CGSize maximumLabelSize = CGSizeMake(label.frame.size.width, FLT_MAX);
CGSize expectedLabelSize = [label sizeThatFits:maximumLabelSize];
float heightUse = expectedLabelSize.height;

创建一个接受UILabel实例的函数。并返回CGSize

CGSize constraint = CGSizeMake(label.frame.size.width , 2000.0);
// Adjust according to requirement

CGSize size;
if([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0){

    NSRange range = NSMakeRange(0, [label.attributedText length]);

    NSDictionary *attributes = [label.attributedText attributesAtIndex:0 effectiveRange:&range];
    CGSize boundingBox = [label.text boundingRectWithSize:constraint options: NSStringDrawingUsesLineFragmentOrigin attributes:attributes context:nil].size;

    size = CGSizeMake(ceil(boundingBox.width), ceil(boundingBox.height));
}
else{
    size = [label.text sizeWithFont:label.font constrainedToSize:constraint lineBreakMode:label.lineBreakMode];
}

return size;

boundingRectWithSize:options:attributes:context:

试试这个语法:

NSAttributedString *attributedText =
    [[NSAttributedString alloc] initWithString:text 
                                    attributes:@{NSFontAttributeName: font}];

CGSize maximumLabelSize = CGSizeMake(label.frame.size.width, FLT_MAX);
CGSize expectedLabelSize = [label sizeThatFits:maximumLabelSize];
float heightUse = expectedLabelSize.height;

你仍然可以使用sizeWithFont。但是，在iOS >= 7.0中，如果字符串包含开头和结尾空格或结束行\n，则会导致崩溃。

在使用文本之前修剪文本

label.text = [label.text stringByTrimmingCharactersInSet:
             [NSCharacterSet whitespaceAndNewlineCharacterSet]];

这也适用于sizeWithAttributes和[label sizeToFit]。

此外，当你有nsstringdrawingtextstorage消息发送到deallocated实例在ios7.0设备它处理这个。