TweetFollow Us on Twitter

Jun 97 - Macintosh Q and A

Volume Number: 13 (1997)
Issue Number: 6
Column Tag: develop

Macintosh Q&A

by Apple Developer Support Center

Q: When I used CopyBits to do a screen capture, the cursor isn't included. Why not?

A: CopyBits calls ShieldCursor to hide the cursor before it does its work. That's why you never see the cursor in your screen capture. The following code hides the cursor and decrements the cursor count in the low-memory global to fool CopyBits not to call ShieldCursor. Standard warning: Using low-memory globals is dangerous and is subject to future OS changes.

unsigned char   oldCrsrVis;
short           oldCrsrState;
      
// Hide the cursor.
oldCrsrVis = GetCrsrVis();
oldCrsrState = GetCrsrState();
SetCrsrVis((unsigned char) 0);
SetCrsrState(oldCrsrState - 1);   
// Do the screen capture.
CopyBits(...)
      
// Restore the old cursor.
SetCrsrState(oldCrsrState);
SetCrsrVis(oldCrsrVis);

You should define the cursor functions as follows:

enum {
   CrsrVis = 0x8CC,      // Cursor visible? [byte]
   CrsrState = 0x8D0      // Cursor nesting level [word]
};
   
void SetCrsrVis(unsigned char cursorVisible)   
{
   *(unsigned char*)CrsrVis = cursorVisible;
}

unsigned char GetCrsrVis(void)
{
   return ( *(unsigned char*)CrsrVis );
}   

short GetCrsrState(void)
{
   return ( *(unsigned char*)CrsrState );
}   

void SetCrsrState(short val)
{
   *(unsigned char*)CrsrState = val;
}

Q: How can I determine whether the cursor is hidden?

A: Currently the best way to determine this is to use a low-memory global that has been removed from LowMem.h. The reason it has been removed is that a future operating system may handle it differently.

Using low-memory globals has never really been sanctioned, though they were documented in older interface files. The Universal Interfaces were designed to make way for future operating systems; access to some low-memory globals was provided through accessor functions for safety, while access to others was removed.

The global you want, CrsrVis, is a byte-sized flag that tells whether the cursor is hidden. It was defined in an older interface file like this:

enum {
   CrsrVis = 0x8CC,   // Cursor visible? [byte]
};

You can simply check this global to see if the cursor is hidden. As always, the direct use of low-memory globals is not recommended and will probably cause your code to break in the future.


Q: I want to support dragging from my application to the Trash without having the Finder create a clipping file inside the Trash. I tried several options but they all failed. Is this possible?

A: There is no good way to prevent a clipping file from being created in the Trash, or to prevent the "zoomback" animation that signals a failed drag. The problem is that the Finder treats the Trash like a folder; the drag succeeds or fails according to the user's supposed intent with respect to a folder.

In our opinion, however, this is good, since it's consistent with the Trash metaphor. When the user drags an icon from a Finder window into the Trash, she expects the Trash to get fat so that she can later change her mind, open the Trash, and drag the icon back out. Creating a clipping file in the Trash merely extends the metaphor. The only problem this might cause is that the user ought to be able to reverse her decision and drag the clipping back into the application. If your application doesn't already support this action, you may have some work ahead.

We realize that other applications manage to avoid making the Trash fat. This is, in our opinion, a Bad Thing. A Hack. Wrong. Nevertheless, if you still feel you need to avoid making the Trash fat, it might be possible to do so. It would probably involve creating a file via flavorTypePromiseHFS, then deleting it before the Finder has a chance to make the Trash fat. Unfortunately, since this involves "fooling" the Finder, it isn't likely to work for future versions of the Finder even if it does work today.

In short, this is not recommended.


Q: When my application calls TrackDrag, it crashes in low memory at an illegal instruction. The MacsBug stack crawl doesn't produce any useful information. I've stared and stared at my application's calls to the Drag Manager, and all the parameters appear to be valid. My drag tracking handler is never called, incidentally. If I take all calls to the Drag Manager out of my application, it runs just fine. I've been investigating this crash for two months. Why is life so cruel?

A: You've unearthed a really ugly problem. The Drag Manager thinks the drag originated in the Finder, and makes some fatal assumptions based on that.

Early versions of the Drag Manager did not enjoy the benefits of a drag-enabled Finder, so the Drag Manager plays a little fast and loose with the Finder's jump table. Yes, that means what it sounds like: the Drag Manager calls the Finder routines through its jump table.

