iOS Context 基础教程 （三）完整实现UILabel末尾 实现『省略号常看全文』显示

直接上代码，实现限制UIlabel最多显示行数，超出后显示 『。。。全文』效果实现：

细节还待优化，给需要的人参考吧

//  BDHKLabelAttribute.h

#import <UIKit/UIKit.h>

/*!
@enum BDHKVerticalTextAlignment
@abstract 垂直方式
*/
typedef NS_ENUM(NSInteger, BDHKVerticalTextAlignment) {
/*!
@abstract 顶部
*/
BDHKVerticalTextAlignmentTop,

/*!
@abstract 居中
*/
BDHKVerticalTextAlignmentMiddle,

/*!
@abstract 底部
*/
BDHKVerticalTextAlignmentBottom
};

@interface BDHKLabelAttribute : UILabel

/*!
@property verticalTextAlignment
@abstract 上下对齐方式
*/
@property (nonatomic, assign) BDHKVerticalTextAlignment verticalTextAlignment;

/*!
@property linesSpace
@abstract 行间距
*/
@property (nonatomic, assign) CGFloat linesSpace;

/*!
@property margin
@abstract 边距
*/
@property (nonatomic, assign) UIEdgeInsets margin;

/*!
@property lastLineRightIndent
@abstract 尾行右缩进
*/
//@property (nonatomic, assign) CGFloat lastLineRightIndent;

/*!
@property truncationEndAttributedString
@abstract 尾行结束字符串
*/
@property (nonatomic, strong) NSAttributedString *truncationEndAttributedString;

/*!
@property linesSpace
@abstract 实际绘制的行数,当numberOfLines==0时
*/
@property (nonatomic, assign, readonly) NSInteger drawOfLines;

@end

@interface NSString(BDHKLabelAttribute)

/*!
@method sizeWithFont:width:linesSpace:numberOfLines:
@abstract 测量字符串所要的大小
@param font 字体
@param width 宽度
@param linesSpace 行高
@param numberOfLines 行数
*/
- (CGSize)sizeWithFont:(UIFont *)font width:(CGFloat)width linesSpace:(CGFloat)linesSpace numberOfLines:(NSInteger)numberOfLines;

@end

//  BDHKLabelAttribute.m

#import "BDHKLabelAttribute.h"
#import "UIView+BDHKUtil.h"
#import <CoreText/CoreText.h>

@interface BDHKLabelAttribute()

@property (nonatomic, copy) NSMutableAttributedString *attributedString;
@property (nonatomic, assign) BOOL isDisplay;
@property (nonatomic, assign) BOOL isText;

@end

@implementation BDHKLabelAttribute

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
_margin = UIEdgeInsetsZero;
_verticalTextAlignment = BDHKVerticalTextAlignmentTop;
_isDisplay = YES;
}
return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
_margin = UIEdgeInsetsZero;
_verticalTextAlignment = BDHKVerticalTextAlignmentTop;
_isDisplay = YES;
}
return self;
}

-(void)dealloc
{
_attributedString = nil;
_truncationEndAttributedString = nil;
}

- (void)drawTextInRect:(CGRect)rect
{
if (self.text.length == 0 && self.attributedText == nil) {
return;
}

if (_isDisplay) {
if (_isText) {
self.attributedString = [self attributedStringAddStyle:self.text];
}
else {
self.attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
}
_isDisplay = NO;
}

if (!_attributedString) {
return;
}

CGRect drawRect = CGRectMake(_margin.left, _margin.top, self.bounds.size.width - _margin.left - _margin.right, self.bounds.size.height - _margin.top - _margin.bottom);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)_attributedString);
CGMutablePathRef forecastPath = CGPathCreateMutable();
//CGPathAddRect(forecastPath, NULL ,self.bounds);
CGPathAddRect(forecastPath, NULL ,drawRect);
CTFrameRef forecastFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(0, 0), forecastPath , NULL);
CFArrayRef forecastLines = CTFrameGetLines(forecastFrame);
long forecastMaxLineNumber = (long)CFArrayGetCount(forecastLines);

//CGRect drawingRect = CGRectMake(0, 0, self.bounds.size.width, CGFLOAT_MAX);
CGRect drawingRect = CGRectMake(drawRect.origin.x, drawRect.origin.y, drawRect.size.width, 100000000);
CGMutablePathRef textpath = CGPathCreateMutable();
CGPathAddRect(textpath, NULL, drawingRect);
CTFrameRef textFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(0,0), textpath, NULL);
CFArrayRef textlines = CTFrameGetLines(textFrame);
long textMaxLineNumber = (long)CFArrayGetCount(textlines);

long minLinesNumber = MIN(forecastMaxLineNumber, textMaxLineNumber);
_drawOfLines = (int)(self.numberOfLines == 0 ? minLinesNumber : MIN(minLinesNumber, self.numberOfLines));

