在等待最终解决方案的同时，我研究了 RTLabel 和 TTTAttributedLabel，并按照史蒂夫的建议制作了一个简单的类来在 CALayer 上绘制文本。希望它有所帮助，请不要犹豫指出我犯的任何错误。
CustomTextLayer.h
#import <QuartzCore/QuartzCore.h>
@interface CustomTextLayer : CALayer {
NSString *_text;
UIColor *_textColor;
NSString *_font;
float _fontSize;
UIColor *_strokeColor;
float _strokeWidth;
CTTextAlignment _textAlignment;
int _lineBreakMode;
float _suggestHeight;
}
-(float) suggestedHeightForWidth:(float) width;
@property (nonatomic, retain) NSString *text;
@property (nonatomic, retain) UIColor *textColor;
@property (nonatomic, retain) NSString *font;
@property (nonatomic, assign) float fontSize;
@property (nonatomic, retain) UIColor *strokeColor;
@property (nonatomic, assign) float strokeWidth;
@property (nonatomic, assign) CTTextAlignment textAlignment;
@end
CustomTextLayer.m
#import <CoreText/CoreText.h>
#import "CustomTextLayer.h"
@implementation CustomTextLayer
@synthesize text = _text, textColor = _textColor;
@synthesize font = _font, fontSize = _fontSize;
@synthesize strokeColor = _strokeColor, strokeWidth = _strokeWidth;
@synthesize textAlignment = _textAlignment;
-(id) init {
if (self = [super init]) {
_text = @"";
_textColor = [UIColor blackColor];
_font = @"Helvetica";
_fontSize = 12;
_strokeColor = [UIColor whiteColor];
_strokeWidth = 0.0;
_textAlignment = kCTLeftTextAlignment;
_lineBreakMode = kCTLineBreakByWordWrapping;
}
return self;
}
-(void) dealloc {
[_text release];
[_textColor release];
[_font release];
[_strokeColor release];
[super dealloc];
}
-(void) setText:(NSString *)text {
[_text release];
_text = [text retain];
[self setNeedsDisplay];
}
-(void) setTextColor:(UIColor *)textColor {
[_textColor release];
_textColor = [textColor retain];
[self setNeedsDisplay];
}
-(void) setFont:(NSString *)font {
[_font release];
_font = [font retain];
[self setNeedsDisplay];
}
-(void) setFontSize:(float)fontSize {
_fontSize = fontSize;
[self setNeedsDisplay];
}
-(void) setStrokeColor:(UIColor *)strokeColor {
[_strokeColor release];
_strokeColor = strokeColor;
[self setNeedsDisplay];
}
-(void) setStrokeWidth:(float)strokeWidth {
_strokeWidth = 0 ? (strokeWidth < 0) : (-1 * strokeWidth);
[self setNeedsDisplay];
}
-(void) setTextAlignment:(CTTextAlignment)textAlignment {
_textAlignment = textAlignment;
[self setNeedsDisplay];
}
-(void) setFrame:(CGRect)frame {
[super setFrame: frame];
[self setNeedsDisplay];
}
-(float) suggestedHeightForWidth:(float) width {
CTFontRef fontRef = CTFontCreateWithName((CFStringRef)_font, _fontSize, NULL);
CTParagraphStyleSetting paragraphStyles[2] = {
{.spec = kCTParagraphStyleSpecifierLineBreakMode, .valueSize = sizeof(CTLineBreakMode), .value = (const void *) &_lineBreakMode},
{.spec = kCTParagraphStyleSpecifierAlignment, .valueSize = sizeof(CTTextAlignment), .value = (const void *) &_textAlignment}
};
CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(paragraphStyles, 2);
NSDictionary *attrDict = [[NSDictionary alloc] initWithObjectsAndKeys:(id)fontRef, (NSString *)kCTFontAttributeName, (id)_textColor.CGColor, (NSString *)(kCTForegroundColorAttributeName), (id)_strokeColor.CGColor, (NSString *)(kCTStrokeColorAttributeName), (id)[NSNumber numberWithFloat: _strokeWidth], (NSString *)(kCTStrokeWidthAttributeName), (id)paragraphStyle, (NSString *)(kCTParagraphStyleAttributeName), nil];
CFRelease(fontRef);
CFRelease(paragraphStyle);
NSAttributedString *attrStr = [[NSAttributedString alloc] initWithString:_text attributes: attrDict];
// Determine suggested frame height
CFRange textRange = CFRangeMake(0, [attrStr length]);
CGSize constraint = CGSizeMake(width, 9999);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrStr);
CGSize textSize = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, textRange, NULL, constraint, NULL);
textSize = CGSizeMake(ceilf(textSize.width), ceilf(textSize.height));
[attrDict release];
[attrStr release];
