需求：在固定宽度内，返回一个字符串需要显示的每行字符串
思路：Foundation框架并没有提供快相关API来解决这个问题，但是CoreText有，因为可能基础的应用CoreText应用不多，这里给出个sample，有兴趣的可以研究下：
#import "NSString+Lines.h"
#import <CoreText/CoreText.h>
@implementation NSString (Lines)
- (NSArray *)getSeparatedLinesWithFont:(UIFont *)font width:(CGFloat)width {
CTFontRef myFont = CTFontCreateWithName((__bridge CFStringRef)([font fontName]), [font pointSize], NULL);
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:self];
[attStr addAttribute:(NSString *)kCTFontAttributeName value:(__bridge id)myFont range:NSMakeRange(0, attStr.length)];
CTFramesetterRef frameSetter = CTFramesetterCreateWithAttributedString((__bridge CFAttributedStringRef)attStr);
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, CGRectMake(0, 0, width, 100000));
CTFrameRef frame = CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, 0), path, NULL);
NSArray *lines = (__bridge NSArray *)CTFrameGetLines(frame);
NSMutableArray *linesArray = [[NSMutableArray alloc]init];
for (id line in lines)
{
CTLineRef lineRef = (__bridge CTLineRef )line;
CFRange lineRange = CTLineGetStringRange(lineRef);
NSRange range = NSMakeRange(lineRange.location, lineRange.length);
NSString *lineString = [self substringWithRange:range];
[linesArray addObject:lineString];
}
return (NSArray *)linesArray;
}
@end
