blocks|key|4472408|text|使用方法-+boundingRectWithSize:options:attributes:context:并将您的字体作为NSFontAttributeName键传递给NSAttributedString将为您提供所需的正确rect。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4472409|因此，您需要检查它是否大于标签边界减去偏移量。只有在是的时候，你才需要裁剪你的文本并在最后显示Read+More。|4472410|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/ios/documentation/UIKit/Reference/NSString_UIKit_Additions/#//apple_ref/occ/instm/NSString/boundingRectWithSize:options:attributes:context:^0|1Q|J|2D|I|4|1E|0|0|1B|9|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Using method <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/NSString_UIKit_Additions/#//apple_ref/occ/instm/NSString/boundingRectWithSize:options:attributes:context:" rel="nofollow">- boundingRectWithSize:options:attributes:context:</a> and passing your font as <code>NSFontAttributeName</code> key for <code>NSAttributedString</code> will give you the correct rect needed.

From that you need to check if it's bigger than your label bounds minus offset. Only if yes, you need to trim your text and show <code>Read More</code> at the end.

blocks|key|4471993|text|你知道吗，UILabel没有触摸动作。所以如果整个文本都在UILabel中，你就不能触摸'...Read+More‘。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4471994|注意:我的解决方案是，在UILabel的末尾添加一个清晰的背景按钮。|4471995|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Do you know there is no touch action of UILabel. so you cant touch '...Read More' if whole text in a UILabel.

Note: my solution is, add a clear background button end of the UILabel.

blocks|key|4472037|text|我的解决方案是，在UILabel的右下角和下方创建一个UIButton+(name+Read+more)。之后，我检查UILabel是否被截断以显示或隐藏UIButton|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4472038|CGSize+sizeOfText+=+[self.label.text+boundingRectWithSize:+CGSizeMake(self.label.intrinsicContentSize.width,+CGFLOAT_MAX)
+++++++++++++++++++++++++++++++++++++++++++++++++options:+(NSStringDrawingUsesLineFragmentOrigin%7CNSStringDrawingUsesFontLeading)
++++++++++++++++++++++++++++++++++++++++++++++attributes:+[NSDictionary+dictionaryWithObject:self.label.font+forKey:NSFontAttributeName]+context:+nil].size;
++++
if+(self.label.intrinsicContentSize.height+<+ceilf(sizeOfText.height))+{
++++//+label+is+truncated
++++self.readmoreButton.hidden+=+NO;+//+show+Read+more+button
}else{
++++self.readmoreButton.hidden+=+YES;
}|code-block|syntax|javascript|4472039|===+Swift+3版|4472040|let+textheight+=+self.label.text?.height(withConstrainedWidth:+self.label.frame.width,+font:+self.label.font)
++++if+self.label.intrinsicContentSize.height+<+textheight!+{
++++++++self.readmoreButton.isHidden+=+false
++++}else{
++++++++self.readmoreButton.isHidden+=+true
++++}|4472041|添加此扩展名：|4472042|extension+String+{

func+height(withConstrainedWidth+width:+CGFloat,+font:+UIFont)+->+CGFloat+{
++++let+constraintRect+=+CGSize(width:+width,+height:+.greatestFiniteMagnitude)
++++let+boundingBox+=+self.boundingRect(with:+constraintRect,+options:+.usesLineFragmentOrigin,+attributes:+[NSFontAttributeName:+font],+context:+nil)
++++
++++return+boundingBox.height
+}
}|4472043|希望这对你有所帮助|4472044|entityMap^0|9|7|R|8|1N|7|25|8|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|18|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1A|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|V|$]]

My solution is, I create a <code>UIButton</code> (name Read more) at bottom-right and below the <code>UILabel</code>.
After that I check the <code>UILabel</code> is truncated or not for showing or hiding the <code>UIButton</code>
<pre><code>CGSize sizeOfText = [self.label.text boundingRectWithSize: CGSizeMake(self.label.intrinsicContentSize.width, CGFLOAT_MAX)
 options: (NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading)
 attributes: [NSDictionary dictionaryWithObject:self.label.font forKey:NSFontAttributeName] context: nil].size;
 
if (self.label.intrinsicContentSize.height &lt; ceilf(sizeOfText.height)) {
 // label is truncated
 self.readmoreButton.hidden = NO; // show Read more button
}else{
 self.readmoreButton.hidden = YES;
}
</code></pre>
=== Swift 3 version
<pre><code>let textheight = self.label.text?.height(withConstrainedWidth: self.label.frame.width, font: self.label.font)
 if self.label.intrinsicContentSize.height &lt; textheight! {
 self.readmoreButton.isHidden = false
 }else{
 self.readmoreButton.isHidden = true
 }
</code></pre>
add this extension:
<pre><code>extension String {

func height(withConstrainedWidth width: CGFloat, font: UIFont) -&gt; CGFloat {
 let constraintRect = CGSize(width: width, height: .greatestFiniteMagnitude)
 let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)
 
