Ios 在UITextView中查找可见文本的范围

我从前面问题的答案中找到了计算UITextView中可见属性文本范围的代码。它工作得很好，除非我添加了任何类型的换行符以创建新段落。在这种情况下，代码给出了不正确的答案，直到我手动滚动视图。滚动后，每次都会给出正确答案。但我需要它给出正确的答案，即使没有滚动

下面是我的示例项目。它是一个单视图应用程序。程序在日志中报告它认为可见的文本，第一次加载视图，然后滚动

ViewController.h

#导入
@界面ViewController:UIViewController{
UITextView*lTextView；
}
@结束

ViewController.m

#导入“ViewController.h”
@界面视图控制器（）
@结束
@实现视图控制器
-（无效）viewDidLoad{
[超级视图下载]；
int statusBarHeight=20；
UIScrollView*滚动视图；
scrollView=[[UIScrollView alloc]initWithFrame:CGRectMake（0，statusBarHeight，self.view.frame.size.width*2，self.view.frame.size.height）]；
scrollView.PaginEnabled=是；
scrollView.delegate=self；
[self.view addSubview:scrollView]；
lTextView=[[UITextView alloc]initWithFrame:CGRectMake（0,0，scrollView.frame.size.width/2，scrollView.frame.size.height）]；
lTextView.editable=否；
lTextView.selective=否；
lTextView.attributeText=[self-loremIpsum]；
[滚动视图添加子视图：lTextView]；
lTextView.delegate=self；
[自我报告]；
}
-（作废）报告{
NSArray*visibleRange=[self-visibleRangeOfTextView:lTextView]；
NSNumber*start=[visibleRange objectAtIndex:0]；
NSNumber*end=[visibleRange对象索引：1]；
int rangeLength=（end.intValue-start.intValue）；
NSLog（@“%@，[lTextView.text substringWithRange:NSMakeRange（start.intValue，rangeLength）]）；
}
-（NSArray*）visibleRangeOfTextView:（UITextView*）textView{
CGRect bounds=textView.bounds；
bounds.size.height-=30.0；//防止包含在底部几乎看不见的线条
UITextPosition*start=[textView characterRangeAtPoint:bounds.origin].start；
UITextPosition*end=[textView characterRangeAtPoint:CGPointMake（CGRectGetMaxX（边界），CGRectGetMaxY（边界））].end；//听起来好像API中的UI信息不是最新的。只要您滚动UI信息就会更新。您要寻找的是一种在新数据发生更改时立即检索新数据的方法。请尝试调用layoutIfNeeded，然后再尝试找出可见属性文本的范围。
调用“report”在委托函数“textView:DiDendededid:”

当然，您已经设置了TextView的委托：

self.textView.delegate = self;

并声明委托协议。
该问题是由于试图过早地确定visibleRange引起的

UI更改的实际效果并不总是立即发生。相反，UIKit可以延迟一些工作，直到完成主线程

在提供的示例代码中，
lTextView
被添加到
scrollView
中，然后在同一执行线程上计算visibleRange。额外的UIKit工作尚未完成

将
[self report]
调用异步发送回主线程。
ViewDidLoad
将完成，放弃主线程。UIKit将有机会完成，您现在应该可以返回正确的可视范围

在
viewDidLoad
中，更改：

[self report];

致：

在
-viewDidLoad
，
self.view
实际上还不在视图层次结构中。

因此，
UITextView
的
-drawRect
尚未调用。

我想这就是为什么
-offsetFromPosition:
无法计算的原因

试试这个：

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"viewDidAppear");
    [self report];
}

如果要立即强制
UITextView
布局，请尝试：

[[lTextView layoutManager] ensureLayoutForTextContainer:[lTextView textContainer]];

在我添加赏金的那天，我提出了一个解决方案，但没有发布它，这样其他人就有机会发布对其他人有用的东西。Bajorek先生和rintaro先生都发布了有效的答案。我的解决方案有点不同；它更适合我在项目中尝试做的事情（因为我将使用多个UITextView）。它禁用UITextView中的滚动，让UIScrollView处理滚动，并将UITextView添加为容纳所有属性文本所需的完整高度。这允许计算从一开始就正常工作

为了以后可能阅读的其他人的利益，我在下面发布了一个完整的工作示例。我将此标记为已接受的答案，因为这是我在发布其他解决方案之前所走的路线

ViewController.h

#导入
@界面ViewController:UIViewController{
UITextView*lTextView；
UIScrollView*滚动视图；
}
@结束

