While the UITextField class has no max length property, it's relatively simple to get this functionality by setting the text field's delegate and implementing the following delegate method:

Objective-C

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    // Prevent crashing undo bug – see note below.
    if(range.length + range.location > textField.text.length)
    {
        return NO;
    }
        
    NSUInteger newLength = [textField.text length] + [string length] - range.length;
    return newLength <= 25;
}

Swift

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    
    let currentCharacterCount = textField.text?.count ?? 0
    if range.length + range.location > currentCharacterCount {
        return false
    }
    let newLength = currentCharacterCount + string.count - range.length
    return newLength <= 25
}

Before the text field changes, the UITextField asks the delegate if the specified text should be changed. The text field has not changed at this point, so we grab it's current length and the string length we're inserting (either through pasting copied text or typing a single character using the keyboard), minus the range length. If this value is too long (more than 25 characters in this example), return NO to prohibit the change.

When typing in a single character at the end of a text field, the range.location will be the current field's length, and range.length will be 0 because we're not replacing/deleting anything. Inserting into the middle of a text field just means a different range.location, and pasting multiple characters just means string has more than one character in it.

Deleting single characters or cutting multiple characters is specified by a range with a non-zero length, and an empty string. Replacement is just a range deletion with a non-empty string.

A note on the crashing "undo" bug

As is mentioned in the comments, there is a bug with UITextField that can lead to a crash.

If you paste in to the field, but the paste is prevented by your validation implementation, the paste operation is still recorded in the application's undo buffer. If you then fire an undo (by shaking the device and confirming an Undo), the UITextField will attempt to replace the string it thinks it pasted in to itself with an empty string. This will crash because it never actually pasted the string in to itself. It will try to replace a part of the string that doesn't exist.

Fortunately you can protect the UITextField from killing itself like this. You just need to ensure that the range it proposes to replace does exist within its current string. This is what the initial sanity check above does.

swift 3.0 with copy and paste working fine.

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        let str = (textView.text + text)
        if str.characters.count <= 10 {
            return true
        }
        textView.text = str.substring(to: str.index(str.startIndex, offsetBy: 10))
        return false
    }

Hope it's helpful to you.

There's no way to set the vertical-align on a UILabel, but you can get the same effect by changing the label's frame. I've made my labels orange so you can see clearly what's happening.

Here's the quick and easy way to do this:

    [myLabel sizeToFit];

If you have a label with longer text that will make more than one line, set numberOfLines to 0 (zero here means an unlimited number of lines).

    myLabel.numberOfLines = 0;
    [myLabel sizeToFit];

Longer Version

I'll make my label in code so that you can see what's going on. You can set up most of this in Interface Builder too. My setup is a View-Based App with a background image I made in Photoshop to show margins (20 points). The label is an attractive orange color so you can see what's going on with the dimensions.

- (void)viewDidLoad
{
    [super viewDidLoad];

    // 20 point top and left margin. Sized to leave 20 pt at right.
    CGRect labelFrame = CGRectMake(20, 20, 280, 150);
    UILabel *myLabel = [[UILabel alloc] initWithFrame:labelFrame];
    [myLabel setBackgroundColor:[UIColor orangeColor]];

    NSString *labelText = @"I am the very model of a modern Major-General, I've information vegetable, animal, and mineral";
    [myLabel setText:labelText];

    // Tell the label to use an unlimited number of lines
    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

    [self.view addSubview:myLabel];
}

Some limitations of using sizeToFit come into play with center- or right-aligned text. Here's what happens:

    // myLabel.textAlignment = NSTextAlignmentRight;
    myLabel.textAlignment = NSTextAlignmentCenter;

    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

The label is still sized with a fixed top-left corner. You can save the original label's width in a variable and set it after sizeToFit, or give it a fixed width to counter these problems:

    myLabel.textAlignment = NSTextAlignmentCenter;

    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

    CGRect myFrame = myLabel.frame;
    // Resize the frame's width to 280 (320 - margins)
    // width could also be myOriginalLabelFrame.size.width
    myFrame = CGRectMake(myFrame.origin.x, myFrame.origin.y, 280, myFrame.size.height);
    myLabel.frame = myFrame;

Note that sizeToFit will respect your initial label's minimum width. If you start with a label 100 wide and call sizeToFit on it, it will give you back a (possibly very tall) label with 100 (or a little less) width. You might want to set your label to the minimum width you want before resizing.

Some other things to note:

Whether lineBreakMode is respected depends on how it's set. NSLineBreakByTruncatingTail (the default) is ignored after sizeToFit, as are the other two truncation modes (head and middle). NSLineBreakByClipping is also ignored. NSLineBreakByCharWrapping works as usual. The frame width is still narrowed to fit to the rightmost letter.

Mark Amery gave a fix for NIBs and Storyboards using Auto Layout in the comments:

If your label is included in a nib or storyboard as a subview of the view of a ViewController that uses autolayout, then putting your sizeToFit call into viewDidLoad won't work, because autolayout sizes and positions the subviews after viewDidLoad is called and will immediately undo the effects of your sizeToFit call. However, calling sizeToFit from within viewDidLayoutSubviews will work.

This uses the NSString method sizeWithFont:constrainedToSize:lineBreakMode: to calculate the frame height needed to fit a string, then sets the origin and width.

Resize the frame for the label using the text you want to insert. That way you can accommodate any number of lines.

CGSize maximumSize = CGSizeMake(300, 9999);
NSString *dateString = @"The date today is January 1st, 1999";
UIFont *dateFont = [UIFont fontWithName:@"Helvetica" size:14];
CGSize dateStringSize = [dateString sizeWithFont:dateFont 
        constrainedToSize:maximumSize 
        lineBreakMode:self.dateLabel.lineBreakMode];

CGRect dateFrame = CGRectMake(10, 10, 300, dateStringSize.height);

self.dateLabel.frame = dateFrame;