 return boundingBox.height
 }
}
</code></pre>
Hope this help

blocks|key|4472546|text|你可以试试第三个库ExpandableLable|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4472547|将UILabel的自定义类设置为ExpandableLabel，并设置所需的行数和折叠文本：|4472548|expandableLabel.numberOfLines+=+5
expandableLabel.collapsedAttributedLink+=+NSAttributedString(string:+"more")
expandableLabel.ellipsis+=+NSAttributedString(string:+"...")
//+update+label+expand+or+collapse+state
expandableLabel.collapsed+=+true|code-block|syntax|javascript|4472549|您可能需要设置一个delegate，以便在链接被触摸时收到通知。|style|CODE|4472550|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/apploft/ExpandableLabel^0|9|F|0|0|0|0|9|8|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@$A|13|B|14|M|N]]|9|@]|C|$]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

You can try the 3rd library <a href="https://github.com/apploft/ExpandableLabel" rel="nofollow">ExpandableLable</a>

Set the custom class of your UILabel to ExpandableLabel and set the desired number of lines and collapsed text:

<pre><code>expandableLabel.numberOfLines = 5
expandableLabel.collapsedAttributedLink = NSAttributedString(string: "more")
expandableLabel.ellipsis = NSAttributedString(string: "...")
// update label expand or collapse state
expandableLabel.collapsed = true
</code></pre>

You may need set a <code>delegate</code> to get notified in case the link has been touched.

blocks|key|4472601|text|此方法适用于showless和带有向上向下箭头的showAll图像:在标签上添加点击手势|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4472602|++viewcontroller.h

++@property+(nonatomic,assign)+BOOL+isReadable;+

++viewcontrollr.m

++#pragma+mark+:-+Tap+Gesture+View+All
++-(void)readMoreDidClickedGesture+:(UITapGestureRecognizer+
++++*)objTapGesture{

+++++UILabel+*+lblDesc+=+(UILabel+*)[objTapGesture+view];
+++++NSLog(@"%25@",lblDesc.text);
+++++if+(self.isReadable+==+false)+{
+++++[self+setIsReadable:YES];
+++++lblDesc.text+=+readmoreText;
+++++readMoreHeight+=+[self+getLabelHeight:lblDesc];
+++++}
+++++else{
++++++readMoreHeight+=+30.0;
++++++[self+setIsReadable:NO];
++++++}++
++}



+-+(void)addReadMoreStringToUILabel:(UILabel*)label+isReaded:(BOOL)isReaded
+{

++NSString+*readMoreText+=+(isReaded+==+false)+?+@"...Show+All++"+:+
+++@"Show+Less++";
++NSInteger+lengthForString+=+label.text.length;
++if+(lengthForString+>=+30)
++{
++++NSInteger+lengthForVisibleString+=+[self+getLabelHeight:label];//[self+fitString:label.text+intoLabel:label];
++++NSMutableString+*mutableString+=+[[NSMutableString+alloc]+initWithString:label.text];
++++readmoreText+=+mutableString;
++++NSString+*trimmedString+=+[mutableString+stringByReplacingCharactersInRange:NSMakeRange(lengthForVisibleString,+(label.text.length+-+lengthForVisibleString))+withString:@""];
++++NSInteger+readMoreLength+=+readMoreText.length;
++++NSString+*trimmedForReadMore+=+[trimmedString+stringByReplacingCharactersInRange:NSMakeRange((trimmedString.length+-+readMoreLength),+readMoreLength)+withString:@""];
++++NSMutableAttributedString+*answerAttributed+=+[[NSMutableAttributedString+alloc]+initWithString:trimmedForReadMore+attributes:@{
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++NSFontAttributeName+:+label.font
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++}];


++++NSMutableAttributedString+*readMoreAttributed+=+[[NSMutableAttributedString+alloc]+initWithString:readMoreText+attributes:@{
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++NSFontAttributeName+:label.font,++++++++++++++++++++++++++++++NSForegroundColorAttributeName+:[UIColor+orangeColor]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++}];
++++if+(isReaded+==+false){
++++++++[readMoreAttributed+addAttribute:NSUnderlineStyleAttributeName
+++++++++++++++++++++++++++++value:@(NSUnderlineStyleSingle)
+++++++++++++++++++++++++++++range:NSMakeRange(3,+8)];

++++++++NSTextAttachment+*textAttachment+=+[[NSTextAttachment+alloc]+init];
++++++++UIImageView+*imgDown+=+[[UIImageView+alloc]initWithFrame:CGRectMake(0,+0,+25,+25)];
++++++++imgDown.image+=+[UIImage+imageNamed:@"searchFilterArrow1"];
++++++++imgDown.image+=+[imgDown.image+imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
++++++++[imgDown+setTintColor:[UIColor+orangeColor]];

++++++++textAttachment.image+=+imgDown.image;

