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The Data Browser GetDataBrowserUserState API

Q: I am using GetDataBrowserUserState so that I can write my DataBrowser control's user state out to disk. (The user state is information about user customizable settings in the control, such as column widths and orderings.) I tried to call CFDataGetLength on the CFDataRef returned by GetDataBrowserUserState, but this resulted in a crash with "EXC_BAD_ACCESS" on Mac OS X. What am I doing wrong?

A: Unfortunately, the prototype for GetDataBrowserUserState (in Mac OS X 10.2.x and previous) is incorrect; GetDataBrowserUserState does not pass back a CFDataRef, it passes back a CFDictionaryRef.

You can use CFPropertyListyCreateXMLData to convert the CFDictionaryRef into a CFDataRef, thereby making it possible to call CFDataGetLength on the result.

For example:



Listing 1. 


CFDataRef state = NULL;
OSStatus err;

ControlRef browser = GetDataBrowserFromWindow(window);
err = GetDataBrowserUserState(browser, &state);

// check that the CFType of state is indeed a CFDictionaryRef
if ((noErr == err) && (CFGetTypeID(state) == CFDictionaryGetTypeID()))
{
  CFDataRef temp = NULL;
  CFIndex index;

  if (state != NULL) // defensive CoreFoundation error checking
  {
    temp = CFPropertyListCreateXMLData(NULL, (CFPropertyListRef)state);
    if (temp != NULL) // defensive CoreFoundation error checking
    {
      index = CFDataGetLength(temp); // length in bytes
      CFRelease(temp); // we created it, we need to release it
    }
  }
}
// The HIToolbox convention is to release references that were
// obtained using api that have "Copy" or "Create" in their names, but
// the DataBrowser api was written before the convention was adopted.
// You must release the item returned by GetDataBrowserUserState.
CFRelease(state);


[Jul 22, 2003]

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