使用 NSAttributedString 滚动 UITextView 不正确

Question

我想制作一个同步的显示歌词应用程序，并在UITextView上显示所有歌词。为了突出当前的歌词，我为UITextView NSAttributedString添加了背景色。存储在NSArray中的所有行NSRange。

我的代码非常简单，当点击按钮时，突出显示行向下移动（通过UITextView的设置内容偏移量）。但是这里出现了一个奇怪的问题。一开始，UITextView正确滚动，但是当contentOffset UITextView大于其frame.size.height时，它被修复了。

这是我的代码：

//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:@"rn"];
    __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

我所有的代码都在ViewController中，StoryBoard有两个UIButton和一个UITextView。我想知道的是"为什么UITextView.contentOffset在大于某个大小时不能更改"。

Answer 1

也许重写setContentOffset:animated对您有帮助！

以下是一些可以借用的示例代码：
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