The even more interesting story concerns the method by which the Drag Manager decides that the current application is the Finder. When TrackDrag is called, the Drag Manager determines whether the drag originates in any of the windows in the window list of the current process. If not, the Drag Manager determines whether the drag originates in any Finder window. Since the desktop is a "window" for these purposes, there's a large area that qualifies.

Once the Drag Manager has decided the drag originated in a Finder window, it assumes that the Finder is the current process. (This is the fatal mistake.) Once this assumption is made, the next thing for the Drag Manager to do to coax the Finder into exhibiting the correct drag behavior is call an entry in whatever jump table can be found by offsetting the current value of register A5. This is valid if the Finder is the current process, but of course if the current process is your application instead, things go terribly astray: The Drag Manager calls a jump table entry in your application, thinking it's the Finder, and your application's routine doesn't do the same thing that the Finder routine would. Any number of spectacular effects can result.

"Now wait a minute," you're thinking, "the drag originated in one of my application's windows; how is this stuff about the Finder relevant?" The answer is in the event record you're passing to TrackDrag. An event record is supposed to contain a where field expressed in global coordinates. However, the where field your application is passing is in local coordinates. How did this happen? Well, that depends on your application, but often it can result from an application frameworks (like PowerPlant, MacApp, or THINK Class Library) modifying the event record before passing it to your code. There's no language-level way to specify that the record has been modified, so the compiler doesn't warn you. (Honestly, this is Not Your Fault.)

Your code blithely calls TrackDrag with what it assumes is a valid event record but is not. TrackDrag interprets the where field, which is actually in local coordinates, as global coordinates. This point is somewhere up and to the left of where your application expects, and quite often it's in the desktop, which as we said above is considered a Finder window for these purposes. The Drag Manager reacts by going through its ritual for drags originating in Finder windows and eventually crashes after calling some odd routine in your application, as described above.

To solve this problem, simply call LocalToGlobal on the where field of the event record before calling TrackDrag.


Q: When I drag from my application into a Finder window, the system crashes. I notice the Finder uses a windowKind value of 20 for its windows, and so does my application. When my application avoids windowKind 20, everything's hunky-dory. What's going on?

A: Through the Drag Manager, the Finder has gotten access to the windows in your application's window list (specifically, by using undocumented calls to obtain the source window of a drag). If your window's windowKind field is 20, the Finder assumes the window is one of its own (as opposed to a driver window, whose windowKind would be negative, or a dialog window, whose windowKind would be 2, and so on). The Finder grabs the value in the window's refCon field and type-casts it to a pointer to a C++ object in the Finder's heap. I think you can see where this is going: when the Finder attempts to dereference the pointer, many fascinating crashing behaviors can result.

The upshot of this Finder bug is that your application should not use windowKind values of 20.

 
AAPL
$102.99
Apple Inc.
+0.00
MSFT
$44.38
Microsoft Corpora
+0.00
GOOG
$532.71
Google Inc.
+0.00

MacTech Search:
Community Search:

Software Updates via MacUpdate

jAlbum Pro 12.2.4 - Organize your digita...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code!... Read more
jAlbum 12.2.4 - Create custom photo gall...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results Simply drag and drop photos into groups, choose a design... Read more
ExpanDrive 4.1.7 - Access remote files o...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Evernote 5.6.2 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
OmniOutliner 4.1.3 - Organize your ideas...
OmniOutliner is a flexible program for creating, collecting, and organizing information. Give your creativity a kick start by using an application that's actually designed to help you think. It's... Read more
BBEdit 11.0 - Powerful text and HTML edi...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
Apple Security Update 2014-005 - For OS...
Apple Security Update is recommended for all users and improves the security of Mac OS X. For information on the security content of this update, please visit this website: http://support.apple.com/... Read more
EyeTV 3.6.6 - Watch and record TV on you...
EyeTV brings a rich TV experience to your Mac. Watch live TV on your Mac. Pause, rewind, and record whenever you want. EyeTV gives you powerful control over what you watch and how you watch it. Put... Read more
RapidWeaver 6.0 - 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
NTFS 12.0.39 - Provides full read and wr...
Paragon NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS, providing full read and write access to... Read more