ViewController.m

#导入“ViewController.h”
@界面视图控制器（）
@结束
@实现视图控制器
-（无效）viewDidLoad{
[超级视图下载]；
int statusBarHeight=20；
scrollView=[[UIScrollView alloc]initWithFrame:CGRectMake（0，statusBarHeight，self.view.frame.size.width，self.view.frame.size.height）]；
[self.view addSubview:scrollView]；
lTextView=[[UITextView alloc]init]；
lTextView.editable=否；
lTextView.selective=否；
lTextView.scrollEnabled=否；
lTextView.textContainerSet=UIEdgeInSetZero；
lTextView.attributeText=[self-loremIpsum]；
float calculatedHeight=[AttributedText:lTextView和width:scrollView.frame.size.width]的文本视图自高；
lTextView.frame=CGRectMake（0，0，scrollView.frame.size.width，calculatedHeight）；
[滚动视图添加子视图：lTextView]；
[scrollView setContentSize:CGSizeMake（scrollView.frame.size.width，calculatedHeight+20）]；
scrollView.delegate=self；
[自我报告]；
}
-（作废）报告{
NSArray*visib
[self report];

dispatch_async(dispatch_get_main_queue(), ^{
    [self report];
});

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"viewDidAppear");
    [self report];
}

[[lTextView layoutManager] ensureLayoutForTextContainer:[lTextView textContainer]];

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UIScrollViewDelegate> {
    UITextView *lTextView;
    UIScrollView *scrollView;
}
@end

#import "ViewController.h"

@interface ViewController ()


@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    int statusBarHeight = 20;

    scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, statusBarHeight, self.view.frame.size.width, self.view.frame.size.height)];
    [self.view addSubview:scrollView];

    lTextView = [[UITextView alloc] init];
    lTextView.editable = NO;
    lTextView.selectable = NO;
    lTextView.scrollEnabled = NO;
    lTextView.textContainerInset = UIEdgeInsetsZero;

    lTextView.attributedText = [self loremIpsum];
    float calculatedHeight = [self heightForTextViewWithAttributedText:lTextView andWidth:scrollView.frame.size.width];
    lTextView.frame = CGRectMake(0, 0, scrollView.frame.size.width, calculatedHeight);
    [scrollView addSubview:lTextView];

    [scrollView setContentSize:CGSizeMake(scrollView.frame.size.width, calculatedHeight + 20)];
    scrollView.delegate = self;

    [self report];
}

- (void)report {
    NSArray *visibleRange = [self visibleRangeOfTextView:lTextView];
    NSNumber *start = [visibleRange objectAtIndex:0];
    NSNumber *end = [visibleRange objectAtIndex:1];
    int rangeLength = (end.intValue - start.intValue);

    NSLog(@"%@", [lTextView.text substringWithRange:NSMakeRange(start.intValue, rangeLength)]);

}


-(NSArray *)visibleRangeOfTextView:(UITextView *)textView {
    double offsetY = scrollView.contentOffset.y;
    CGPoint startingPoint = scrollView.contentOffset;
    startingPoint.y += 5; // to prevent including lines that can barely be seen at the top
    CGPoint endingPoint = CGPointMake(320, offsetY + scrollView.frame.size.height - 20);

    CGRect bounds = textView.bounds;
    bounds.size.height -= 30.0; // to prevent including lines that can barely be seen at the bottom

    UITextPosition *start = [textView characterRangeAtPoint:startingPoint].start;
    UITextPosition *end = [textView characterRangeAtPoint:endingPoint].end;

    float startOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:start];
    float endOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:end];

    return [NSArray arrayWithObjects:[NSNumber numberWithFloat:startOffset], [NSNumber numberWithFloat:endOffset], nil];
}


- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    NSLog(@"scrollViewDidEndDecelerating");
    [self report];
}


- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    NSLog(@"scrollViewDidEndDragging");
    [self report];
}


