TweetFollow Us on Twitter

The LayerGroup

Volume Number: 15 (1999)
Issue Number: 4
Column Tag: Programming Techniques

The LayerGroup

by Spec Bowers

A very simple, flexible and useful widget

Introduction

This article describes a very useful widget which I call a "LayerGroup." The name is derived from the Layers that many drawing programs provide, and from a RadioGroup. A LayerGroup contains and controls multiple Layers, only one of which is visible at a time. Each layer in turn can contain other controls. When a layer is made visible all of its embedded controls become visible, When a layer is hidden all of its embedded controls are hidden. The effect of hiding one layer and showing another layer is to swap in and out a set of controls.

What makes a LayerGroup so useful is that it encapsulates behavior that appears in a great many applications. The appearance varies from one application to another but the behavior is the same: the set of available controls is swapped in and out. Using a LayerGroup makes it very easy to implement this kind of behavior without reinventing the wheel.

What makes a LayerGroup so flexible is that it implements only the behavior, not the visible appearance. The appearance is determined by a control external to the LayerGroup. That control can be anything that produces an integer, such as a TabControl, a Popup, or a Listbox. Figure 1 and the example application show several kinds of LayerGroup.


Figure 1. Three kinds of LayerGroups.

These LayerGroups all look different but the implementations are essentially the same. The Tab Panel is a TabControl with a nested LayerGroup. The group in turn contains three layers, each with its own set of controls. The Tab Control produces a 1, 2, or 3. That integer is passed to the LayerGroup which shows that one layer. Similarly, the Popup Group Box has a nested LayerGroup. The value of the Popup is passed to the LayerGroup. For the Listbox example, the LayerGroup is not nested but the implementation is otherwise the same: selecting a row causes the row number to be passed to the LayerGroup.

The example application has a fourth LayerGroup which is controlled by a set of edit fields. The item number of whichever edit field is active is used to control the LayerGroup. The effect is that tabbing to or clicking an edit field causes the LayerGroup to display picture and text describing what to enter into that edit field.

In these examples the content of each layer is just one or two items but there could be any number of items. Real applications might have a dozen or more items in each layer. The LayerGroup controls the layers; each layer controls the items in that layer.

The LayerGroup behavior can be seen in many real-life applications. Most likely, the various programmers had to write special-purpose code for each application. The only reusable code I have seen along these lines is in Apple's sample code for the AppsToGo framework, <http://developer.apple.com/dev/techsupport/source/AppsToGo.html>. That code, written prior to the Appearance Manager, is quite complex. With Appearance, the code is simple.

The Code

We implemented LayerGroups going straight to Apple's Appearance toolbox and separately for PowerPlant. It would be very easy to implement it for any other class library that supports nested views and hiding and showing. (I am told that the Windows MFC library has such primitive support for nesting that implementing this LayerGroup is complicated.)

//-----
void   SetLayerGroupValue (
   ControlHandle   inControl,
   SInt16      inValue)   // 1-based
{
   SInt16      numLayers = 0;
   SInt16      i;
   ControlHandle   layer;

   CountSubControls (inControl, &numLayers);
   for (i = 1; i <= numLayers; i++) {
      GetIndexedSubControl (inControl, i, &layer);
      if (i == inValue) {
         ActivateControl (layer);
         ShowControl (layer);
      } else {
         HideControl (layer);
         DeactivateControl (layer);
      }
   } // for
   Draw1Control (inControl);
}

That's all it takes to implement a LayerGroup. The code is this simple because the Appearance Manager supports embedded controls. Layers are embedded within the LayerGroup; items are embedded within layers.

The LayerGroup and the layers are vanilla User Pane controls with no visible appearance of their own. We did not write any code for a layer. The Appearance Manager does all the work. When a layer is hidden or shown the Appearance Manager hides or shows whatever controls are embedded in that layer.

The ActivateControl and DeactivateControl calls we added to work around what is probably a minor bug in the Appearance Manager. When an active edit text control was in a hidden layer we saw a blinking insertion point even though the edit text was hidden. The cure is to deactivate a layer. That deactivates the embedded controls.

For PowerPlant, the code is very similar. The layer group is a very simple subclass of LView. The layers are ordinary LViews. Like Appearance (for quite some time prior to Appearance) PowerPlant supports nested items. Hiding (or showing) an LView hides (or shows) all the items nested within the LView. All that CLayerGroup needs is a SetValue member function that is much like the SetLayerGroupValue when using Appearance.

Making a LayerGroup

It is very easy to create a LayerGroup:

  • Make a LayerGroup control.
  • Make Layers nested within the LayerGroup.
  • For each Layer, make whatever nested items you want.

You could create these controls programatically but obviously the preferred way is to create the controls from resources. For Appearance, dialogs use DITL and CNTL resources. The location and size of controls implies the nesting order. (To nest a control, specify coordinates that are completely within a preceding item.) CNTL resources are also used for windows but you have to write code to create each control and to specify how the controls are embedded. For PowerPlant, both windows and dialogs are created from PPob resources.

