Manual Line Breaking

gistfile1.m

    CGContextRef context = UIGraphicsGetCurrentContext();
    
//    // Flip the coordinate system
//    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
//    CGContextTranslateCTM(context, 0, self.bounds.size.height);
//    CGContextScaleCTM(context, 1.0, -1.0);
    
    UIFont *customFont = [UIFont systemFontOfSize:20];
    
    CTFontRef font = CTFontCreateWithName((CFStringRef)customFont.fontName, 20, NULL);
    
    NSDictionary *attrs = @{(NSString *)kCTFontAttributeName: (__bridge id)font,
                            (NSString *)kCTForegroundColorAttributeName: (__bridge id)[UIColor blueColor].CGColor,
                            (NSString *)kCTUnderlineStyleAttributeName: @(NSUnderlineStyleSingle),
                            };
    
    // Make an attributed string
    NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:@"Hello CoreText!" attributes:attrs];
    CFAttributedStringRef attributedStringRef = (CFAttributedStringRef)attributedString;
    
    CTTypesetterRef typesetter = CTTypesetterCreateWithAttributedString(attributedStringRef);
    
    CFIndex start = 0;
    double width = CGRectGetWidth(self.bounds);
    double height = CGRectGetHeight(self.bounds);
    CFIndex stringLength = CFAttributedStringGetLength(attributedStringRef);
    CGPoint textPosition = CGPointMake(0, height);

    // this lineHeight may not equal customFont.lineHeight
    // if you need line gap, you should control it by yourself
    CGFloat lineHeight = CTFontGetAscent(font) + fabs(CTFontGetDescent(font)) + CTFontGetLeading(font);
    
    while (start<stringLength) {
        CFIndex count = CTTypesetterSuggestClusterBreak(typesetter, start, width);
        CTLineRef line = CTTypesetterCreateLine(typesetter, CFRangeMake(start, count));
        
        // Get the offset needed to center the line.
        float flush = 0.5; // 0,left; 0.5,center; 1,right
        double penOffset = CTLineGetPenOffsetForFlush(line, flush, width);
        
        // Move the given text drawing position by the calculated offset and draw the line.
        CGContextSetTextPosition(context, textPosition.x + penOffset, textPosition.y - lineHeight);
        CTLineDraw(line, context);
        
        start += count;
        textPosition.y -= lineHeight;
    }