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Dec 97 - Macintosh Q and A

Volume Number: 13 (1997)
Issue Number: 12
Column Tag: develop

Macintosh Q & A

by Apple Developer Support Center

White Backgrounds for Dialog editText Items

Q. I would like to have a colored background for my dialog box but I would like the TextEdit fields in my dialog box to be white. Is this possible to do? Is there some sample code available?

A. Generally speaking, this coloring is achieved via resources, not code. In addition to the dctb' resource, you need to create an 'ictb' resource.

To download a sample of an application using this kind of resource go to

The 'ictb' resource is documented on page 6-76 and starting again on page 6-158 of Inside Macintosh: Macintosh Toolbox Essentials. The best way I know of to create and edit 'ictb' resources is with Resorcerer, but you can also create them with a '.r' file compiled by either MPW's Rez or the Metrowerks CodeWarrior equivalent.

Here are some references to web sites for the aforementioned tools:

ETO (incl. Rez):

If this response has failed to adequately address a question or has raised more questions than it answered, please feel free to let us know and we'll try again.

Pete Gontier

OTScheduleDeferredTask When Task Running

Q. What happens when you use OTScheduleDeferredTask to schedule a task that is running?

A. The "Open Transport Client Note" mentions that OTScheduleDeferredTask returns false when you attempt to schedule a task that is already scheduled, but it doesn't say anything about what happens if the task is running. It turns out that a task that is running is not consider to be scheduled, so OTScheduleDeferredTask will successfully reschedule it.

Quinn "The Eskimo!"

Gestalt Values for Recent Macintosh Models

Q. What are the 'mach' gestalt values for the recent Macintosh models?

A. Recently, we announced the following new Macintosh models:

PowerBook 2400

The following list includes the 'mach' gestalt selectors for these and other Macintosh systems which are not included in the Gestalt.h header file which is part of the "Universal Interfaces 2.1 in MPW Latest" on ETO #22.

  • gestaltPerforma5300 = 41; { Macintosh Performa 53xx }
  • gestaltPowerMac5260 = 41; { Power Macintosh 5260/100 }
  • gestaltPerforma6300 = 42; { Macintosh Performa 63xx, except 6360 }
  • gestaltPerforma6360 = 58; { Performa 6360 }
  • gestaltPerforma6400 = 58; { Performa 6400 }
  • gestaltPowerMac9600 = 67; { Power Macintosh 9600
  • gestaltPowerMac7600 = 68; { Power Macintosh 7600 }
  • gestaltPowerMac8600 = 69; { Power Macintosh 8600 }
  • gestaltPowerMac5400 = 74; { Power Macintosh 5400/120}
  • gestaltMacLC580 = 99; { Macintosh LC 580 }
  • gestaltPerforma580 = 99; { Macintosh Performa 580 }
  • gestaltPowerMacLC475 = 104; { Mac LC 475 & PPC Processor Upgrade Card }
  • gestaltPowerMacPerforma47x = 104; { Performa 47x & PPC Proc Upgrade Card }
  • gestaltPowerMacLC575 = 105; { Mac LC 575 & PPC Processor Upgrade Card }
  • gestaltPowerMacPerforma57x = 105; { Performa 57x & PPC Proc Upgrade Card }
  • gestaltPowerMacQuadra630 = 106; { Quadra 630 & PPC Processor Upgrade Card }
  • gestaltPowerMacLC630 = 106; { Mac LC 630 & PPC Processor Upgrade Card }
  • gestaltPowerMac7300 = 109; { Power Macintosh 7300 }
  • gestaltPowerMacQuadra700 = 116; { Quadra 700 & Power PC Upgrade Card }
  • gestaltPowerMacQuadra900 = 117; { Quadra 900 & Power PC Upgrade Card }
  • gestaltPowerMacQuadra950 = 118; { Quadra 950 & Power PC Upgrade Card }
  • gestaltPowerMacCentris610 = 119; { Centris 610 & Power PC Upgrade Card }
  • gestaltPowerMacCentris650 = 120; { Centris 650 & Power PC Upgrade Card }
  • gestaltPowerMacQuadra610 = 121; { Quadra 610 & Power PC Upgrade Card }
  • gestaltPowerMacQuadra650 = 122; { Quadra 650 & Power PC Upgrade Card }
  • gestaltPowerMacQuadra800 = 123; { Quadra 800 & Power PC Upgrade Card }
  • gestaltPowerBook3400 = 306; { Macintosh PowerBook 3400 }
  • gestaltPowerBook2400 = 307; { Macintosh PowerBook 2400 }
  • gestaltPowerBook1400 = 310; { Macintosh PowerBook 1400 }
  • gestaltPowerMac5500 = 512; { Power Macintosh 5500 }
  • gestalt20thAnnivMac = 512; { Twentieth Anniversary Macintosh }
  • gestaltPowerMac5500 = 512; { Power Macintosh 5500 }
  • gestaltPowerMac6500 = 513; { Power Macintosh 6500 }
  • gestaltPowerMac4400 = 515; { Power Macintosh 4400 }

Note: To distinguish the Twentieth Anniversary Macintosh from the Power Macintosh 5500, make a secondary Gestalt selector call to the selector 'bxid'. The response for a Twentieth Anniversary Macintosh will be 0x0000302B

Rich Kubota

Find Desktop Folder

Q. The General control panel (GCP) in 7.6, 7.6.1 and 8.0 has the document options: Last folder, Application set folder, and Documents folder. How can my application determine where this folder is?

A. The General control panel (GCP) patches FindFolder so it will return the correct document folder given the current GCP options. Pass FindFolder a folderType of 'docs'. One quick note: Because the GCP patches FindFolder, the createFolder option doesn't work. If the folder doesn't exist you won't get an error and it won't be created. You have to write code to determine if the folder actually exist: if it doesn't, you'll have to create it yourself.

George Warner


Q. When I am debugging my application MemError() always returns noErr. What's wrong with MemError()?

A. Nothing, if you are debugging your application with a high level debugger. High level debuggers often call Memory Manager routines while stepping through your code. When a Memory Manager routine is called, it sets MemError() and in this case, the debugger's memory request was successful (it returned noErr) and cleared your application's MemError() result.

The solution to this problem is often just to not step over Memory Manager calls and the call to MemError(). If you put a break point just after the MemError() call, you usually get the correct error -- the one your application would see if it wasn't running in the debugger.

The other option is to use a low level debugger such as MacsBug to debug your memory allocation problems.

As a general rule your application should check the value of the handle or pointer returned by NewHandle, NewPtr, etc: and if it is nil, you should call MemError() for an error number. Just calling MemError() without checking the value of the handle/pointer is not a good idea.

Mark Cookson


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