return textSize.height;
}
-(void) renderText:(CGContextRef)ctx {
CGContextSetTextMatrix(ctx, CGAffineTransformIdentity);
CGContextTranslateCTM(ctx, 0, self.bounds.size.height);
CGContextScaleCTM(ctx, 1.0, -1.0);
CTFontRef fontRef = CTFontCreateWithName((CFStringRef)_font, _fontSize, NULL);
CTParagraphStyleSetting paragraphStyles[2] = {
{.spec = kCTParagraphStyleSpecifierLineBreakMode, .valueSize = sizeof(CTLineBreakMode), .value = (const void *) &_lineBreakMode},
{.spec = kCTParagraphStyleSpecifierAlignment, .valueSize = sizeof(CTTextAlignment), .value = (const void *) &_textAlignment}
};
CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(paragraphStyles, 2);
NSDictionary *attrDict = [[NSDictionary alloc] initWithObjectsAndKeys:(id)fontRef, (NSString *)kCTFontAttributeName, (id)_textColor.CGColor, (NSString *)(kCTForegroundColorAttributeName), (id)_strokeColor.CGColor, (NSString *)(kCTStrokeColorAttributeName), (id)[NSNumber numberWithFloat: _strokeWidth], (NSString *)(kCTStrokeWidthAttributeName), (id)paragraphStyle, (NSString *)(kCTParagraphStyleAttributeName), nil];
CFRelease(fontRef);
CFRelease(paragraphStyle);
NSAttributedString *attrStr = [[NSAttributedString alloc] initWithString:_text attributes: attrDict];
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, self.bounds);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrStr);
CFRange textRange = CFRangeMake(0, [attrStr length]);
CTFrameRef frame = CTFramesetterCreateFrame(framesetter, textRange, path, NULL);
CFArrayRef lines = CTFrameGetLines(frame);
NSInteger numberOfLines = CFArrayGetCount(lines);
CGPoint lineOrigins[numberOfLines];
CTFrameGetLineOrigins(frame, CFRangeMake(0, numberOfLines), lineOrigins);
for (CFIndex lineIndex = 0; lineIndex < numberOfLines; lineIndex++) {
CGPoint lineOrigin = lineOrigins[lineIndex];
CGContextSetTextPosition(ctx, lineOrigin.x, lineOrigin.y);
CTLineRef line = CFArrayGetValueAtIndex(lines, lineIndex);
if (lineIndex == numberOfLines - 1) {
CFRange lastLineRange = CTLineGetStringRange(line);
if (!(lastLineRange.length == 0 && lastLineRange.location == 0) && lastLineRange.location + lastLineRange.length < textRange.location + textRange.length) {
NSUInteger truncationAttributePosition = lastLineRange.location;
CTLineTruncationType truncationType;
if (numberOfLines != 1) {
truncationType = kCTLineTruncationEnd;
truncationAttributePosition += (lastLineRange.length - 1);
}
NSAttributedString *tokenString = [[NSAttributedString alloc] initWithString:@"\u2026" attributes:attrDict];
CTLineRef truncationToken = CTLineCreateWithAttributedString((CFAttributedStringRef)tokenString);
NSMutableAttributedString *truncationString = [[attrStr attributedSubstringFromRange: NSMakeRange(lastLineRange.location, lastLineRange.length)] mutableCopy];
if (lastLineRange.length > 0) {
unichar lastCharacter = [[truncationString string] characterAtIndex: lastLineRange.length - 1];
if ([[NSCharacterSet newlineCharacterSet] characterIsMember:lastCharacter]) {
[truncationString deleteCharactersInRange:NSMakeRange(lastLineRange.length - 1, 1)];
}
}
[truncationString appendAttributedString: tokenString];
CTLineRef truncationLine = CTLineCreateWithAttributedString((CFAttributedStringRef) truncationString);
CTLineRef truncatedLine = CTLineCreateTruncatedLine(truncationLine, self.bounds.size.width, truncationType, truncationToken);
if (!truncatedLine) {
// If the line is not as wide as the truncationToken, truncatedLine is NULL
truncatedLine = CFRetain(truncationToken);
}
CTLineDraw(truncatedLine, ctx);
CFRelease(truncatedLine);
CFRelease(truncationLine);
CFRelease(truncationToken);
} else {
CTLineDraw(line, ctx);
}
} else {
CTLineDraw(line, ctx);
}
}
[attrStr release];
[attrDict release];
CFRelease(path);
CFRelease(frame);
CFRelease(framesetter);
}
-(void) drawInContext:(CGContextRef)ctx {
[super drawInContext: ctx];
[self renderText: ctx];
}
@end
