Technical Q&A's

TB 22 - Drag Manager & the 600 (procNotFound) Error (21-August-96)

Q Sometimes my application's calls to the Drag Manager fail with a -600 (procNotFound) error. This is not one of the errors listed for these calls. What's up?

A There are three known common causes of this error:

The use of high-level debuggers. Since Drag Manager interacts heavily with Process Manager, as does the typical high-level debugger, conflicts inevitably develop. There's no work-around for this problem except to ask your debugger vendor to improve its behavior when debugging Drag Manager code. If your code is encountering such a problem, it should run fine when the debugger is not involved.
Passing TrackDrag an EventRecord whose 'where' field is expressed in local coordinates. (This can also result in a crash, but sometimes simply results in a -600 error.) Such 'where' fields often point outside the window in which the drag originates.
Attempting to use the Drag Manager with Text Services Manager windows when the 'gestaltDragMgrFloatingWind' bit is not defined in the response to the 'gestaltDragMgrAttr' Gestalt selector. The value of this bit denotes whether a Drag Manager bug with TSM windows is fixed on the system under which your app is running.

In the second and third cases, Drag Manager has a hard time associating the source window with a process. Some operations can succeed even without a clear owning process, so Drag Manager limps along as best it can for a while in the hopes that it won't be asked to do anything which requires a ProcessSerialNumber. When it is, the operation fails.

-- Pete Gontier

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