Road To iOS series 1

Attributed String & UITextView in Objective-C

What is Attributed String

Determine how text will render on the screen. You can think of NSAttributedString as an NSString where each character has an NSDictionary of “attributes”.

// this will create a dictionary for holding diifferent standard attributes
// the name of attributes are global NSString constants
NSDictionary *attrsDictionary =
	// specify font attributes
	@{ NSFontAttributeName :
	     [UIFont preferredFontWithTextStyle:UIFontTextStyleHeadline],
	// specify foreground attribute
	  NSForegroundColorAttributeName : [UIColor greenColor],
	  NSStrokeWidthAttributeName : @-5,
	  NSStrokeColorAttributeName : [UIColor redColor] }
// creating attributed string using attribute dictionary
NSAttributedString *attrString =
	[[NSAttributedString alloc] initWithString:@"string" attributes:attrsDictionary];

What is NSRange

To specify subranges inside strings and arrays. It’s a c structure defined as below:

typedef struct _NSRange {
	  // The start index (0 is the first, as in C arrays).
      NSUInteger location;
      // The number of items in the range (can be 0).
      NSUInteger length;
} NSRange;

NSNotFound

A value, or a constant that indicates that an item requested couldn’t be found or doesn’t exist.

NSString *heystack = @"heystack";
NSString *needle = @"hi";
// find the range of needle inside heystack
NSRange r = [heystack rangeOfString:needle];
// if fail to find, do something
if (r.location == NSNotFound) {...}

NSRangePointer

Just a NSRange * used as an method parameter

Access attributes of NSAttributedString

get the value for an attribute

- (id)attribute:(NSString *)attributeName atIndex:(NSUInteger)index
								   effectiveRange:(NSRangePointer)aRange
// attributeName: the name of standard attribute
// aRange: If you don't need this value, pass NULL
// return value: The value for the attribute named attributeName of the character at index index, or nil if there is no such attribute.

get all attributes as NSDictionary

- (NSDictionary *)attributesAtIndex:(NSUInteger)index effectiveRange:(NSRangePointer)aRange
// return value: The attributes for the character at index.
// aRange: If you don't need this value, pass NULL

Set attributes of NSAttributedString

Since NSAttributedString is immutable, we need NSMutableAttributedString to do all the settings…

// add an attribute to a range of characters
- (void)addAttributes:(NSDictionary *)attributes range:(NSRange)range;
// set attributes in a range
- (void)setAttributes:(NSDictionary *)attributes range:(NSRange)range;
// remove attribute in a range
- (void)removeAttribute:(NSString *)attributeName range:(NSRange)range;

NSAttributedString is not an NSString

It’s not a subclass of NSString, methods of NSString don’t apply for NSAttributedString. However, you can convert it to NSString using - (NSString *)string.

NSAttributedString *attributedString = ...;
NSString *substring = ...;
NSRange r = [[attributedString string] rangeOfString:substring];

UITextView

Display multiline text using custom style
selectable, editable, scrollable

Set text and attributes in UITextView using textStorage

NSTextStorage is a subclass of NSMutableAttributedString.
simply modify it and the UITextView will automatically update

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UITextView *body;
@end
// Prototype: @property (nonatomic, readonly) NSTextStorage *textStorage
[self.body.textStorage addAttributes:@{ NSStrokeWidthAttributeName : @3,
                                        NSStrokeColorAttributeName :[UIColor purpleColor]}
                               range:self.body.selectedRange];

Set font in UITextView

one thing to keep in mind, the @property (nonatomic, strong) UIFont *font; will apply a font to the entire UITextView

Mindmap for NSAttributedString

NSAttributedString Mindmap