就像这样做

NSString * strCheck = @"A\nB";

strCheck = [strCheck stringByReplacingOccurrencesOfString:@"\\n" withString:@"\n"];  //This is to prevent for fetching string from plist or data structure

label.numberOfLines = 0;

label.lineBreakMode = NSLineBreakByWordWrapping;

label.text = strCheck;

textLabel.text = @"\nAAAAA\nBBBBB\nCCCCC";
textLabel.numberOfLines = 3; \\As you want - AAAAA\nBBBBB\nCCCCC
textLabel.lineBreakMode = UILineBreakModeWordWrap;
NSLog(@"The textLabel text is - %@",textLabel.text);

在Xcode 6中，当使用换行时，你甚至可以在字符串中使用\n。它会起作用的。例如:

UILabel *label = [[UILabel alloc]initWithFrame:CGRectMake(0, 100, screenRect.size.width, 50)];
label.textAlignment = NSTextAlignmentCenter;
label.text = @"This will be on the first line\nfollowed by a line under it.";
label.lineBreakMode = UILineBreakModeWordWrap;
label.numberOfLines = 0;

对我来说，改变标签帧大小似乎是错误的，尤其是在使用自动布局时。使用appendFormat方法似乎更合适。以下是我的例子:

NSMutableString *list = [[NSMutableString alloc] init];
NSArray *textArray = @[@"AAAA", @"BBBB"];
for (NSString *string in textArray) {
    [list appendFormat:@"%@\n", string.mutableCopy];
}
self.label.text = list;
self.label.numberOfLines = 0;

只是使用标签。numberolines = 0;

重要的是要注意它是\n(反斜杠)而不是/n。