++++++++NSAttributedString+*attrStringWithImage+=+[NSAttributedString+attributedStringWithAttachment:textAttachment];

++++++++[readMoreAttributed+replaceCharactersInRange:NSMakeRange(12,+1)+withAttributedString:attrStringWithImage];
++++}
++++else{
++++++++[readMoreAttributed+addAttribute:NSUnderlineStyleAttributeName
+++++++++++++++++++++++++++++++++++value:@(NSUnderlineStyleSingle)
+++++++++++++++++++++++++++++++++++range:NSMakeRange(1,+9)];
++++++++NSTextAttachment+*textAttachment+=+[[NSTextAttachment+alloc]+init];
++++++++UIImageView+*imgup+=+[[UIImageView+alloc]initWithFrame:CGRectMake(0,+0,+25,+25)];
++++++++imgup.image+=+[UIImage+imageNamed:@"searchFilterArrow2"];
++++++++imgup.image+=+[imgup.image+imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
++++++++[imgup+setTintColor:[UIColor+orangeColor]];

++++++++textAttachment.image+=+imgup.image;

++++++++NSAttributedString+*attrStringWithImage+=+[NSAttributedString+attributedStringWithAttachment:textAttachment];

++++++++[readMoreAttributed+replaceCharactersInRange:NSMakeRange(11,+1)+withAttributedString:attrStringWithImage];
++++}

++++[answerAttributed+appendAttributedString:readMoreAttributed];
++++label.attributedText+=+answerAttributed;

++++UITapGestureRecognizer+*readMoreGesture+=+[[UITapGestureRecognizer+alloc]+initWithTarget:self+action:@selector(readMoreDidClickedGesture:)];
++++readMoreGesture.numberOfTapsRequired+=+1;
++++[label+addGestureRecognizer:readMoreGesture];

++++label.userInteractionEnabled+=+YES;
}
else+{

++++NSLog(@"No+need+for+'Read+More'...");

}
}|code-block|syntax|javascript|4472603|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

this method is useful for showless and showAll with updown arrow image:
add tapgesture on label

<pre><code> viewcontroller.h

 @property (nonatomic,assign) BOOL isReadable; 

 viewcontrollr.m

 #pragma mark :- Tap Gesture View All
 -(void)readMoreDidClickedGesture :(UITapGestureRecognizer 
 *)objTapGesture{

 UILabel * lblDesc = (UILabel *)[objTapGesture view];
 NSLog(@"%@",lblDesc.text);
 if (self.isReadable == false) {
 [self setIsReadable:YES];
 lblDesc.text = readmoreText;
 readMoreHeight = [self getLabelHeight:lblDesc];
 }
 else{
 readMoreHeight = 30.0;
 [self setIsReadable:NO];
 } 
 }



 - (void)addReadMoreStringToUILabel:(UILabel*)label isReaded:(BOOL)isReaded
 {

 NSString *readMoreText = (isReaded == false) ? @"...Show All " : 
 @"Show Less ";
 NSInteger lengthForString = label.text.length;
 if (lengthForString &gt;= 30)
 {
 NSInteger lengthForVisibleString = [self getLabelHeight:label];//[self fitString:label.text intoLabel:label];
 NSMutableString *mutableString = [[NSMutableString alloc] initWithString:label.text];
 readmoreText = mutableString;
 NSString *trimmedString = [mutableString stringByReplacingCharactersInRange:NSMakeRange(lengthForVisibleString, (label.text.length - lengthForVisibleString)) withString:@""];
 NSInteger readMoreLength = readMoreText.length;
 NSString *trimmedForReadMore = [trimmedString stringByReplacingCharactersInRange:NSMakeRange((trimmedString.length - readMoreLength), readMoreLength) withString:@""];
 NSMutableAttributedString *answerAttributed = [[NSMutableAttributedString alloc] initWithString:trimmedForReadMore attributes:@{
 NSFontAttributeName : label.font
 }];


 NSMutableAttributedString *readMoreAttributed = [[NSMutableAttributedString alloc] initWithString:readMoreText attributes:@{
 NSFontAttributeName :label.font, NSForegroundColorAttributeName :[UIColor orangeColor]
 }];
 if (isReaded == false){
 [readMoreAttributed addAttribute:NSUnderlineStyleAttributeName
 value:@(NSUnderlineStyleSingle)
 range:NSMakeRange(3, 8)];

 NSTextAttachment *textAttachment = [[NSTextAttachment alloc] init];
 UIImageView *imgDown = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 25, 25)];
 imgDown.image = [UIImage imageNamed:@"searchFilterArrow1"];
 imgDown.image = [imgDown.image imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
 [imgDown setTintColor:[UIColor orangeColor]];

 textAttachment.image = imgDown.image;

 NSAttributedString *attrStringWithImage = [NSAttributedString attributedStringWithAttachment:textAttachment];