- (NSAttributedString *)loremIpsum {

    NSMutableAttributedString *li = [[NSMutableAttributedString alloc] init];
    NSArray *strings = [NSArray arrayWithObjects:@"1 Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam congue eleifend risus eget pretium. Donec sed commodo neque, id ornare dolor.", @" 2 Vivamus vestibulum non quam et euismod. Morbi et dolor luctus velit lobortis ornare vel vel tellus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Aenean viverra, urna nec tempor commodo, turpis nisl rhoncus mauris, in ullamcorper justo sapien quis nulla.", @" 3 Aliquam at odio molestie, laoreet elit sed, suscipit risus. Nulla eleifend, quam eget porttitor condimentum, metus lacus lobortis ligula, accumsan tristique neque turpis non purus. Aenean malesuada tortor id elit semper, et pretium nulla viverra.", @" 4 Aliquam sollicitudin placerat massa, quis posuere est ornare vel. Nam mollis convallis risus a tincidunt. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos.", @" 5 Fusce facilisis orci nisi, vel egestas metus tristique vitae. Proin nec malesuada dolor. Donec eget felis accumsan, facilisis turpis vitae, blandit lacus.", @" 6 Pellentesque auctor nisl quis turpis commodo lacinia. In sed euismod urna. Praesent sed commodo magna.", @" 7 Ut interdum dignissim urna, nec feugiat dolor. Nulla facilisi. Donec fermentum mauris at ante tincidunt, id accumsan eros lacinia.", @" 8 Suspendisse potenti. Integer ac mattis eros, sed volutpat dui. Pellentesque vehicula turpis ut metus malesuada blandit.", @" 9 Nam laoreet dui id imperdiet pulvinar. In auctor enim ac massa feugiat adipiscing. Nam convallis neque at felis tincidunt iaculis. Maecenas dictum est ac nulla suscipit, nec condimentum metus molestie.", @" 10 Vestibulum mollis velit eu nunc eleifend egestas. Ut aliquam ultrices tellus volutpat consectetur. Morbi eget sollicitudin quam, ut imperdiet leo. Morbi sed ligula iaculis, tincidunt diam nec, pharetra ligula.", @" 11 Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Proin varius facilisis placerat. Fusce suscipit risus risus, in varius diam convallis quis. In hac habitasse platea dictumst. Integer non lectus non dolor fringilla venenatis eget quis nisl. Proin in pretium metus.", @" 12 Pellentesque sed tellus iaculis, bibendum neque vel, porta ante. Phasellus eu vulputate massa. Nullam venenatis lectus non nunc aliquet porta. Nunc gravida rutrum feugiat. Fusce elit nunc, facilisis non tristique placerat, tempor id orci. Mauris et massa cursus, dapibus urna a, condimentum arcu. Pellentesque vitae sagittis sapien. Ut lacus purus, suscipit at magna non, rhoncus luctus dui. Ut ipsum augue, pharetra ac ipsum sed, facilisis convallis justo.", @" 13 Ut arcu augue, hendrerit vel tincidunt vitae, aliquet ac quam. Nulla ullamcorper, dolor eu pellentesque cursus, lectus quam interdum ante, nec congue dui augue nec dolor. Sed convallis elit in enim dictum, at posuere sem mollis. Praesent in metus aliquam, ullamcorper purus tempor, mattis ipsum. Aliquam gravida, sem vitae iaculis placerat, dui velit commodo nulla, vitae ultrices lectus dolor ut mi.", @" 14 Suspendisse quis metus varius, congue turpis vitae, viverra nunc. Duis placerat, felis et laoreet pretium, nibh lorem pulvinar turpis, eu euismod arcu libero at mauris. Sed laoreet, eros in tempor accumsan, odio augue fermentum dui, a pharetra felis libero eu ligula.", @"Suspendisse ultricies pulvinar urna. Donec placerat nulla non elit vestibulum mattis.", @"Phasellus semper sem a sem dignissim tempus. Sed scelerisque sed purus interdum rhoncus. Sed gravida eros sit amet dui fermentum rutrum. Proin a arcu scelerisque, volutpat orci quis, dignissim neque. Aliquam erat volutpat. Sed eget scelerisque neque.", nil];
    for (int i = 0;  i < strings.count;  i++) {
        NSString *string = [strings objectAtIndex:i];
        if (i != 0) {
            // Comment this line and it will work perfectly:
            [li appendAttributedString:[[NSAttributedString alloc] initWithString:@"\n\n"]];
        }
        [li appendAttributedString:[[NSAttributedString alloc] initWithString:string]];
    }
    return li;
}


- (CGFloat)heightForTextViewWithAttributedText:(UITextView *)textView andWidth:(CGFloat)width
{
    CGSize size = [textView sizeThatFits:CGSizeMake(width, FLT_MAX)];
    return size.height + 3.0;
}
@end