From 8953147d96087582a7fea2c5284d585e70d768df Mon Sep 17 00:00:00 2001
From: Leif Åstrand <leif@vaadin.com>
Date: Fri, 13 Nov 2015 10:58:35 +0200
Subject: Add some performance guidance to renderer javadocs.

Change-Id: I5171c6eb6360a9c85b8afbc3096d9b6c5c8f4064
---
 client/src/com/vaadin/client/renderers/Renderer.java       | 8 +++++++-
 client/src/com/vaadin/client/renderers/WidgetRenderer.java | 5 +++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/client/src/com/vaadin/client/renderers/Renderer.java b/client/src/com/vaadin/client/renderers/Renderer.java
index a3faa1e9df..b2e9acd582 100644
--- a/client/src/com/vaadin/client/renderers/Renderer.java
+++ b/client/src/com/vaadin/client/renderers/Renderer.java
@@ -35,7 +35,13 @@ import com.vaadin.client.widgets.Grid;
 public interface Renderer<T> {
 
     /**
-     * Called whenever the {@link Grid} updates a cell
+     * Called whenever the {@link Grid} updates a cell.
+     * <p>
+     * For optimal performance, work done in this method should be kept to a
+     * minimum since it will be called continuously while the user is scrolling.
+     * It is recommended to set up the cell's DOM structure in
+     * {@link ComplexRenderer#init(RendererCellReference)} and only make
+     * incremental updates based on cell data in this method.
      * 
      * @param cell
      *            The cell. Note that the cell is a flyweight and should not be
diff --git a/client/src/com/vaadin/client/renderers/WidgetRenderer.java b/client/src/com/vaadin/client/renderers/WidgetRenderer.java
index 1a33894e8e..d7219e7241 100644
--- a/client/src/com/vaadin/client/renderers/WidgetRenderer.java
+++ b/client/src/com/vaadin/client/renderers/WidgetRenderer.java
@@ -60,6 +60,11 @@ public abstract class WidgetRenderer<T, W extends Widget> extends
      * information in the widget that is cell specific. Do not detach the Widget
      * here, it will be done automatically by the Grid when the widget is no
      * longer needed.
+     * <p>
+     * For optimal performance, work done in this method should be kept to a
+     * minimum since it will be called continuously while the user is scrolling.
+     * The renderer can use {@link Widget#setLayoutData(Object)} to store cell
+     * data that might be needed in e.g. event listeners.
      * 
      * @param cell
      *            The cell to render. Note that the cell is a flyweight and
-- 
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