 [readMoreAttributed replaceCharactersInRange:NSMakeRange(12, 1) withAttributedString:attrStringWithImage];
 }
 else{
 [readMoreAttributed addAttribute:NSUnderlineStyleAttributeName
 value:@(NSUnderlineStyleSingle)
 range:NSMakeRange(1, 9)];
 NSTextAttachment *textAttachment = [[NSTextAttachment alloc] init];
 UIImageView *imgup = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 25, 25)];
 imgup.image = [UIImage imageNamed:@"searchFilterArrow2"];
 imgup.image = [imgup.image imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
 [imgup setTintColor:[UIColor orangeColor]];

 textAttachment.image = imgup.image;

 NSAttributedString *attrStringWithImage = [NSAttributedString attributedStringWithAttachment:textAttachment];

 [readMoreAttributed replaceCharactersInRange:NSMakeRange(11, 1) withAttributedString:attrStringWithImage];
 }

 [answerAttributed appendAttributedString:readMoreAttributed];
 label.attributedText = answerAttributed;

 UITapGestureRecognizer *readMoreGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(readMoreDidClickedGesture:)];
 readMoreGesture.numberOfTapsRequired = 1;
 [label addGestureRecognizer:readMoreGesture];

 label.userInteractionEnabled = YES;
}
else {

 NSLog(@"No need for 'Read More'...");

}
}
</code></pre>

blocks|key|4472176|text|这适用于Swift+5|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4472177|这里是@ramchandran答案的一个更安全的版本，因为您不知道用户将输入多少个字符。|4472178|在他的回答中，如果用户输入的字符串长度小于您决定用于...+Readmore的任何文本的长度，那么它将崩溃。例如，这就是你使用它的方式|offset|length|style|CODE|4472179|if+yourLabel.text!.count+>+1+{

