Layout Best Practices

An Oracle JDeveloper Best Practices Document
August, 2008

Best Practices	Layout Best Practices
Best Practices Revision	1.0
Technologies	JDeveloper, ADF, ADF Faces
Keywords	Layout
Forum	Pattern Team
Publish date	August 2008

Problem Description

A developer needs to be able to develop a Rich Client Interface and avoid basic layout issues that tend to be pervasive across screens and applications. There are a number of low-level layout issues within ADFv that:

Tend to repeat themselves across screens and across applications.
Impact perception of usability, quality, and fit ‘n’ finish.
Are annnoying to users in the aggregate – no single item is terrible, but a collection of 6 items, repeating themselves on multiple screens gets frustrating and detracts from the message.

In most cases, there’s a simple approach and best practice that will assist developers in avoiding these pitfalls.

This document discusses basics of page layout and provides guidance to avoid common browser pitfalls, a recommended process for creating layouts, and illustrates layout examples.

Technical Best Practice Description

This Layout Best Practices document is not necessarily a pattern but instead, a laundry list of known layout issues that are encountered when developing a Rich Client Interface and, how to avoid these pitfalls in your application development.

Various ADF Components are described and demonstrated throughout this document including document, showDetailItem, decorativeBox, panelSplitter, panelStretchLayout, panelBorderLayout and so on. Not one component by itself but many are combined to achieve the desired layout for a screen and / or an application.

Best Practices: The User Experience

To save a great deal of development grief and enjoy reduced maintenance costs:

Never try to stretch something vertically when inside of a flowing (non-stretched) container. Attempting to do this will result in inconsistent behavior across web browsers.
Never specify a height value with percent units. Instead, define such stretching declaratively as by following the process outlined below.
Never use the "position" style.
Take advantage of the layout pattern examples for guidance on how best to create a desired layout. Be sure to click on the "View Page Source" and the "View Template Source" links in the top right corner of the demo to see what tags and attributes are used as well as what the component structure looks like for each specific pages.

Process for Creating Layouts: The Artifacts

Create a stretchable outer frame

Build up the outer structure of your page using a structure of components that support being stretched and also stretch their children.

Each layout or panel component's tag documentation will identify whether this is supported and how to achieve it in its "Geometry Management" documentation. Some components have attributes to determine whether children will be stretched or not. For example:

document has its maximized attribute. Try the maximized attribute NOT SET on the document component.

showDetailItem has its stretchChildren attribute.

Typically you would use various combinations of the decorativeBox, panelSplitter, and panelStretchLayout components inside of your document component to create the stretchable outer frame.

Also, consider using pageTemplates, declarative components, and regions for reuse and centralized maintenance.

Create flowing islands

Inside of the stretchable structure created in step 1, you can create islands of flowing (non-stretched) components. To make this transition from stretching to flowing, use panelGroupLayout with layout="scroll" since it supports being stretched but will not stretch its children.

For a reliable page layout:

Do not specify heights using percent units. Instead, use components that stretch their children.

Do not use the position style.

Do not attempt to stretch anything vertically inside of these flowing islands.

Many leaf components do not make sense by themselves. For example, if you have a series of input components, you would never want to just place these in a panelGroupLayout because it would be much better for usability if you placed them in a panelFormLayout so the labels and fields will line up.

A sample list of components that cannot be reliably stretched includes:

Most input components

panelBorderLayout

panelBox

panelFormLayout

panelGroupLayout with layout="default" or layout = "horizontal"

panelHeader - see the Stretched Header example for a situation where content below a header is stretched

panelLabelAndMessage

panelList

Apache MyFaces Trinidad HTML Component - tableLayout

JSF HTML Component - panelGrid

Customize the appearance of components

Appearance may be customized using the following mechanisms:

Use themed decorativeBox components to organize your page layers with visual distinction and decorative borders as seen in some of the sample skins. Note that not all skins have alternative themes so you may not see any distinction. If your decorativeBox components are not showing up with different colored backgrounds and you know that you are using a skin that has definitions for alternate themes, you might be missing a web.xml context-param setting for "oracle.adf.view.rich.tonalstyles.ENABLED" being set to false. Your document component also has a theme attribute so you can use it to change the main background styling of your page.

