Setting maximum number of lines entry on UITextView

Question

I would like to restrict the user of my iPad app to entering a maximum of 20 lines when outputted on the pdf. The user enters text into the UITextView (as shown below) and this is then later converted into a pdf document.

I realise that I will have to do a few of calculations depending on what text is entered as they type. Are there any methods that can help me out here? textFieldDidEndEditing only allows me to check after it has been entered.

Also, as this would be far simpler, is there a way of limiting the number of lines a UITextField can be?

Answer 1

You were close with the textFieldDidEndEditing delegate method.

A better way though is to respond to the textView:shouldChangeTextInRange:replacementText: delegate method and then see if the change that is about to happen would result in more lines that are allowed.

Here is an example on how to do that:

- (BOOL) textView:(UITextView *)textView
    shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
    static const NSUInteger MAX_NUMBER_OF_LINES_ALLOWED = 3;

    NSMutableString *t = [NSMutableString stringWithString:
        self.textView.text];
    [t replaceCharactersInRange: range withString: text];

    NSUInteger numberOfLines = 0;
    for (NSUInteger i = 0; i < t.length; i++) {
        if ([[NSCharacterSet newlineCharacterSet]
                characterIsMember: [t characterAtIndex: i]]) {
            numberOfLines++;
        }
    }

    return (numberOfLines < MAX_NUMBER_OF_LINES_ALLOWED);
}

I put a complete example online at https://github.com/st3fan/StackOverflow/tree/master/TextViewWithLineLimit .. tested on iOS 7.0.2. Enjoy!

Answer 2

The following works with '\n' + wrapped line support.

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.AutoresizingMask   = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        self.AutocorrectionType = UITextAutocorrectionTypeNo;
        self.KeyboardAppearance = UIKeyboardAppearanceAlert;
        self.font               = [UIFont fontWithName:@"Avenir" size:14];

        self.maximumNumberOfLinesAllowed = 4;

        self.delegate           = self;
    }

    return self;
}


- (BOOL)textView:(UITextView *)aTextView shouldChangeTextInRange:(NSRange)aRange replacementText:(NSString*)aText
{
    NSMutableString *t = [NSMutableString stringWithString: self.text];
    [t replaceCharactersInRange: aRange withString: aText];

    // First check for standard '\n' (newline) type characters.
    NSUInteger numberOfLines = 0;
    for (NSUInteger i = 0; i < t.length; i++) {
        if ([[NSCharacterSet newlineCharacterSet] characterIsMember: [t characterAtIndex: i]]) {
            numberOfLines++;
        }
    }

    if (numberOfLines >= self.maximumNumberOfLinesAllowed)
        return NO;


    // Now check for word wrapping onto newline.
    NSAttributedString *t2 = [[NSAttributedString alloc]
                             initWithString:[NSMutableString stringWithString:t] attributes:@{NSFontAttributeName:self.font}];

    __block NSInteger lineCount = 0;

    CGFloat maxWidth   = self.frame.size.width;
    NSLog(@"maxWidth = %.02f", maxWidth);

    NSTextContainer *tc = [[NSTextContainer alloc] initWithSize:CGSizeMake(maxWidth, CGFLOAT_MAX)];
    NSLayoutManager *lm = [[NSLayoutManager alloc] init];
    NSTextStorage   *ts = [[NSTextStorage alloc] initWithAttributedString:t2];
    [ts addLayoutManager:lm];
    [lm addTextContainer:tc];
    [lm enumerateLineFragmentsForGlyphRange:NSMakeRange(0,lm.numberOfGlyphs)
                                 usingBlock:^(CGRect rect,
                                              CGRect usedRect,
                                              NSTextContainer *textContainer,
                                              NSRange glyphRange,
                                              BOOL *stop)
     {
         lineCount++;
     }];

//    NSLog(@"%d", lineCount);

    return (lineCount <= self.maximumNumberOfLinesAllowed);

}