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

MacUpdate Desktop 6.0.8 - Search and ins...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
BitTorrent Sync 2.1.1 - Sync files secur...
BitTorrent Sync allows you to sync unlimited files between your own devices, or share a folder with friends and family to automatically sync anything. File transfers are encrypted. Your information... Read more
Quicksilver 1.3.0 - Application launcher...
Quicksilver is a light, fast and free Mac application that gives you the power to control your Mac with keystrokes alone. Quicksilver allows you to find what you need quickly and easily, then act... Read more
iWatermark Pro 1.72 - Easily add waterma...
iWatermark Pro is the essential watermarking app for professional, business, and personal use. iWatermark, is the number 1 and only watermarking tool available for all 4 platforms iPhone/iPad, Mac,... Read more
RapidWeaver 6.3 - Create template-based...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Adobe Photoshop CC 2015 16.0.1 - Profess...
Photoshop CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Photoshop customer). Photoshop CS6 is still available for purchase (... Read more
Together 3.4.6 - Store and organize all...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Smart storage. With simple drag-and-drop functionality,... Read more
Monosnap 3.1.0 - Versatile screenshot ut...
Monosnap lets you capture screenshots, share files, and record video and .gifs! Capture: Capture full screen, just part of the screen, or a selected window Make your crop area pixel perfect with... Read more
Cocktail 8.5.1 - 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
Vienna 3.0.6 :5eaf312: - RSS and Atom ne...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more

Five Nights at Freddy's 4 has Been...
In keeping with tradition, Five Nights at Freddy's 4 has made its way to the App Store with zero warning fanfare. Honestly I'd be disappointed it if happened any other way at this point. [Read more] | Read more »
Doom & Destiny Advanced (Games)
Doom & Destiny Advanced 2.3.4.0 Device: iOS Universal Category: Games Price: $.99, Version: 2.3.4.0 (iTunes) Description: ---SUPER GIGA LAUNCH DISCOUNT! Get it now for cheap or pay more later!---An additional 143 MB download is... | Read more »
Five Nights at Freddys 4 (Games)
Five Nights at Freddys 4 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: This time, the terror has followed you home. | Read more »
This Week at 148Apps: July 27-31, 2015
Winding Down July With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
You'll Want to Keep an Eye Out for...
If you're the kind of person who had fun hunting down and completing all the codex puzzles in Assassin's Creed 2, then are you ever in for a treat. The Guides looks like it's going to be a very robust collection of similarily odd, seemingly... | Read more »
Vivid Games has Announced Real Boxing 2...
The original Real Boxing was a pretty impressive bit of fisticuffs, but if the trailer Vivid Games is showing off for GamesCom is any indication Real Boxing 2 is going to be even better. [Read more] | Read more »
PAC-MAN Championship Edition DX - Tips,...
[Read more] | Read more »
Card King: Dragon Wars - Tips, Tricks an...
[Read more] | Read more »
Pac-Man Championship Edition DX has brou...
Bandai Namco has released Pac-Man Championship Edition DX on iOS and Android, which features the classic arcade gameplay that we've all grown to love. Pac-Man Championship Edition DX can be enjoyed in much shorter bursts than the arcade versions... | Read more »
Cosmonautica (Games)
Cosmonautica 1.1 Device: iOS Universal Category: Games Price: $6.99, Version: 1.1 (iTunes) Description: Cast off! Are you ready for some hilarious adventures in outer space? | Read more »

Price Scanner via MacPrices.net

MacBook 12 Retina Pundit’s New Favorite Mac
If you’re eyeing the purchase of a new 12-inch Retina MacBook, but wondering if you can live with a single USB-C port, 2011-level CPU performance, and the unorthodox keyboard, you should find... Read more
PDF Element Tool Kit For PDF For Windows 10,...
South Surrey, British Columbia based software developer Wondershare has posted an interesting infographic tracking the development of Microsoft’s flagship Windows operating system over the years,... Read more
27-inch 3.5GHz 5K iMac on sale for $81 off MS...
Adorama has the 27″ 3.5GHz 5K iMac on sale for $2218, $81 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more
Back-to-School with Tablet and Smartphone Acc...
Belkin helps you prepare for the coming school year with a wide variety of the latest mobile and tablet accessories to outfit both grade school and college students. The line-up includes charging... Read more
11-inch MacBook Airs on sale for $100 off MSR...
Best Buy has 11-inch MacBook Airs on sale for $100 off MSRP. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - 11″ 1.6GHz... Read more
iPad Air 2 on sale for up to $100 off MSRP
Best Buy has iPad Air 2s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices available for online... Read more
Sale! 13-inch MacBook Pros on sale for $100 o...
B&H Photo has 13″ MacBook Pros on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz/500GB MacBook Pro: $999.99 save $100 - 13″ 2.7GHz/128GB Retina... Read more
Sale! Save $100 on 13-inch MacBook Airs this...
B&H Photo has the 13″ 1.6GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model.... Read more
Worldwide Tablet Market Decline Continues, Ap...
The worldwide tablet market declined -7.0% year-over-year in the second quarter of 2015 (2Q15) with shipments totaling 44.7 million units according to preliminary data from the International Data... Read more
TP-LINK TL-PA8030P KIT Powerline Featuring Ho...
Consumer and business networking products provider TP-LINK is now shipping its TL-PA8030P KIT AV1200 3-Port Gigabit Passthrough Powerline Starter Kit that expands your home’s network over its... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
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
Infrastructure Engineer - *Apple* /Mac - Hil...
Infrastructure Engineer - Apple /Mac Job Code: 1608 # of openings: 1 Description Our fortune 500 client is looking to hire an experienced Infrastructure Engineer to join Read more
Executive Administrative Assistant, *Apple*...
…supporting presentation development for senior leadership. * User experience with Apple hardware and software is preferred. Additional Requirements The following list Read more
*Apple* Bus Company is now hirin - Apple Bus...
Apple Bus Company is now hiring school bus drivers in the Pettis County area. Class B CDL preferred. Free training provided. No nights or weekends required. Flexible Read more
*Apple* Certified Mac Technician - Updated 6...
…and friendly, hands-on technical support to customers troubleshooting and repairing Apple /Mac products with courtesy, speed and skill. Use your problem-solving skills Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.