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetTextMatrix(context , CGAffineTransformIdentity);
CGContextTranslateCTM(context , 0 ,self.bounds.size.height);
CGContextScaleCTM(context, 1.0 ,-1.0);

CGPoint lineOrigins[_drawOfLines];
CTFrameGetLineOrigins(forecastFrame,CFRangeMake(0,_drawOfLines), lineOrigins);

for(int lineIndex = 0;lineIndex < _drawOfLines;lineIndex++) {
CTLineRef line = CFArrayGetValueAtIndex(forecastLines,lineIndex);
CGPoint lineOrigin;

if (forecastMaxLineNumber >= _drawOfLines && _verticalTextAlignment != BDHKVerticalTextAlignmentTop) {
if (_verticalTextAlignment == BDHKVerticalTextAlignmentMiddle) {
float topMargin = lineOrigins[_drawOfLines - 1].y / 2.0;
lineOrigin = lineOrigins[lineIndex];
lineOrigin = CGPointMake(lineOrigin.x,lineOrigin.y - floorf(topMargin));
}
else if(_verticalTextAlignment == BDHKVerticalTextAlignmentBottom){
CGFloat ascent;
CGFloat descent;
CGFloat leading;
CTLineGetTypographicBounds(line, &ascent, &descent, &leading);
lineOrigin = lineOrigins[_drawOfLines - 1 - lineIndex];
lineOrigin = CGPointMake(lineOrigin.x, (self.height - floorf(lineOrigin.y + ascent - descent)));
}
}
else {
lineOrigin = lineOrigins[lineIndex];
}

CTLineRef lastLine = nil;
if (_drawOfLines < textMaxLineNumber) {
if (lineIndex == _drawOfLines - 1) {
CFRange range  = CTLineGetStringRange(line);
NSDictionary *attributes = [_attributedString attributesAtIndex:range.location + range.length - 1 effectiveRange:NULL];
NSAttributedString *token = [[NSAttributedString alloc] initWithString:@"\u2026" attributes:attributes];
if (_truncationEndAttributedString != nil) {
NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:token];
[attributedString appendAttributedString:_truncationEndAttributedString];
token = attributedString;
}
CFAttributedStringRef tokenRef = (__bridge CFAttributedStringRef)token;
CTLineRef truncationToken = CTLineCreateWithAttributedString(tokenRef);

NSRange lastLineRange = NSMakeRange(range.location, 0);
lastLineRange.length = [_attributedString length] - lastLineRange.location;
CFAttributedStringRef longString = (__bridge CFAttributedStringRef)[_attributedString attributedSubstringFromRange:lastLineRange];
CTLineRef endLine = CTLineCreateWithAttributedString(longString);
//lastLine = CTLineCreateTruncatedLine(endLine, self.width - _lastLineRightIndent, kCTLineTruncationEnd, truncationToken);
lastLine = CTLineCreateTruncatedLine(endLine, self.width, kCTLineTruncationEnd, truncationToken);

if (truncationToken) {
CFRelease(truncationToken);
}
if (endLine) {
CFRelease(endLine);
}
}
}
if (lastLine) {
CGContextSetTextPosition(context,lineOrigin.x,lineOrigin.y);
CTLineDraw(lastLine,context);

//从一行中得到CTRun数组,最后一个字的位置
//CFArrayRef runs = CTLineGetGlyphRuns(lastLine);
//long runCount = (long)CFArrayGetCount(runs);
//CTLineGetOffsetForStringIndex(line, runCount - 1, NULL);

CFRelease(lastLine);
}
else {
CGContextSetTextPosition(context,lineOrigin.x,lineOrigin.y);
CTLineDraw(line,context);
}
}

UIGraphicsPushContext(context);
CFRelease(textpath);
CFRelease(textFrame);
CFRelease(forecastFrame);
CFRelease(forecastPath);
CFRelease(framesetter);
}

#pragma mark --

- (NSMutableAttributedString *)attributedStringAddStyle:(NSString *)string
{
if (!string) {
return nil;
}

NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
style.lineSpacing = (_linesSpace > 0) ? _linesSpace : 4 ;
style.paragraphSpacing = 0;
style.alignment = self.textAlignment;

NSMutableAttributedString *attributedString =[[NSMutableAttributedString alloc]initWithString:string];
NSDictionary *attributes = @{NSForegroundColorAttributeName:self.textColor,NSFontAttributeName:self.font,NSParagraphStyleAttributeName:style};
[attributedString addAttributes:attributes range:NSMakeRange(0, [attributedString length])];

return attributedString;
}

#pragma mark --

- (void)setText:(NSString *)text
{
self.isDisplay = YES;
self.isText = YES;
[super setText:text];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
self.isDisplay = YES;
self.isText = NO;
[super setAttributedText:attributedText];
}

- (void)setTextColor:(UIColor *)textColor
{
self.isDisplay = YES;
[super setTextColor:textColor];
}

-(void)setTextAlignment:(NSTextAlignment)textAlignment
{
self.isDisplay = YES;
[super setTextAlignment:textAlignment];
}

-(void)setFont:(UIFont *)font
{
self.isDisplay = YES;
[super setFont:font];
}

-(void)setLinesSpace:(CGFloat)linesSpace
{
self.isDisplay = YES;
_linesSpace = linesSpace;
[self setNeedsDisplay];
}

-(void)setVerticalTextAlignment:(BDHKVerticalTextAlignment)verticalTextAlignment
{
_verticalTextAlignment = verticalTextAlignment;
[self setNeedsDisplay];
}

-(void)setMargin:(UIEdgeInsets)margin
{
_margin = margin;
[self setNeedsDisplay];
}

@end

@implementation NSString(BDHKLabelAttribute)

- (CGSize)sizeWithFont:(UIFont *)font width:(CGFloat)width linesSpace:(CGFloat)linesSpace numberOfLines:(NSInteger)numberOfLines
{
if (self.length <= 0) {
return CGSizeZero;
}

NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
style.lineSpacing = linesSpace ;
style.paragraphSpacing = 0;

NSMutableAttributedString *attributedString =[[NSMutableAttributedString alloc] initWithString:self];
NSDictionary *attributes = @{NSForegroundColorAttributeName:[UIColor blackColor],NSFontAttributeName:font,NSParagraphStyleAttributeName:style};
[attributedString addAttributes:attributes range:NSMakeRange(0, [attributedString length])];

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attributedString);
if (numberOfLines == 0) {
CGSize size = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, CFRangeMake(0, 0), NULL, CGSizeMake(width, 100000000), NULL);
size = CGSizeMake(ceilf(size.width), ceilf(size.height));
CFRelease(framesetter);
return size;
}

CGRect drawingRect = CGRectMake(0, 0, width, 100000000);
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, drawingRect);
CTFrameRef frameRef = CTFramesetterCreateFrame(framesetter,CFRangeMake(0,0), path, NULL);
CFArrayRef lines = CTFrameGetLines(frameRef);
long linesNumber = (long)CFArrayGetCount(lines);
if (linesNumber < 1) {//没有内容
CGPathRelease(path);
CFRelease(frameRef);
CFRelease(framesetter);
return CGSizeZero;
}

numberOfLines = (numberOfLines == 0) ? linesNumber : MIN(linesNumber, numberOfLines);

CGPoint lineOrigins[numberOfLines];
CTFrameGetLineOrigins(frameRef,CFRangeMake(0,numberOfLines), lineOrigins);

long lastLineNumber = MAX(numberOfLines - 1, 0);
CGPoint lineOrigin = lineOrigins[lastLineNumber];//最后一行line的位置
CTLineRef line = CFArrayGetValueAtIndex(lines, lastLineNumber);
CGFloat ascent;
CGFloat descent;
CGFloat leading;
CTLineGetTypographicBounds(line, &ascent, &descent, &leading);

/*
CGFloat height = drawingRect.size.height - floorf(lineOrigin.y) + ceilf(lineDescent);
if ([[UIDevice currentDevice].systemVersion floatValue] >= 10.0) {
height += ceilf(lineAscent / 2.0) + 2;
}
*/

CGFloat height = ceilf(drawingRect.size.height - lineOrigin.y + descent + leading);
if ([[UIDevice currentDevice].systemVersion floatValue] >= 10.0) {
height += ceilf(descent);
}

CGPathRelease(path);
CFRelease(frameRef);
CFRelease(framesetter);

return CGSizeMake(drawingRect.size.width, height);
}

@end