For a Dialog Using Appearance

Create DITL and CNTL resources. The LayerGroup and Layers are User Pane controls (procID 256) with Initial Value 2 to specify that the control supports embedding.

In your code, create the dialog via GetNewDialog:

      mDialog = GetNewDialog (inResID, nil, (WindowPtr) -1L);

For convenience later, get a ControlHandle for the LayerGroup:

      GetDialogItemAsControl (mDialog, kLayerGroup,
                                          &mLayerGroupHandle);

Respond to a hit in the controlling item (e.g. the TabControl, Popup, or Listbox) by changing the LayerGroup's value:

      choice = GetControlValue (mControllerHandle);
      SetLayerGroupValue (mLayerGroupHandle, choice);

For a Window Using Appearance

Create CNTL resources. The LayerGroup and Layers are User Pane controls (procID 256) with Initial Value 2 to specify that the control supports embedding. In your code, create each control by GetNewControl, then EmbedControl:

      mLayer1Handle = GetNewControl (CNTL_Layer1, window);
      EmbedControl (mLayer1Handle, mLayerGroupHandle);

Respond to a click in the controlling item (e.g. the TabControl, Popup, or Listbox) by changing the LayerGroup's value:

      LGetSelect (true, &selectedCell, list);
      layer = selectedCell.v + 1;      // layers are 1-based
      SetLayerGroupValue (mLayerGroupHandle, layer);

The Appearance SDK provides an FKEY for creating a dump of the control hierarchy. This is what the Listbox example looks like:

Root pane
   Control pane (Scroll Bars)
   Control pane (List Box)
   Control pane (User Pane) - LayerGroup
      Control pane (User Pane) - Layer one
         Control pane (Push Buttons)
         Control pane (Static Text)
      Control pane (User Pane) - Layer two
         Control pane (Group Box)
            Control pane (Radio Group)
               Control pane (Push Buttons)
               Control pane (Push Buttons)
      Control pane (User Pane) - Layer three
         Control pane (Static Text)
         Control pane (Edit Text)
      Control pane (User Pane) - Layer four
         Control pane (Popup Button)

For PowerPlant

Create PPob resources. The LayerGroup's classID is 'LGrp'. (A custom CTYP resource for Constructor is with the source code.) Each layer is an LView (classID 'view').

In your code, register the LayerGroup and LView classes:

      RegisterClass_(CLayerGroup);
      RegisterClass_(LView);

For convenience later, get a pointer to the LayerGroup:

      mLayerGroup = (CLayerGroup*) FindPaneByID ('XXXX');

In the ListenToMessage method respond to a hit in the controlling item (e.g. the TabControl, Popup, or Listbox) by changing the LayerGroup's value:

      case msgTabs:
         mLayerGroup->SetValue (mTabControl->GetValue ());

Variations

A simple variation is to create only two layers with the first one empty. When controlled by a checkbox the effect would be to hide or show a set of controls.

For PowerPlant, we implemented a variation which uses a pane ID instead of an ordinal number. It finds and shows the layer with the matching pane ID. We also specified a particular pane ID as a default, a layer to be shown if no other layers match the requested pane ID.

If there are many layers and/or many items within layers and if running on a slowish machine, the cost to create all of the layers with all of their items might be noticeable. A performance enhancement would be to defer creating the items within a layer until that layer is first made visible. If the user happens not to show some layers then there would be no time spent making the items within those layers.

A Plug

These examples were created using AppMaker, which generated both the resources and the source code. Whether you use AppMaker or you do it by hand, I think you will find that the LayerGroup is a useful widget to have in your toolbox.


Spec Bowers is the founder, cook, and chief bottle washer at Bowers Development. He has been developing programming tools for most of his career. You can contact him at bowersdev@aol.com or see the web page at http://members.aol.com/bowersdev.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Ember 1.8.3 - Versatile digital scrapboo...
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
Apple iTunes 12.1 - Manage your music, m...
Apple iTunes lets you organize and play digital music and video on your computer. It can automatically download new music, app, and book purchases across all your devices and computers. And it's a... Read more
LibreOffice 4.4.3 - Free, open-source of...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
FoldersSynchronizer 4.2.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Simon 4.0.2 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
Cocktail 8.1.2 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cyberduck 4.6.4 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more
Herald 5.0.2 - Notification plugin for M...
Note: Versions 2.1.3 (for OS X 10.7), 3.0.6 (for OS X 10.8), and 4.0.8 (for OS X 10.9) are no longer supported by the developer. Herald is a notification plugin for Mail.app, Apple's Mac OS X email... Read more
DEVONthink Pro 2.8.3 - Knowledge base, i...
Save 10% with our exclusive coupon code: MACUPDATE10 DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research... Read more
Boom 2 1.0.1 - System-wide pro audio app...
Boom 2 is a system-wide volume booster and equalizer app that is designed especially for OS X 10.10 Yosemite. It comes with a smart interface, self-calibrates itself according to your Mac, offers... Read more

