UITextView does not fit NSTextContainer exactly

Question

I just created a custom method using a TextKit stack but am confused by what appears to be a difference between the size of NSTextContainer and the NSTextView frame size. The text has a white border and I’d like to know how to get rid of it (see update). The area following the last character is also white. I’ve set an attribute for backgroundColor using a range that matches the length of the string but so far I have not found a way to apply this attribute to the entire area.

I tried various combinations of settings for NSTextContainer and the text frame of UITextView. The following statements get closest to the desired result but the white border is still there.

    // A
    textContainer = [[NSTextContainer alloc] initWithSize:textFrame.size];

    // D 
    UITextView *textView = [[UITextView alloc] initWithFrame: textFrame textContainer: textContainer];

I worked through tutorials on TextKit here and here and searched through Apple documentation here here and here. I also checked the closest question and yes, my appDelegate has

    [self.window makeKeyAndVisible];

---

Update

The white border has been eliminated following the answer here (thanks Larme)

The following statements were added to textView at the end of the method

    textView.textContainerInset = UIEdgeInsetsZero;
    textView.textContainer.lineFragmentPadding = 0;

---

In case it’s relevant, the app was started in iOS 4. It now runs iOS 11 using Xcode Version 9.2. It already uses textView and TextKit is now being considered (reluctantly) as a way to address a number of requests from app testers. So any pointer that might help explain and fix this problem would be welcome.

Thanks in anticipation.

Here is the code for the method. helpMessage is read from an Array (not shown).

    -(id)formatHelpText:(NSString*)helpMessage
{
    float sideMargin   = 5;
    float topMargin    = 72;

    CGFloat textWidth  = [UIScreen mainScreen].bounds.size.width - (sideMargin * 2);
    CGFloat textHeight = [UIScreen mainScreen].bounds.size.height - (topMargin * 2);
    CGRect  textFrame  = CGRectMake(sideMargin, topMargin, textWidth, textHeight); // used for A & D


    NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithString:helpMessage];

// define paragraph attributes

    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    [style setLineSpacing:1.5];
    [style setAlignment:NSTextAlignmentLeft];

// use attributedText to define character attributes

    float spacing        = 0.0f;
    float baselineOffSet = 1.0f;

    [attributedText setAttributes:@{
                                NSFontAttributeName:[UIFont preferredFontForTextStyle:UIFontTextStyleBody],
                                NSBaselineOffsetAttributeName:[NSNumber numberWithFloat:baselineOffSet],
                                NSForegroundColorAttributeName:[UIColor whiteColor],
                                NSBackgroundColorAttributeName:[UIColor grayColor],
                                NSParagraphStyleAttributeName:style,
                                NSKernAttributeName:@(spacing)
                                }
                        range:range];


// TextKit - non-view

    NSTextStorage *textStorage;
    NSLayoutManager *layoutManager;
    NSTextContainer *textContainer;

    textStorage   = [[NSTextStorage alloc] initWithAttributedString:attributedText];
    layoutManager = [[NSLayoutManager alloc] init];
    textContainer = [[NSTextContainer alloc] init];

    [textStorage addLayoutManager:layoutManager];


// A
    textContainer = [[NSTextContainer alloc] initWithSize:textFrame.size];
// B 
//    textContainer = [[NSTextContainer alloc] initWithSize:[UIScreen mainScreen].bounds.size];   
    [layoutManager addTextContainer:textContainer];


// C
//    UITextView *textView = [[UITextView alloc] initWithFrame: [UIScreen mainScreen].bounds textContainer: textContainer];
// D 
    UITextView *textView = [[UITextView alloc] initWithFrame: textFrame textContainer: textContainer];


// update

    textView.textContainerInset = UIEdgeInsetsZero;
    textView.textContainer.lineFragmentPadding = 0;

    return textView;
}

Answer 1

Both problems are now solved. The white border was removed using UIEdgeInsetsZero to clear the default setting and textContainer.lineFragmentPadding = 0 (thanks, Larme). I hid the unhighlighted part of the last line of UITextView by removing background colour as a character attribute and defining it instead as a property of textView. sizeToFit is added to minimise the number of lines in textView. Here is the final code

#import "HelpTextView.h"

@implementation HelpTextView

-(id)formatHelpText:(NSString*)helpMessage
{
    float sideMargin   = 5;
    float topMargin    = 72;

    CGFloat textWidth  = [UIScreen mainScreen].bounds.size.width - (sideMargin * 2);
    CGFloat textHeight = [UIScreen mainScreen].bounds.size.height - (topMargin * 2);
    CGRect  textFrame  = CGRectMake(sideMargin, topMargin, textWidth, textHeight);

    NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithString:helpMessage];

    // define paragraph attributes

    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    [style setLineSpacing:0.5];
    [style setAlignment:NSTextAlignmentLeft];

    float spacing = 0.0f;
    float baselineOffSet = 1.0f;
    NSRange range = (NSRange){0,[attributedText length]};

    // use attributedText to define character attributes

    [attributedText setAttributes:@{
                                NSFontAttributeName:[UIFont preferredFontForTextStyle:UIFontTextStyleBody],
                                NSBaselineOffsetAttributeName:[NSNumber numberWithFloat:baselineOffSet],
                                NSForegroundColorAttributeName:[UIColor whiteColor],
                                NSParagraphStyleAttributeName:style,
                                NSKernAttributeName:@(spacing)
                                }
                        range:range];

    NSTextStorage* textStorage = [[NSTextStorage alloc] initWithAttributedString:attributedText];
    NSLayoutManager *layoutManager = [NSLayoutManager new];
    [textStorage addLayoutManager:layoutManager];

    CGSize containerSize = CGSizeMake(textFrame.size.width, CGFLOAT_MAX);
    NSTextContainer *textContainer = [[NSTextContainer alloc] initWithSize:containerSize];

    [layoutManager addTextContainer:textContainer];

    UITextView *textView = [[UITextView alloc] initWithFrame: textFrame textContainer: textContainer];
    textView.textContainerInset = UIEdgeInsetsZero;
    textView.textContainer.lineFragmentPadding = 0;
    textView.editable = NO;
    textView.scrollEnabled = NO;
    textView.backgroundColor = [UIColor grayColor];
    [textView sizeToFit];

    return textView;
}