Incorrect scrolling UITextView with NSAttributedString - ios

Question

I want to make a synchronized show lyric app and all lyric shown on a UITextView. In order to highlight current lyric I add background color to NSAttributedString of UITextView. All NSRange of lines stored in a NSArray.
My code is pretty simple, when button tapped move the highlight line down (via set contentOffset of UITextView). But here a strange problem occurred. In the beginning, the UITextView scroll properly but when contentOffset of UITextView greater then its frame.size.height it was fixed.
Here is my code:
//View controller
#import "ViewController.h"
#interface ViewController () {
NSUInteger globelIndex;
NSArray *textRanges;
NSMutableAttributedString *attributedText;
}
#property (weak, nonatomic) IBOutlet UITextView *lyricView;
#property (strong, nonatomic) NSTimer *mainTimer;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
NSString *rawText = [self readFile];
globelIndex = 0;
[self initTextLines:rawText];
attributedText = [[NSMutableAttributedString alloc] initWithString:rawText
attributes:#{NSBackgroundColorAttributeName: [UIColor orangeColor]}];
self.lyricView.attributedText = [attributedText copy];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)manualNextLine:(UIButton *)sender {
[self updateTextView];
}
- (IBAction)autoNextLineUsingNSTimer:(UIButton *)sender {
self.mainTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(updateTextView) userInfo:nil repeats:YES];
}
- (void)updateTextView {
if (self.lyricView.contentOffset.y >= self.lyricView.contentSize.height &&
self.mainTimer)
{
self.mainTimer = nil;
return;
}
NSMutableAttributedString *mat = [attributedText mutableCopy];
NSValue *value = [textRanges objectAtIndex:globelIndex];
[mat addAttribute:NSBackgroundColorAttributeName value:[UIColor whiteColor] range:[value rangeValue]];
self.lyricView.attributedText = [mat copy];
globelIndex += 1;
// self.textView.contentOffset = CGPointMake(self.textView.contentOffset.x, self.textView.contentOffset.y + 24);
// [self.textView scrollRangeToVisible:[value rangeValue]];
CGPoint newOffset = CGPointMake(self.lyricView.contentOffset.x, self.lyricView.contentOffset.y + 20);
[self.lyricView setContentOffset:newOffset animated:NO];
NSLog(#"[%# %#] h: %f b: %f a: %f", NSStringFromClass([self class]), NSStringFromSelector(_cmd), self.lyricView.contentSize.height, newOffset.y, self.lyricView.contentOffset.y);
}
#pragma mark - helper
- (void)initTextLines:(NSString *)rawText {
NSMutableArray *result = [#[] mutableCopy];
NSArray *t = [rawText componentsSeparatedByString:#"\r\n"];
__block int index = 0;
[t enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
NSString *s = obj;
NSRange range = NSMakeRange(index, s.length + 2);
[result addObject:[NSValue valueWithRange:range]];
index += s.length + 2;
}];
textRanges = [result copy];
}
- (NSString *)readFile {
NSError *error = nil;
NSURL *fileURL = [[NSBundle mainBundle] URLForResource:#"二人の季節が-ささきのぞみ-想い" withExtension:#"lrc"];
NSString *content = [NSString stringWithContentsOfURL:fileURL encoding:NSUTF8StringEncoding error:&error];
if (error) {
if (DEBUG) NSLog(#"[%# %#] Error: %#", NSStringFromClass([self class]), NSStringFromSelector(_cmd), error.localizedDescription);
abort();
}
return content;
}
#end
All my code was in ViewController and StoryBoard has two UIButton and a UITextView.
What I wonder is "Why the UITextView.contentOffset cannot change when it greater than some size".

Answer 1

Maybe rewrite setContentOffset:animated is helpful for you!
Here is some sample code which you can borrow:
https://github.com/360/Three20/blob/master/src/Three20UI/Sources/TTTextView.m
#import "Three20UI/TTTextView.h"
// UI
#import "Three20UI/UIViewAdditions.h"
#implementation TTTextView
#synthesize autoresizesToText = _autoresizesToText;
#synthesize overflowed = _overflowed;
- (void)setContentOffset:(CGPoint)offset animated:(BOOL)animated {
if (_autoresizesToText) {
if (!_overflowed) {
// In autosizing mode, we don't ever allow the text view to scroll past zero
// unless it has past its maximum number of lines
[super setContentOffset:CGPointZero animated:animated];
} else {
// If there is an overflow, we force the text view to keep the cursor at the bottom of the
// view.
[super setContentOffset: CGPointMake(offset.x, self.contentSize.height - self.height)
animated: animated];
}
} else {
[super setContentOffset:offset animated:animated];
}
}
#end