+++let+readmoreFont+=+UIFont(name:+"Helvetica-Oblique",+size:+11.0)
++++let+readmoreFontColor+=+UIColor.blue
++++DispatchQueue.main.async+{
++++++++self.yourLabel.addTrailing(with:+"...+",+moreText:+"Readmore",+moreTextFont:+readmoreFont!,+moreTextColor:+readmoreFontColor)
++++}
}|code-block|syntax|javascript|4472180|在上面的例子中，...+Readmore的输出总共是12个字符。如果用户输入的字符串是yourLabel.text+=+"12345678"，那么字符串的文本将只有8个字符。它会崩溃，因为在下面一行中使用((trimmedString?.count+??+0)+-+readMoreLength)的范围将产生负结果：|4472181|//+“12345678”+minus+“...+Readmore”+=+negative+four+(8+-+12+=+-4)
let+trimmedForReadMore:+String+=+(trimmedString!+as+NSString).replacingCharacters(in:+NSRange(location:+((trimmedString?.count+??+0)+-+readMoreLength),+length:+readMoreLength),+with:+"")+%2B+trailingText|4472182|我添加了一个安全检查，以确保如果输入的字符串少于或等于您决定用作...+Readmore的任何字符串的字符数，它将返回，并且将导致崩溃的行永远不会到达：|4472183|//+trimmedString+is+the+string+the+user+entered
guard+let+safeTrimmedString+=+trimmedString+else+{+return+}
if+safeTrimmedString.count+<=+readMoreLength+{+return+}|4472184|它位于addTrailing函数的中心|4472185|extension+UILabel{++++
++++
++++func+addTrailing(with+trailingText:+String,+moreText:+String,+moreTextFont:+UIFont,+moreTextColor:+UIColor)+{
++++++++
++++++++let+readMoreText:+String+=+trailingText+%2B+moreText
++++++++
++++++++if+self.visibleTextLength+==+0+{+return+}
++++++++
++++++++let+lengthForVisibleString:+Int+=+self.visibleTextLength
++++++++
++++++++if+let+myText+=+self.text+{
++++++++++++
++++++++++++let+mutableString:+String+=+myText
++++++++++++
++++++++++++let+trimmedString:+String?+=+(mutableString+as+NSString).replacingCharacters(in:+NSRange(location:+lengthForVisibleString,+length:+myText.count+-+lengthForVisibleString),+with:+"")
++++++++++++
++++++++++++let+readMoreLength:+Int+=+(readMoreText.count)
++++++++++++
++++++++++++guard+let+safeTrimmedString+=+trimmedString+else+{+return+}
++++++++++++
++++++++++++if+safeTrimmedString.count+<=+readMoreLength+{+return+}
++++++++++++
++++++++++++print("this+number+\(safeTrimmedString.count)+should+never+be+less\n")
++++++++++++print("then+this+number+\(readMoreLength)")
++++++++++++
++++++++++++//+"safeTrimmedString.count+-+readMoreLength"+should+never+be+less+then+the+readMoreLength+because+it'll+be+a+negative+value+and+will+crash
++++++++++++let+trimmedForReadMore:+String+=+(safeTrimmedString+as+NSString).replacingCharacters(in:+NSRange(location:+safeTrimmedString.count+-+readMoreLength,+length:+readMoreLength),+with:+"")+%2B+trailingText
++++++++++++
++++++++++++let+answerAttributed+=+NSMutableAttributedString(string:+trimmedForReadMore,+attributes:+[NSAttributedString.Key.font:+self.font])
++++++++++++let+readMoreAttributed+=+NSMutableAttributedString(string:+moreText,+attributes:+[NSAttributedString.Key.font:+moreTextFont,+NSAttributedString.Key.foregroundColor:+moreTextColor])
++++++++++++answerAttributed.append(readMoreAttributed)
++++++++++++self.attributedText+=+answerAttributed
++++++++}
++++}
++++
++++var+visibleTextLength:+Int+{
++++++++
++++++++let+font:+UIFont+=+self.font
++++++++let+mode:+NSLineBreakMode+=+self.lineBreakMode
++++++++let+labelWidth:+CGFloat+=+self.frame.size.width
++++++++let+labelHeight:+CGFloat+=+self.frame.size.height
++++++++let+sizeConstraint+=+CGSize(width:+labelWidth,+height:+CGFloat.greatestFiniteMagnitude)
++++++++
++++++++if+let+myText+=+self.text+{
++++++++++++
++++++++++++let+attributes:+[AnyHashable:+Any]+=+[NSAttributedString.Key.font:+font]
++++++++++++let+attributedText+=+NSAttributedString(string:+myText,+attributes:+attributes+as?+[NSAttributedString.Key+:+Any])
++++++++++++let+boundingRect:+CGRect+=+attributedText.boundingRect(with:+sizeConstraint,+options:+.usesLineFragmentOrigin,+context:+nil)
++++++++++++
++++++++++++if+boundingRect.size.height+>+labelHeight+{
++++++++++++++++var+index:+Int+=+0
++++++++++++++++var+prev:+Int+=+0
++++++++++++++++let+characterSet+=+CharacterSet.whitespacesAndNewlines
++++++++++++++++repeat+{
++++++++++++++++++++prev+=+index
++++++++++++++++++++if+mode+==+NSLineBreakMode.byCharWrapping+{
++++++++++++++++++++++++index+%2B=+1
++++++++++++++++++++}+else+{
++++++++++++++++++++++++index+=+(myText+as+NSString).rangeOfCharacter(from:+characterSet,+options:+[],+range:+NSRange(location:+index+%2B+1,+length:+myText.count+-+index+-+1)).location
++++++++++++++++++++}
++++++++++++++++}+while+index+!=+NSNotFound+&&+index+<+myText.count+&&+(myText+as+NSString).substring(to:+index).boundingRect(with:+sizeConstraint,+options:+.usesLineFragmentOrigin,+attributes:+attributes+as?+[NSAttributedString.Key+:+Any],+context:+nil).size.height+<=+labelHeight
++++++++++++++++return+prev
++++++++++++}
++++++++}
++++++++
++++++++if+self.text+==+nil+{
++++++++++++return+0
++++++++}+else+{
++++++++++++return+self.text!.count
++++++++}
++++}
}|4472186|entityMap^0|0|0|Q|C|0|0|8|C|17|R|2U|1A|0|0|W|C|0|0|3|B|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|14|8|@$F|15|G|16|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|17|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|18|8|@$F|19|G|1A|H|I]|$F|1B|G|1C|H|I]|$F|1D|G|1E|H|I]]|9|@]|A|$]]|$1|Q|3|R|5|L|7|1F|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1G|8|@$F|1H|G|1I|H|I]]|9|@]|A|$]]|$1|U|3|V|5|L|7|1J|8|@]|9|@]|A|$M|N]]|$1|W|3|X|5|6|7|1K|8|@$F|1L|G|1M|H|I]]|9|@]|A|$]]|$1|Y|3|Z|5|L|7|1N|8|@]|9|@]|A|$M|N]]|$1|10|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|11|$]]

This works for Swift 5
Here is a safer version of @ramchandran's answer because you don’t know how many characters the user will enter.
In his answer if the length of the string the user entered is less then the length of the whatever text you decide to use for <code>... Readmore</code> then it will crash. For eg this is how you use it
<pre><code>if yourLabel.text!.count &gt; 1 {