Playworld Superheroes Review
Playworld Superheroes Review By Tre Lawrence on January 30th, 2015 Our Rating: :: HERO CRAFTINGUniversal App - Designed for iPhone and iPad It’s all about the imagination, fighting bad creatures — and looking good while doing so.   | Read more »
Join the SpongeBob Bubble Party in this...
Join the SpongeBob Bubble Party in this New Match 3 Bubble Poppin’ Frenzy Posted by Jessica Fisher on January 30th, 2015 [ permalink ] | Read more »
Handpick Review
Handpick Review By Jennifer Allen on January 30th, 2015 Our Rating: :: TANTALIZING SUGGESTIONSiPhone App - Designed for the iPhone, compatible with the iPad Handpick will make you hungry, as well as inspire you to cook something... | Read more »
Storm the Halls of Echo Base in First St...
Storm the Halls of Echo Base in First Star Wars: Galactic Defense Event Posted by Jessica Fisher on January 30th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Contradiction Review
Contradiction Review By Tre Lawrence on January 30th, 2015 Our Rating: :: SPOT THE LIEiPad Only App - Designed for the iPad Contradiction is a live action point and click adventure that’s pretty engaging.   Developer: Tim Follin... | Read more »
Unlock Sunshine Girl in Ironkill with th...
Unlock Sunshine Girl in Ironkill with this special 148Apps code Posted by Rob Rich on January 29th, 2015 [ permalink ] Robo-fighter Ironkill has been out on iOS a | Read more »
Crossroad Zombies Review
Crossroad Zombies Review By Jordan Minor on January 29th, 2015 Our Rating: :: CROSSWALKING DEADiPad Only App - Designed for the iPad Crossroad Zombies is a rough draft of a cool genre mash-up.   | Read more »
Blood Brothers 2 – Tips, Cheats, and Str...
War is hell: Is it the kind of hell you want to check out? Read our Blood Brothers 2 review to find out! Blood Brothers 2, DeNA’s follow-up to the original Blood Brothers, is an intriguing card collecting / role-playing / strategy hybrid. There’s... | Read more »
Blood Brothers 2 Review
Blood Brothers 2 Review By Nadia Oxford on January 29th, 2015 Our Rating: :: AN AGGRAVATING RELATIVEUniversal App - Designed for iPhone and iPad Blood Brothers 2 is built on a simple, solid foundation, but its free-to-play system... | Read more »
I AM BREAD, the Toast of the Town, is Ro...
Have you ever dreamt of being deliciously gluten-y? Do you feel passionate about Rye and Wheat? The guys at Bossa Studios do and that is why they are bringing I AM BREAD to iOS soon. The loafy app will feature all the new content that is being... | Read more »

Price Scanner via MacPrices.net

Intel Aims to Transform Workplace With 5th-Ge...
Intel Corporation today announced the availability of its 5th generation Intel Core vPro processor family that provides cutting-edge features to enable a new and rapidly shifting workplace. To meet... Read more
iOS App Sharalike Introduces New Instant Smar...
Sharalike slideshow and photo management software for iOS, is making it easier than ever to create shareable meaningful moments with its new instant SmartShow technology. Staying organized is a goal... Read more
Apple Becomes World’s Largest Smartphone Vend...
According to the latest research data from Strategy Analytics, as global smartphone shipments grew 31 percent annually to reach a record 380 million units in the fourth quarter of 2014. Apple became... Read more
Cut the Cord: OtterBox Resurgence Power Case...
Dead batteries and broken phones are two of the biggest issues for smartphone users today. Otterbox addresses both with the new Resurgence Power Case for Apple iPhone 6, promising to make those panic... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1199.99 save $100 - 13″ 2.6GHz/... Read more
15-inch 2.5GHz Retina MacBook Pro on sale for...
 B&H Photo has the 15″ 2.5GHz Retina MacBook Pro on sale for $2319.99 including free shipping plus NY sales tax only. Their price is $180 off MSRP, and it’s the lowest price available for this... Read more
Back in stock: Refurbished iPod nanos for $99...
The Apple Store has Apple Certified Refurbished 16GB iPod nanos available for $99 including free shipping and Apple’s standard one-year warranty. That’s $50 off the cost of new nanos. Most colors are... Read more
Apple lowers price on refurbished 256GB MacBo...
The Apple Store has lowered prices on Apple Certified Refurbished 2014 MacBook Airs with 256GB SSDs, now available for up to $200 off the cost of new models. An Apple one-year warranty is included... Read more
New Good Management Suite Simplifies Enterpri...
Good Technology has announced the availability of the Good Management Suite, a comprehensive cross-platform solution for organizations getting started with mobile business initiatives. Built on the... Read more
15-inch 2.0GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished previous-generation 15″ 2.0GHz Retina MacBook Pros available for $1489 including free shipping plus Apple’s standard one-year warranty. Their price is... Read more

Jobs Board

*Apple* Solutions Consultant- Retail Sales (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
SW QA Engineer - *Apple* TV - Apple (United...
**Job Summary** The Apple TV team is looking for experienced Quality Assurance Engineers with a passion for delivering first in class home entertainment solutions. **Key Read more
*Apple* Retail - Multiple Positions(US) - Ap...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you re also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.