Create a re-sizable array of CGPoints in objective-c

Question

Hi I am trying to create a re-sizable array of CGPoints in objective-c. I've have looked into using NSMutableArray however it doesnt seem to allow resizing. Is there something else I can use?

thank you

Answer 1

NSMutableArray is for objects. For plain old datatypes, use NSMutableData and good old pointer typecasts. It's a resizable unstructured memory buffer, just what you need for a vector of PODs. As for static type safety, Objective C does not give you any of that anyway.

EDIT:

Creating a mutable data object with an initial size n CGPoint structs:

NSMutableData *Data = [NSMutableData dataWithLength: n*sizeof(CGPoint)];

Placing a CGPoint pt into the buffer at the i-th position:

CGPoint pt;
NSRange r = {i*sizeof(CGPoint), sizeof(CGPoint)};
[Data replaceBytesInRange: r withBytes:&pt];

Retrieving a CGPoint from the i-th position into pt:

CGPoint pt;
NSRange r = {i*sizeof(CGPoint), sizeof(CGPoint)};
[Data getBytes: &pt range:r];

Growing the array by n objects:

[Data increaseLengthBy:n*sizeof(CGPoint)];

Hope that covers it. See the NSMutableData reference, and keep in mind that all NSData methods apply to it.

Answer 2

Use an NSMutableArray, but just box your CGPoint structs in NSValue objects. Example:

CGPoint myPoint = {0,0};
CGPoint anotherPoint = {42, 69};

NSMutableArray * array = [NSMutableArray array];
[array addObject:[NSValue valueWithCGPoint:myPoint]];
[array addObject:[NSValue valueWithCGPoint:anotherPoint]];

CGPoint retrievedPoint = [[array objectAtIndex:0] CGPointValue];

Note that the +valueWithCGPoint: and CGPointValue methods are only available on the iPhone. However if you need this for the Mac, there are similar methods for dealing with NSPoints, and it's trivial to convert a CGPoint to an NSPoint (you can cast or use NSPointFromCGPoint()).