 let readmoreFont = UIFont(name: &quot;Helvetica-Oblique&quot;, size: 11.0)
 let readmoreFontColor = UIColor.blue
 DispatchQueue.main.async {
 self.yourLabel.addTrailing(with: &quot;... &quot;, moreText: &quot;Readmore&quot;, moreTextFont: readmoreFont!, moreTextColor: readmoreFontColor)
 }
}
</code></pre>
In the above example the output of <code>... Readmore</code> is 12 characters total. If the string the user entered was <code>yourLabel.text = &quot;12345678&quot;</code> then the string's text would only be 8 characters.
It would crash because the range using <code>((trimmedString?.count ?? 0) - readMoreLength)</code> in the line below would produce a negative result:
<pre><code>// “12345678” minus “... Readmore” = negative four (8 - 12 = -4)
let trimmedForReadMore: String = (trimmedString! as NSString).replacingCharacters(in: NSRange(location: ((trimmedString?.count ?? 0) - readMoreLength), length: readMoreLength), with: &quot;&quot;) + trailingText
</code></pre>
I added a safety check to make sure that if the string entered is less then or equal to the number of characters for whatever you decide to use as <code>... Readmore</code> it will return and the line that will cause the crash will never get reached:
<pre><code>// trimmedString is the string the user entered
guard let safeTrimmedString = trimmedString else { return }
if safeTrimmedString.count &lt;= readMoreLength { return }
</code></pre>
It's located in the center of the <code>addTrailing</code> function
<pre><code>extension UILabel{ 
 
 func addTrailing(with trailingText: String, moreText: String, moreTextFont: UIFont, moreTextColor: UIColor) {
 
 let readMoreText: String = trailingText + moreText
 
 if self.visibleTextLength == 0 { return }
 
 let lengthForVisibleString: Int = self.visibleTextLength
 
 if let myText = self.text {
 
 let mutableString: String = myText
 
 let trimmedString: String? = (mutableString as NSString).replacingCharacters(in: NSRange(location: lengthForVisibleString, length: myText.count - lengthForVisibleString), with: &quot;&quot;)
 
 let readMoreLength: Int = (readMoreText.count)
 
 guard let safeTrimmedString = trimmedString else { return }
 
 if safeTrimmedString.count &lt;= readMoreLength { return }
 
 print(&quot;this number \(safeTrimmedString.count) should never be less\n&quot;)
 print(&quot;then this number \(readMoreLength)&quot;)
 
 // &quot;safeTrimmedString.count - readMoreLength&quot; should never be less then the readMoreLength because it'll be a negative value and will crash
 let trimmedForReadMore: String = (safeTrimmedString as NSString).replacingCharacters(in: NSRange(location: safeTrimmedString.count - readMoreLength, length: readMoreLength), with: &quot;&quot;) + trailingText
 
 let answerAttributed = NSMutableAttributedString(string: trimmedForReadMore, attributes: [NSAttributedString.Key.font: self.font])
 let readMoreAttributed = NSMutableAttributedString(string: moreText, attributes: [NSAttributedString.Key.font: moreTextFont, NSAttributedString.Key.foregroundColor: moreTextColor])
 answerAttributed.append(readMoreAttributed)
 self.attributedText = answerAttributed
 }
 }
 
 var visibleTextLength: Int {
 
 let font: UIFont = self.font
 let mode: NSLineBreakMode = self.lineBreakMode
 let labelWidth: CGFloat = self.frame.size.width
 let labelHeight: CGFloat = self.frame.size.height
 let sizeConstraint = CGSize(width: labelWidth, height: CGFloat.greatestFiniteMagnitude)
 
 if let myText = self.text {
 
 let attributes: [AnyHashable: Any] = [NSAttributedString.Key.font: font]
 let attributedText = NSAttributedString(string: myText, attributes: attributes as? [NSAttributedString.Key : Any])
 let boundingRect: CGRect = attributedText.boundingRect(with: sizeConstraint, options: .usesLineFragmentOrigin, context: nil)
 
 if boundingRect.size.height &gt; labelHeight {
 var index: Int = 0
 var prev: Int = 0
 let characterSet = CharacterSet.whitespacesAndNewlines
 repeat {
 prev = index
 if mode == NSLineBreakMode.byCharWrapping {
 index += 1
 } else {
 index = (myText as NSString).rangeOfCharacter(from: characterSet, options: [], range: NSRange(location: index + 1, length: myText.count - index - 1)).location
 }
 } while index != NSNotFound &amp;&amp; index &lt; myText.count &amp;&amp; (myText as NSString).substring(to: index).boundingRect(with: sizeConstraint, options: .usesLineFragmentOrigin, attributes: attributes as? [NSAttributedString.Key : Any], context: nil).size.height &lt;= labelHeight
 return prev
 }
 }
 
 if self.text == nil {
 return 0
 } else {
 return self.text!.count
 }
 }
}
</code></pre>

blocks|key|4472782|text|对于标签上的操作，如果使用CollectionView或TableView，则可以使用委托方法来执行操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4472783|func+showMore(cell:+CustomCell)+{
++++guard+let+indexPath+=+self.tableView.indexPath(for:+cell)+else+{
++++++++return
++++}
++++let+cell+=+tableView.cellForRow(at:+indexPath)+as!+CustomCell
++++tableView.beginUpdates()
++++cell.label.text+=+"your+complete+text"
++++tableView.endUpdates()
}|code-block|syntax|javascript|4472784|这将更新标签，并根据需要使用Lance+Samaria+answer显示全文，并为单元格添加操作。|4472785|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For Action on the label, if using a CollectionView or TableView you could use a delegate method to perform the action.

