You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

Related Topics: ColdFusion, Adobe Flex

ColdFusion: Article

User Interface Layout in Adobe Flex 2.0

Creating a user interface is just like making a floor plan

Creating a user interface is just like making a floor plan. You have your "room," which is the screen, and you have the "furniture," which is your user interface elements. This article describes many of the ways to position those elements on the screen using XML tags (which we call MXML.)

Flex applications are written with a combination of component declarations as MXML tags and ActionScript programming code. A "component" refers to any object in Flex that has a visual aspect. Buttons, Sliders, Labels, and CheckBoxes are examples of "control" components. There are other components that are very important to the layout of a Flex application. These other components are "containers" in which you put controls to position them on the screen.

There's a Layout Manager in the Flex architecture. This is the entity that is responsible for carrying out the layout instructions. Once the components are created, the Layout Manager asks every container for its size. Each container in turn asks each child for its size. This continues until the Layout Manager has a pretty good idea of how big everything is. Then it carries out the placement instructions as best it can.

The easiest way to place components is with absolute positioning and setting the x and y coordinates. The origin, (0,0), is in the upper left-hand corner. For example, to position a button so that it's 10 pixels from the left edge and 30 pixels from the top edge, type this MXML tag:

<mx:Button label="Push Me" x="10" y="30" />

Simple enough. You can use this technique to position all of your components.

That's all well and good, but now suppose you want a layout like this:

Image A

Besides position, most components have width and height properties. To start, you could create your layout like this:

<mx:Text text="My Title Goes Here" x="35" y="10" />
<mx:DataGrid x="0" y="50" width="200" height="200" />

Now comes the question: How do I make the DataGrid take up the entire width of the application space and how do I make the DataGrid use up the rest of the height? In other words, you have no idea how big the user will make their browser. It could be 200x250. Or it could be 1024x768. It would be nice if the components could automatically expand to fill the space. Actually, that's easy. Not only can you specify the width and height of a component in pixels, you can also specify it as a percentage of the container in which they are placed. This is an important fact and we'll come back to it shortly.

<mx:DataGrid x="0" y="50" width="100%" height="100%" />

Using 100% for the width and height makes the DataGrid use up the space in those directions. When I first saw this I expected that I would have to know the height of the Text control, or the percentage of space that the Text control was using. Not necessary. The Flex Layout Manager figures it out. It knows you want the top of the DataGrid to be positioned at 50 pixels. Having a height of 100% means it takes up the rest of the vertical space. When you run this Flex application you can resize the browser and the DataGrid will adjust its size.

Image B

But what about that title Text? Suppose you'd like it to be centered above the DataGrid and move left and right as the browser window's width changes. That's easy too.

Flex has another way to position components called constraints and it's probably the method you'll use the most. Constraints let certain container components (those that allow absolute positioning) shift their content according to the parameters you specify. Using constraints is a lot better than using x, y, width, and height, because it positions the components dynamically and lets them adapt to the size of the browser window.

Let's start with the DataGrid. So far the DataGrid is at the edge of the browser space. Using constraints can give it some margins to make it look nicer:

<mx:DataGrid left="10" top="50" right="10" bottom="10" />

The constraints in this MXML tag are named left, top, right, and bottom. Each constraint gives the position, in pixels, from that edge of the container component. The tag above says DataGrid should always be 10 pixels from the left edge, 50 pixels from the top edge, 10 pixels from the right edge, and 10 pixels from the bottom edge.

Centering components uses another constraint:

<mx:Text text="My Title Goes Here" horizontalCenter="0" />

Image C

The horizontalCenter constraint is the number of pixels that the center of the component should be from the center of the container. That is, when set to 0, the center of the Text component is exactly at the center of the application. If you set horizontalCenter="-20" then the center of the Text component would be shifted left of center by 20 pixels. A positive number shifts the center of the component to the right. There's a corresponding verticalCenter constraint too.

Note: You don't have to use all the constraints with every control. Use only the ones that make sense. For example, to make a component hug the right edge, use right="0" but don't use left. If you do use both left and right the component will be stretched across the application.

Flex Builder
If you have Flex Builder 2 you can use the Design View function to easily position components.

Image D

The layout tool (lower right) allows you to give exact values for size, position, and constraint.

More Stories By Peter Ent

Peter Ent is a Web application developer specializing in Rich Internet Applications. He has more than 20 years of experience ranging from keypunches to wireless PCs.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

@ThingsExpo Stories
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Conference Guru has been named “Media Sponsor” of the 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to gre...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develop...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Large industrial manufacturing organizations are adopting the agile principles of cloud software companies. The industrial manufacturing development process has not scaled over time. Now that design CAD teams are geographically distributed, centralizing their work is key. With large multi-gigabyte projects, outdated tools have stifled industrial team agility, time-to-market milestones, and impacted P&L stakeholders.
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.