带有约束和 RTL 的 UIScrollView 的奇怪行为

Question

我有一个水平滚动视图，我在其上动态添加视图。 在 LTR 语言上一切正常，我从左到右一个接一个地添加视图。 在 RTL 上，问题是视图总是添加到滚动的左侧，而不是像其他控制器一样添加到右侧，真的奇怪的员工认为视图的顺序被正确添加到在第一个视图的左侧，因此它们从右到左排序，但在 -x 上的滚动视图之外。

这是我添加新视图时的代码：

Tag* tag = [self.storyboard instantiateViewControllerWithIdentifier:@"tag" ];
[_scroller addSubview:tag.view];
[tags addObject:tag];
Tag* prev = nil
for (Tag* tag in tags)
{
    if (prev == nil)
    {
        [_scroller addConstraint:[NSLayoutConstraint constraintWithItem:tag.view 
                                                       attribute:NSLayoutAttributeLeading                                                                                          
                                                       relatedBy:NSLayoutRelationEqual
                                                                     toItem:_scroller
                                                                  attribute:NSLayoutAttributeLeading
                                                                 multiplier:1.0f
                                                                   constant:0]];
    }
    else
    {
        [_scroller addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"[prev]-10-[tag]"
                                                                          options:0
                                                                          metrics:nil
                                                                            views:@{@"tag" : tag.view, @"prev" : prev.view}]];
    }

    [_scroller addConstraint:[NSLayoutConstraint constraintWithItem:tag.view
                                                          attribute:NSLayoutAttributeCenterY
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:_scroller
                                                          attribute:NSLayoutAttributeCenterY
                                                             multiplier:1.0f
                                                               constant:0]];
    prev = tag;

}

这是它假设如何在 LTR 和 RTL 上工作以及它实际上是如何工作的图片

Answer 1

UIScrollView 出现这种行为的原因是您忘记将最后一个元素 (#4) 的 trailingAnchor 附加到滚动视图的 trailingAnchor。

滚动视图和元素#1 的leadingAnchor 相互连接（见下文绿色部分）。然而，滚动视图的内容矩形自然地跨越到正坐标方向，从原点(0,0) 到右，向下(+x, +y)。在您的情况下，滚动视图的内容大小为宽度 0，因为滚动视图的 leadingAnchor 和 trailingAnchor 之间没有任何内容。

所以在你的[_scroller addConstraints:_constraint];下面添加类似（伪代码）：

if tag == lastTag {
  NSLAyoutconstraints.activate([
    tag.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor)
  ])
}

Answer 2

听起来更好的方法可能是使用UICollectionView。然后，如果您想从右侧启动它，您可以执行以下操作：

NSIndexPath *lastIndex = [NSIndexPath indexPathForItem:data.count - 1 
                                             inSection:0];
[self.collectionView scrollToItemAtIndexPath:lastIndex 
                            atScrollPosition:UICollectionViewScrollPositionRight 
                                    animated:NO];

这样UICollectionViewFlowLayout 可以为您处理展示位置。

Answer 3

这是我的示例代码。

//
//  ViewController.m
//  testConstraint
//
//  Created by stevenj on 2014. 3. 24..
//  Copyright (c) 2014년 Steven Jiang. All rights reserved.
//

#import "ViewController.h"


@interface TagView : UILabel
- (void)setNumber:(NSInteger)num;
@end

@implementation TagView

- (void)setNumber:(NSInteger)num
{
    [self setText:[NSString stringWithFormat:@"%d",num]];
}

@end

@interface ViewController ()

@property (nonatomic, strong) UIScrollView *scroller;
@property (nonatomic, strong) NSMutableArray *tags;
@property (nonatomic, strong) NSMutableArray *constraint;

@end

@implementation ViewController

@synthesize scroller = _scroller;

- (void)viewDidLoad
{
    [super viewDidLoad];
    _tags = [NSMutableArray new];
    _constraint = [NSMutableArray new];
    // Do any additional setup after loading the view, typically from a nib.

    //step.1 create scroll view
    _scroller = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 20, 320, 60)];
    [_scroller setBackgroundColor:[UIColor lightGrayColor]];
    [_scroller removeConstraints:[_scroller constraints]];
    [_scroller setTranslatesAutoresizingMaskIntoConstraints:YES];

    [self.view addSubview:_scroller];


    //step.2 add tag view
    for (int i=0; i<10; i++) {
        TagView *tag = [[TagView alloc] init];

        [tag setFrame:CGRectMake(100, 30, 50, 30)];
        [tag setNumber:i];

        [tag.layer setBorderWidth:1.0];
        [tag setTranslatesAutoresizingMaskIntoConstraints:NO];

        [_scroller addSubview:tag];
        [_tags addObject:tag];
    }

    //step.3 update contraints
    [self myUpdateConstraints];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)myUpdateConstraints
{
    [_constraint removeAllObjects];

    TagView* prev = nil;
    for (TagView* tag in _tags)
    {
        [tag setNumber:[_tags indexOfObject:tag]];

        if (prev == nil)
        {

            [_constraint addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-(<=300)-[tag]-20-|"
                                                                                     options:NSLayoutFormatDirectionLeadingToTrailing
                                                                                     metrics:nil
                                                                                       views:@{@"tag" : tag}]];
        }
        else
        {
            [_constraint addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"[tag]-10-[prev]"
                                                                              options:0
                                                                              metrics:nil
                                                                                views:@{@"tag" : tag, @"prev" : prev}]];

        }

        [_scroller addConstraint:[NSLayoutConstraint constraintWithItem:tag
                                                              attribute:NSLayoutAttributeCenterY
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:_scroller
                                                              attribute:NSLayoutAttributeCenterY
                                                             multiplier:1.0f
                                                               constant:0]];

        prev = tag;

    }
    [_scroller addConstraints:_constraint];
}
@end

希望对你有帮助。

Answer 4

试试这个

#import "ViewController.h"

@interface ViewController ()<UIScrollViewDelegate>
{
UIView *baseView;
UILabel *titleLabel;
NSMutableArray *infoArray ;
UIScrollView *mainscrollview;
}
@end

@implementation ViewController

- (void)viewDidLoad
{
[super viewDidLoad];

infoArray =[[NSMutableArray alloc]initWithObjects:@"1",@"2",@"3", nil];
   NSLog(@"%@",infoArray);
mainscrollview=[[UIScrollView alloc]initWithFrame:CGRectMake(0, 0, 320, 380)];
mainscrollview.delegate=self;
mainscrollview.contentSize=CGSizeMake(320*infoArray.count, 0);
[self.view addSubview:mainscrollview];
[self sscrollcontent:@"LTR"];//LTR for Lefttoright other than LTR it will show RTL
}
-(void)sscrollcontent:(NSString *)flowtype
{
int xaxis=0;
for (int i=0; i<infoArray.count; i++) {
    baseView=[[UIView alloc]initWithFrame:CGRectMake(xaxis, 0, 320, 380)];
    [mainscrollview addSubview:baseView];
    titleLabel =[[UILabel alloc]initWithFrame:CGRectMake(0, 0, 320, 60)];
    titleLabel.textAlignment=NSTextAlignmentCenter;
    if ([flowtype isEqualToString:@"LTR"]) {
        titleLabel.text=infoArray[i];

    }
    else
    {
        titleLabel.text=infoArray[infoArray.count-i-1];

    }
    [baseView addSubview:titleLabel];
    xaxis=xaxis+320;
}
}

@end

希望对你有帮助