<pre><code>func showMore(cell: CustomCell) {
 guard let indexPath = self.tableView.indexPath(for: cell) else {
 return
 }
 let cell = tableView.cellForRow(at: indexPath) as! CustomCell
 tableView.beginUpdates()
 cell.label.text = "your complete text"
 tableView.endUpdates()
}
</code></pre>

This updates the label and displays the full text as required
Using Lance Samaria answer and adding the action for the cell.

blocks|key|4472908|text|class+DynamicLabel:+UILabel{

++++var+fullText:+String?
++++var+truncatedLength+=+100
++++var+isTruncated+=+true

++++func+collapse(){
++++++++let+index+=+fullText!.index(fullText!.startIndex,+offsetBy:+truncatedLength)
++++++++self.text+=+fullText![...index].description+%2B+"...+More"
++++++++isTruncated+=+true
++++}

++++func+expand(){
++++++++self.text+=+fullText
++++++++isTruncated+=+false
++++}

}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4472909|这只是一个简单的技巧来完成所有这些杂乱的实现。想法很简单，我们不设置折叠或展开行，只需将标签设置为0。然后将原始文本存储在fullText变量中。现在，如果我们想要显示折叠格式，那么只需获取substring并添加自定义省略号即可。|unstyled|offset|length|style|CODE|4472910|注意:这不包括点击事件处理程序，你可以自己在控制器上添加它。|4472911|entityMap^0|0|1P|8|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@$G|Q|H|R|I|J]]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|F|7|T|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>class DynamicLabel: UILabel{

 var fullText: String?
 var truncatedLength = 100
 var isTruncated = true

 func collapse(){
 let index = fullText!.index(fullText!.startIndex, offsetBy: truncatedLength)
 self.text = fullText![...index].description + "... More"
 isTruncated = true
 }

 func expand(){
 self.text = fullText
 isTruncated = false
 }

}
</code></pre>

Just a simple trick to get through all these messy implementations. The idea is simple, we don't set collapsed or expand rows, just set the label to 0.
Then store the original text on <code>fullText</code> variable. Now if we want to display collapsed format, then just get substring and add the custom ellipsis.

Note: This does not include tap event handlers, you can add it yourself on the controller.

blocks|key|4472496|text|我不能让任何东西在这里工作，所以我发布了我的解决方案。我有一个UILabel，应该是3行，在文本的末尾应该是...阅读更多。我做了一个UIFont扩展，它计算具有特定字体和宽度的字符串的高度，然后我做了一个字符串扩展，它递归地使字符串变小，直到它适合x行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4472497|extension+String+{
++++/**
This+method+returns+a+substring+of+a+string+that+fits+in+a+label+with+a+specific+width+and+number+of+lines
It+has+optional+suffix+so+you+can+add+your+own+ellipsis,+like+"...+Read+more"
+-+Parameter+width:+The+label+width+that+constrains+the+text.+Make+sure+to+call+it+after+subViews+have+been+laid+out
+-+Parameter+lines:+Number+of+allowed+lines+in+the+label
+-+Parameter+font:+The+font+to+use+with+the+label
+-+Parameter+suffix:+Custom+string+that+will+be+added+to+the+string+and+will+fit+within+the+width/lines+constraint
+-+Returns:+A+substring+that+fits+within+the+constraints+given
+*/
func+textThatFits(width:+CGFloat,+lines:+Int,+font:+UIFont,+suffix:+String+=+"")+->+String+{
++++let+lineHeight+=+font.lineHeight
++++let+completeString+=+self+%2B+suffix
++++let+size+=+font.sizeOfString(completeString,+constrainedToWidth:+width)
++++if+size.height+>+lineHeight+*+CGFloat(lines)+{
++++++++let+partialString+=+self.components(separatedBy:+"+").dropLast().joined(separator:+"+")
++++++++return+partialString.textThatFits(width:+width,+lines:+lines,+font:+font,+suffix:+suffix)
++++}+else+{
++++++++return+completeString
++++}
}
}