Use a custom skin for consistently modified appearances if the existing skin doesn't provide all that you need.

For instance-specific alternative styling, use the styleClass attribute. Keep the corresponding style definitions in an easy-to-maintain location such as in a custom skin, in the metaContainer facet of the document component, or as close to the top of the page as possible for optimal performance.

As a last resort, use component attributes such as inlineStyle, contentStyle, and labelStyle. These are less declarative, harder to maintain, contribute more to the page's raw HTML size, and may not even be needed if one or more of the above mechanisms are used.

Styles are directly processed by the web browser, which gives you a great deal of power but at the cost of being less declarative and error-prone. The browsers do not support all styles on all elements and certain combinations of styles produce non-obvious results. Here is some guidance on style configurations to avoid:

Component	Situation to Avoid
*	An inlineStyle with a "height" value with "%" units
*	An inlineStyle with "height", "top", and "bottom" values
*	An inlineStyle with "width", "left", and "right" values
*	An inlineStyle with a "position" value
Child being stretched by a parent component	An inlineStyle with "width" or "height" values

* Note: Avoid when possible throughout.

Scrolling:

You should only have scrollbars around flowing island content. The recommended transition component for switching from a stretching outer frame into a flowing island is the panelGroupLayout with layout="scroll". If the contents of this panelGroupLayout cannot fit in the space allocated, the browser will determine whether scrollbars are needed and will add them automatically.

It is not recommended that you nest scrolling panelGroupLayout components because this will make the user see multiple scrollbars. Also, this should only be used at transitions from stretching to flowing areas and since you should not have stretching areas inside of flowing areas, you would generally never end up with nested scrollbars. It is best to minimize the number of areas that a user must scroll in order to see what he or she is looking for. Take time to consider what scrolling the user will need. In cases where undesired scrollbars exist, you may want to simply change the layout attribute of that panelGroupLayout to "vertical".

There is a known, unresolved scrolling issue that has been logged against Internet Explorer 7.0.5730.11. If a scrolling box has contents that are set to be as wide as the containing box and if the contents are large enough to warrant the need for a vertical scrollbar, an unnecessarily needed horizontal scrollbar will be added. The browser is failing to adjust the width of the contents for the presence of the vertical scrollbar and thus a horizontal scrollbar appears. This horizontal scrollbar lets you scroll the small amount of space equal to the width of the vertical scrollbar. Workarounds involve setting the widths of the contents to be smaller than full width so that the browser has enough space for a vertical scrollbar to fit. For example, you may want to add a styleClass that only shows up in Internet Explorer that assigns "width: 90%" on an af:panelHeader tag. You can achieve this with code like this:

<af:group rendered="#{adfFacesContext.agent.agentName=='ie'}"><![CDATA[ <style type="text/css"> .MyInternetExplorerWorkaround { /* Workaround for bug in IE 7.0.5730.11 which incorrectly calculates the need for horizontal scrolling. */ width: 90%; } </style> ]]></af:group>
... <af:panelHeader text="Introduction" styleClass="MyInternetExplorerWorkaround"> ... </af:panelHeader>

Margins, borders, padding:

Thanks to the browser's "CSS Box Model rules", it is much harder to define margins, borders, and padding on your components than what you might expect. Refer to the Navigation-Master-Detail, Tiled Flowing, and Tiled Stretching layout pattern examples for various mechanisms to apply padding.

In many cases, to apply these kinds of styles, you need to use multiple components together. In a scrolling area, adding an extra panelGroupLayout with layout="vertical" with the padding defined on it, inside of the outer layout="scroll" panelGroupLayout, will be required. In a stretching area, you may need to wrap a component inside of a panelStretchLayout with spacers in its top, start, end, and bottom facets for the padding.

Related Demos & Documentation

Demonstrations Based on JDeveloper 11 Release 1 are available and illustrate much of the discussion above.

Web UI Developer's Guide for Oracle ADF

Tag Documentation Related to the Artifacts

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