TweetFollow Us on Twitter

November 93 - TDialogBehaviors

TDialogBehaviors

Bob Hablutzel

This article is the first article in what I hope will be a regular series of technical questions and answers on object oriented programming. The intent of this column is to go beyond simple answers. I intend to take a question, answer it, and then use that question as a springboard to a more general discussion on programming. I hope you find the results interesting.

The first articles will be culled from frequently asked questions on MacApp3Tech$, but I need your questions! I can be reached electronically at AppleLink: B.HABLUTZEL; by telephone at 708.328.0130; or by post at Bob Hablutzel, Hablutzel Consulting, 606 Asbury, Evanston, IL, USA 60202.

Q: I need to create a modal dialog using MacApp 3.0. I create the dialog using ViewEdit, but when I attempt to pose the dialog it opens briefly and immediately closes. How can I create a modal dialog?

A: Modal dialogs in MacApp 3.0 are handled with a TDialogBehavior, which is attached to the dialog window. This behavior is responsible for receiving and handling keystrokes, looking for keystrokes that dismiss the dialog, and sending events off to the appropriate control.

The problem with ViewEdit (in this case) is that it does not attach a TDialogBehavior to the dialog when it is created. When TWindow::PoseModally() is called, the first thing it does is attempt to locate the dialog behavior; if this lookup fails it closes the window and returns immediately (returning kNoIdentifier as the dismisser).

There are a few work-arounds for this. In ViewEdit, you can add a TDialogView to the window. TDialogView is really not required in MacApp 3.0; it is a holdover from the old mechanisms in MacApp 2.0. However, if there is one in the window, it will cause the TDialogBehavior to be added when the window is opened.

Alternatively, you can create the TDialogBehavior yourself, and attach it to the window before the TWindow::PoseModally() method is called. When you create the dialog behavior, you have to supply the identifiers for the default and cancel items (in the call to IDialogBehavior()). Once this behavior is added to the window, TWindow::PoseModally() can be called.

You can also call TWindow::SetModality() before calling TWindow::PoseModally(). This method will create the dialog behavior if none exists. However, this routine may not properly set up the default and cancel identifiers; you would then have to call TWindow::GetDialogBehavior() to retrieve the dialog, and stuff the identifiers into its fCancelItem and fDefaultItem fields.

Even if you do all of this, the dialog will still not dismiss properly unless you change the default event for the dismissing control to mDismiss (==34). So if you use ViewEdit to create the dialog, you need to change the event number for the control by hand. If you leave the control at its default event number (mButton for TButtons), the control will activate, but the dialog will not dismiss.

Finally, the best solution is to avoid using ViewEdit. Either AdLib or IcePick (3.0) will add the dialog behavior to the window when you use them to create the dialog. Using either of these products will ensure that the dialog has the appropriate behavior. These programs will also take care of changing the event number for the dismissing controls to mDismiss for you. (Both these applications are available from MADA).

More About TDialogBehavior

It is somewhat interesting to notice the actual mechanism used to handle the dismissing of the modal dialogs. The TDialogBehavior does not in itself dismiss the dialog, which as we will see in a second has some interesting implications. The TDialogBehavior simply activates the control that is designated as the default (or cancel) item. It does this by sending the control its default event number. The control then accepts the event, reacts appropriately (in the case of a TButton, it flashes), and sends the event up the event chain.

The event eventually reaches the TDialogBehavior attached to the window, which checks the see if the event is mDismiss. Notice that this is the first time that the behavior checks the event type. If the event is mDismiss, the behavior records the identifier of the source of the event in the fDismisser field, and ends the modal posing. TWindow::PoseModally(), which started the modal posing in the first place, retrieves the value of the TDialogBehavior::fDismisser field, and returns that as the result of the modal posing.

What is interesting about all this is that TDialogBehavior does not necessarily have to be used with modal dialogs; it can be used with modeless dialogs just as easily. When the return key is struck, for example, the default item will be invoked. If you attach a behavior to the default control that intercepts that control's default event number, you can quickly and easily create modeless dialogs that contain default (and closing) items.

Take, for example, a drawing application that supports 1° rotations. A modeless dialog could be created that presents the user with the number of degrees of rotation, and a default Rotate button. Every time the user strikes the return key, the Rotate button would be activated. You could attach a behavior to the Rotate button that checks for events where (a) the source of the event is the owner of the behavior, and (b) the event number matches the default event number (fEventNumber) of the owner. When it receives an event that matches this criteria, it would create whatever command was responsible for the rotation of the object, and post it to the application.

The question of where to attach the behavior is an interesting one. The behavior can be attached anywhere in the event chain and still function properly. It is mostly a question of style to decide where the behavior best fits.

For example, if the behavior is attached to the button itself, it will clearly get the event that the button generates. However, if the button does not handle the event, it will pass the event up the event chain; for views this means that the superview will receive the event. This passing along continues through each respective superview until someone handles the event, the TWindow used to draw the dialog will get the event eventually, provided no-one else has handled it.

In the example above, there are two ways of designing the interface. If the TNumberText used to hold the rotation amount is just a generic TNumberText, then it would make sense to have the behavior attached to the dialog. This would allow the dialog access to a child view to retrieve the rotation amount. (If the behavior were attached to the button, it would have to access a sibling view to retrieve the rotation amount; there is nothing actually wrong with this but it forces the dialog to have additional information about its environment, which will limit its overall reusability).

However, if the TNumberText holding the rotation amount where overridden to set a value in the application (fRotationAmount, e.g.) when stopping editing, then the behavior could be attached to the button. In this case, the button would be set to want to become the target of the view. When the user clicks this button, the TNumberText would resign its target, which would cause it to stop editing, which in turn would cause it to update the application value. The button would then be free to post a command using this value.

Finally, we can take this one step further, and change the default event number of the button from mButtonHit to some application defined event (mRotate, e.g. ). We could then attach a behavior to the application that looks for the mRotate event and creates the appropriate command. This would allow us the flexibility of generating the mRotate command in multiple places in our interface, and handling them all identically. (Remember that the dialog we are discussing is modeless; this would not work in a modal dialog as it requires the event number of the default button to be mDismiss).

Once you understand how they function, TDialogBehaviors provide a simple, generic means of handling a common user interface problem. By carefully using them in cooperation with other built-in mechanisms, powerful interfaces can be designed with a minimum of coding. They can be used with modeless as well as modal dialogs, giving you complete freedom in designing your interface.

 

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.