Latest Forum Discussions

See All

Jam Messenger Review
Jam Messenger Review By Jennifer Allen on October 23rd, 2014 Our Rating: :: SIMPLE MESSAGINGiPhone App - Designed for the iPhone, compatible with the iPad Want a very quick way to send push-based messages? Jam Messenger is basic... | Read more »
Felllice (Games)
Felllice 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: EXCLUSIVE PRICE DROP! 50% OFF FOR A LIMITED TIME! EAT EAT EAT AND GROW ! | Read more »
The Arrow Game: by Grazie Media (Games)
The Arrow Game: by Grazie Media 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Guide a flying arrow through skyscrapers and city streets to hit a distant target. Experience an endless... | Read more »
Worldly (Games)
Worldly 1.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2 (iTunes) Description: | Read more »
Money Pro - EASY! Bills, Budgets and Acc...
Money Pro - EASY! Bills, Budgets and Accounts w/ Sync 1.0 Device: iOS Universal Category: Finance Price: $4.99, Version: 1.0 (iTunes) Description: Manage money like a pro. Money Pro is the next generation of Money app (over 2 million... | Read more »
Pro Strategy Football 2014 (Games)
Pro Strategy Football 2014 2014.141001 Device: iOS Universal Category: Games Price: $4.99, Version: 2014.141001 (iTunes) Description: Take the proven strategy of the PSF franchise and add in Casual Play, improved graphics and... | Read more »
Super Glyph Quest (Games)
Super Glyph Quest 1.01 Device: iOS Universal Category: Games Price: $2.99, Version: 1.01 (iTunes) Description: Adventure is back Questers! Combine elemental glyphs together to cast powerful spells and vanquish adorable monsters in... | Read more »
Fighting Fantasy: Caverns of the Snow Wi...
Fighting Fantasy: Caverns of the Snow Witch 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: Travel to Northern Allansia’s perilous Icefinger Mountains to defeat the wicked Snow Witch in this... | Read more »
Star Warfare 2: Payback Review
Star Warfare 2: Payback Review By Blake Grundman on October 22nd, 2014 Our Rating: :: ONE-TRICK PONYUniversal App - Designed for iPhone and iPad Unfortunately, it doesn’t take long for Star Warfare 2’s free-firing fun to turn into... | Read more »
TinType by Hipstamatic (Photography)
TinType by Hipstamatic 1.0 Device: iOS iPhone Category: Photography Price: $.99, Version: 1.0 (iTunes) Description: Create hauntingly beautiful, soul capturing portraits with TinType by Hipstamatic. Inspired by daguerreotypes,... | Read more »

Price Scanner via MacPrices.net

Save with Best Buy’s College Student Deals
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through November 1st. Anyone with a valid .EDU email address can take advantage... Read more
iPad Air 2 & iPad mini 3 Best Tablets Yet...
The new iPads turned out to be pretty much everything I’d been hoping for and more than I’d expected.”More” particularly in terms of a drinking-from-a-firehose choice of models and configurations,... Read more
Drafts 4 Reinvents iOS Productivity App
N Richland Hills, Texas based Agile Tortoise has announced the release of Drafts 4 for iPhone and iPad. Drafts is a quick capture note taking app with flexible output actions. Drafts 4 scales from... Read more
AT&T accepting preorders for new iPads fo...
AT&T Wireless is accepting preorders for the new iPad Air 2 and iPad mini 3, cellular models, for $100 off MSRP with a 2-year service agreement: - 16GB iPad Air 2 WiFi + Cellular: $529.99 - 64GB... Read more
Apple offering refurbished Mac Pros for up to...
The Apple Store is offering Apple Certified Refurbished 2013 Mac Pros for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Select MacBook Airs $100 off MSRP, free shipp...
B&H Photo has 2014 a couple of MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for... Read more
13-inch 2.5GHz MacBook Pro on sale for $100 o...
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
Strong iPhone, Mac And App Store Sales Drive...
Apple on Monday announced financial results for its fiscal 2014 fourth quarter ended September 27, 2014. The Company posted quarterly revenue of $42.1 billion and quarterly net profit of $8.5 billion... Read more
Apple Posts How-To For OS X Recovery
OS X 10.7 Lion and later include OS X Recovery. This feature includes all of the tools you need to reinstall OS X, repair your disk, and even restore from a Time Machine backup. OS X Recovery... Read more
Mac OS X Versions (Builds) Supported By Vario...
Apple Support has posted a handy resource explaining which Mac OS X versions (builds) originally shipped with or are available for your computer via retail discs, downloads, or Software Update. Apple... Read more

Jobs Board

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
*Apple* Solutions Consultant (ASC) - Apple (...
**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
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.