2

I want to make an array of structs of which the size is known only at runtime

NSMutableArray *styleSettingsArray = [NSMutableArray array];

NSString *fontAlignmentAttribute = [element attributeNamed:@"TextAlignment"];
if(fontAlignmentAttribute)
{
    CTTextAlignment alignment = [self getTextAlignment:fontAlignmentAttribute];
    CTParagraphStyleSetting styleSetting = {kCTParagraphStyleSpecifierAlignment, sizeof(CTTextAlignment), &alignment};
    [styleSettingsArray addObject:[NSValue valueWithBytes:&styleSettings objCType:@encode(CTParagraphStyleSetting)]];
}

// other posible attributes

CTParagraphStyleRef paragraphStyleRef = CTParagraphStyleCreate((__bridge const CTParagraphStyleSetting *)(styleSettingsArray), [styleSettingsArray count]);
[dictionary setObject:(__bridge id)(paragraphStyleRef) forKey:(NSString*)kCTParagraphStyleAttributeName];
CFRelease(paragraphStyleRef);

This code does not work.

EDIT:

CTParagraphStyleCreate takes a pointer to an array of CTParagraphStyleSetting, such as

CTParagraphStyleSetting styleSettings[] = {
    { kCTParagraphStyleSpecifierAlignment, sizeof(CTTextAlignment), alignment},
    {...},
    {...}
};

How can I allocate this array, and add stuff to it without knowing how much stuff will be in it ? (how do I use malloc ?)

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6
  • It works when I use CTParagraphStyleSetting styleSettings[] = {{kCTParagraphStyleSpecifierAlignment,sizeof(CTTextAlignment), alignment}}; , but when i pass a NSMutableArray to CTParagraphStyleCreate, the attributes don't get applied to the text Commented Mar 14, 2013 at 9:26
  • There was an answer mentioning opaque types, not sure why it is removed. If you look at CTParagraphStyleCreate documentation, there's a reference to CTParagraphStyleSetting typedef, you can't just cast NSArray to CTParagraphStyleSetting. Commented Mar 14, 2013 at 9:45
  • Yeah.Idk what happened with your answer. I saw it, tried to add a comment (the edit). I looked at the docs, but what I can't figure out is what to make instead of a NSArray Commented Mar 14, 2013 at 9:48
  • @A-Live I removed the answer (actually edited it now) as it was wrong. Commented Mar 14, 2013 at 9:50
  • just like @trojanfoe said at the original answer, you'll want to use special method to create opaque type variables. Googling for CTParagraphStyleCreate gave me an example in seconds :) Commented Mar 14, 2013 at 10:01

2 Answers 2

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2

You cannot mix Objective-C or Core Foundation collections with plain C arrays in this way. Also as you have found out you need to wrap those CTParagraphStyleSetting structs in NSNumber objects in order to store them. What a mess.

The approach I would take would be to do 2-passes; the first to determine how many attributes you have and the second to generate those attributes.

  1. Iterate over your conditions to find out how many attributes there are
  2. Allocate a C array (see malloc()).
  3. Iterate over your conditions and store the attributes in the dynamic array.
  4. Use the array to create the style.
  5. Free the array (see free()).

NOTE I have edited this answer as my previous answer was way off.

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2 Comments

Core Foundation Design Concepts: Opaque Types
i'll just refresh my c a bit and come back to you on this one.
1

To avoid having to collect the number of attributes and then create them in a second pass I suggest to use NSMutableData instead of a plain C array or malloc. This style would allow you to use your existing code with only minimal changes:

NSMutableData *styleSettingsArray = [NSMutableData array];

NSString *fontAlignmentAttribute = [element attributeNamed:@"TextAlignment"];
CTTextAlignment alignment;
if (fontAlignmentAttribute)
{
    alignment = [self getTextAlignment:fontAlignmentAttribute];
    CTParagraphStyleSetting styleSetting = { kCTParagraphStyleSpecifierAlignment, sizeof(CTTextAlignment), &alignment};
    [styleSettingsArray appendBytes:&styleSetting length:sizeof(styleSetting)];
}

// other posible attributes
CTParagraphStyleRef paragraphStyleRef = CTParagraphStyleCreate([styleSettingsArray bytes], [styleSettingsArray length] / sizeof(CTParagraphStyleSetting));

Edit: Please note the extension of the lifetime of the alignment variable, compared to your code. This is necessary because it is referenced after the block ends in which it was declared before.

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5 Comments

I don't think that is very attractive either; I don't see how Objective-C / Core Foundation classes can help with this problem that exists in any C API. If anything a C++ vector might prove the best solution, however that is out-of-scope.
@trojanfoe I'm not sure what kind of issue you see with this code but I think that it exactly solves the problem at hand: need of a C array that grows as needed. Plus it gives you automatic objc memory management (no need to free some malloced buffer).
My primary dislike is the conversion from native struct instances to arrays of bytes. It feels cumbersome. I'm not saying it won't work; simply that it's unattractive.
@trojanfoe To me it seems much more attractive than to 1) count the number of needed elements, 2) malloc a buffer, 3) copy the structs to the buffer and 4) free the buffer. It feels that this proposal makes the task much less complex, especially by avoiding the need for two passes.
Well each to his own then.

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