date: Mon, 28 Sep 2015 11:53:03 -0700
Subject: [PATCH] Require giving a GlobalKey to UniqueComponent

Having UniqueComponent automatically generate its own key is a trap. If
anyone ever creates a UniqueComponent in a build function (rather than
ahead of time) and forgets to pass a key, then that entire subtree is
going to be rebuilt, including layout, every time it's updated. Since
there's basically no way for us to catch this, we should at least force
the author to see the explicit "new GlobalKey()" call in their code.
---
 packages/flutter/lib/src/fn3/unique_component.dart | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/flutter/lib/src/fn3/unique_component.dart b/packages/flutter/lib/src/fn3/unique_component.dart
index c3ef366418..560d3b4477 100644
--- a/packages/flutter/lib/src/fn3/unique_component.dart
+++ b/packages/flutter/lib/src/fn3/unique_component.dart
@@ -5,7 +5,9 @@
 import 'package:sky/src/fn3.dart';
 
 abstract class UniqueComponent<T extends State> extends StatefulComponent {
-  UniqueComponent({ GlobalKey key }) : super(key: key ?? new GlobalKey());
+  UniqueComponent({ GlobalKey key }) : super(key: key) {
+    assert(key != null);
+  }
 
   T createState();