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.

 
AAPL
$102.50
Apple Inc.
+0.25
MSFT
$45.43
Microsoft Corpora
+0.55
GOOG
$571.60
Google Inc.
+2.40

MacTech Search:
Community Search:

Software Updates via MacUpdate

Skype 6.19.0.450 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
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
SlingPlayer Plugin 3.3.20.505 - Browser...
SlingPlayer is the screen interface software that works hand-in-hand with the hardware inside the Slingbox to make your TV viewing experience just like that at home. It features an array of... Read more
Get Lyrical 3.8 - Auto-magically adds ly...
Get Lyrical auto-magically add lyrics to songs in iTunes. You can choose either a selection of tracks, or the current track. Or turn on "Active Tagging" to get lyrics for songs as you play them.... Read more
Viber 4.2.2 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device,... Read more
Cocktail 7.6 - General maintenance and o...
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
LaunchBar 6.1 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more

Latest Forum Discussions

See All

Rhonna Designs Magic (Photography)
Rhonna Designs Magic 1.0 Device: iOS Universal Category: Photography Price: $1.99, Version: 1.0 (iTunes) Description: Want to sprinkle *magic* on your photos? With RD Magic, you can add colors, filters, light leaks, bokeh, edges,... | Read more »
This Week at 148Apps: August 25-29, 2014
Shiny Happy App Reviews   | Read more »
Qube Kingdom – Tips, Tricks, Strategies,...
Qube Kingdom is a tower defense game from DeNA. You rally your troops – magicians, archers, knights, barbarians, and others – and fight against an evil menace looking to dominate your kingdom of tiny squares. Planning a war isn’t easy, so here are a... | Read more »
Qube Kingdom Review
Qube Kingdom Review By Nadia Oxford on August 29th, 2014 Our Rating: :: KIND OF A SQUARE KINGDOMUniversal App - Designed for iPhone and iPad Qube Kingdom has cute visuals, but it’s a pretty basic tower defense game at heart.   | Read more »
Fire in the Hole Review
Fire in the Hole Review By Rob Thomas on August 29th, 2014 Our Rating: :: WALK THE PLANKUniversal App - Designed for iPhone and iPad Seafoam’s Fire in the Hole looks like a bright, 8-bit throwback, but there’s not enough booty to... | Read more »
Alien Creeps TD is Now Available Worldwi...
Alien Creeps TD is Now Available Worldwide Posted by Ellis Spice on August 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Dodo Master Review
Dodo Master Review By Jordan Minor on August 29th, 2014 Our Rating: :: NEST EGGiPad Only App - Designed for the iPad Dodo Master is tough but fair, and that’s what makes it a joy to play.   | Read more »
Motorsport Manager Review
Motorsport Manager Review By Lee Hamlet on August 29th, 2014 Our Rating: :: MARVELOUS MANAGEMENTUniversal App - Designed for iPhone and iPad Despite its depth and sense of tactical freedom, Motorsport Manager is one of the most... | Read more »
Motorsport Manager – Beginner Tips, Tric...
The world of Motorsport management can be an unforgiving and merciless one, so to help with some of the stress that comes with running a successful race team, here are a few hints and tips to leave your opponents in the dust. | Read more »
CalPal Update Brings the App to 2.0, Add...
CalPal Update Brings the App to 2.0, Adds Lots of New Stuff Posted by Ellis Spice on August 29th, 2014 [ permalink ] | Read more »

Price Scanner via MacPrices.net

Apple now offering refurbished 21-inch 1.4GHz...
The Apple Store is now offering Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
Save $50 on the 2.5GHz Mac mini, on sale for...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
The Rise of Phablets
Carlisle & Gallagher Consulting Group, a businesses and technology consulting firm focused solely on the financial services industry, has released an infographic depicting the convergence of... Read more
Bad Driver Database App Allows Good Drivers t...
Bad Driver Database 1.4 by Facile Group is a new iOS and Android app that lets users instantly input and see how many times a careless, reckless or just plain stupid driver has been added to the... Read more
Eddy – Cloud Music Player for iPhone/iPad Fre...
Ukraine based CapableBits announces the release of Eddy, its tiny, but smart and powerful cloud music player for iPhone and iPad that allows users to stream or download music directly from cloud... Read more
A&D Medical Launches Its WellnessConnecte...
For consumers and the healthcare providers and loved ones who care for them, A&D Medical, a leader in connected health and biometric measurement devices and services, has launched its... Read more
Anand Lal Shimpi Retires From AnandTech
Anand Lal Shimpi, whose AnandTech Website is famous for its meticulously detailed and thoroughgoing reviews and analysis, is packing it in. Lal Shimpi, who founded the tech site at age 14 in 1997,... Read more
2.5GHz Mac mini, Apple refurbished, in stock...
The Apple Store has Apple Certified Refurbished 2.5GHz Mac minis available for $509, $90 off MSRP. Apple’s one-year warranty is included, and shipping is free. Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. 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
*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
*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
*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
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.