extension+UIFont+{
++++/**
+Calculate+the+height+of+a+string+with+this+font+and+constrained+width
+-+Parameter+string:+String+to+calculate+size+for
+-+Parameter+width:+The+constrained+width+for+the+bounding+box+when+calculating+the+size
+-+Returns:+Size+of+string+contained+in+bounding+rect+of+width+and+max+height
+*/
func+sizeOfString(_+string:+String,+constrainedToWidth+width:+Double)+->+CGSize+{
++++return+(string+as+NSString).boundingRect(
++++++++with:+CGSize(width:+width,+height:+.greatestFiniteMagnitude),
++++++++options:+[.usesFontLeading,+.usesLineFragmentOrigin],
++++++++attributes:+[.font:+self],
++++++++context:+nil).size
}
}|code-block|syntax|javascript|4472498|然后我不得不从viewDidLayoutSubviews调用它，因为在此之前我的标签的宽度并不正确。最后，我是这样使用的：|4472499|private+func+setReadMoreText()+{
++++let+readMoreSuffix+=+"...+Read+more"
++++let+font+=+//+YOUR_FONT
++++let+fittingString+=+YOUR_LONG_STRING.textThatFits(width:+YOUR_UILABEL.frame.width,+lines:+NUMBER_OF_LINES,+font:+font,+suffix:+readMoreSuffix)
++++//+This+is+not+needed+but+I+wanted+the+Read+more+text+to+be+colored.+You+could+just+set+your+fittingString+directly+as+text.
++++let+privacyAttrString+=+NSMutableAttributedString(string:+fittingString,+attributes:+[.font:+font])
++++privacyAttrString.addAttributes([.foregroundColor:+YOUR_COLOR],+range:+NSRange(location:+fittingString.count+-+readMoreSuffix.count+%2B+4,+length:+readMoreSuffix.count+-+4))
++++self.YOUR_UILABEL.text+=+privacyAttrString
}|4472500|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I couldn't get anything here to work so I'm posting my solution. I had a UILabel that was supposed to be 3 lines and at the end of the text it should read ... Read more. I made a UIFont extension that calculates the height of a string with a particular font and width and then I made a String extension that recursively makes a string smaller until it fits into x lines.
<pre><code>extension String {
 /**
This method returns a substring of a string that fits in a label with a specific width and number of lines
It has optional suffix so you can add your own ellipsis, like &quot;... Read more&quot;
 - Parameter width: The label width that constrains the text. Make sure to call it after subViews have been laid out
 - Parameter lines: Number of allowed lines in the label
 - Parameter font: The font to use with the label
 - Parameter suffix: Custom string that will be added to the string and will fit within the width/lines constraint
 - Returns: A substring that fits within the constraints given
 */
func textThatFits(width: CGFloat, lines: Int, font: UIFont, suffix: String = &quot;&quot;) -&gt; String {
 let lineHeight = font.lineHeight
 let completeString = self + suffix
 let size = font.sizeOfString(completeString, constrainedToWidth: width)
 if size.height &gt; lineHeight * CGFloat(lines) {
 let partialString = self.components(separatedBy: &quot; &quot;).dropLast().joined(separator: &quot; &quot;)
 return partialString.textThatFits(width: width, lines: lines, font: font, suffix: suffix)
 } else {
 return completeString
 }
}
}

extension UIFont {
 /**
 Calculate the height of a string with this font and constrained width
 - Parameter string: String to calculate size for
 - Parameter width: The constrained width for the bounding box when calculating the size
 - Returns: Size of string contained in bounding rect of width and max height
 */
func sizeOfString(_ string: String, constrainedToWidth width: Double) -&gt; CGSize {
 return (string as NSString).boundingRect(
 with: CGSize(width: width, height: .greatestFiniteMagnitude),
 options: [.usesFontLeading, .usesLineFragmentOrigin],
 attributes: [.font: self],
 context: nil).size
}
}
</code></pre>
Then I had to call it from viewDidLayoutSubviews since my label's width wasn't correct until then. Lastly, I used this like this:
<pre><code>private func setReadMoreText() {
 let readMoreSuffix = &quot;... Read more&quot;
 let font = // YOUR_FONT
 let fittingString = YOUR_LONG_STRING.textThatFits(width: YOUR_UILABEL.frame.width, lines: NUMBER_OF_LINES, font: font, suffix: readMoreSuffix)
 // This is not needed but I wanted the Read more text to be colored. You could just set your fittingString directly as text.
 let privacyAttrString = NSMutableAttributedString(string: fittingString, attributes: [.font: font])
 privacyAttrString.addAttributes([.foregroundColor: YOUR_COLOR], range: NSRange(location: fittingString.count - readMoreSuffix.count + 4, length: readMoreSuffix.count - 4))
 self.YOUR_UILABEL.text = privacyAttrString
}
</code></pre>

I have a <code>UILabel</code> and in some cases the text is longer then the <code>UILabel</code> itself, so I see the text as <code>"bla bla bla..."</code> I want to add a <code>...Read More</code> button text at the end of the <code>UILabel</code>..

I've read some posts but they offer solutions that are not good to me, for example: to calculate how many characters will enter the <code>UILabel</code>, but with the font i'm using each character has a different width.

How can I manage to do that?

Thanks in advance!

Add "...Read More" to the end of UILabel

我有一个UILabel，在某些情况下，文本比UILabel本身还要长，所以我将文本看作"bla bla bla..."，我想在UILabel的末尾添加一个...Read More按钮文本。我读过一些帖子，但他们提供的解决方案对我来说并不好，例如:计算有多少个字符将进入UILabel，但我使用的字体每个字符都有不同的宽度...

问在UILabel末尾添加"...Read More“
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