iOS-关于自定义分段选择器的一些小事（Segmented）

系统自带的分段选择就是 UISegmentedControl ，也有一些大佬自定义的 Segmented ，比如Git上的 HMSegmentedControl ，我以前最初的项目中，也有用到过，如果自己写，或者想自定义一些UI，该从哪里出发，其实在用过 HMSegmentedControl 之后，大致就有思路了，如果想简单的实现下，可以利用 UICollectionView 来实现，下面是我利用 UICollectionView 写的一个简单的小栗子，效果图

设计思路

首先利用 UICollectionView 处理每个item的大小，确切的说是宽度，那么就要每次选中一个item后，重新计算所有的item的宽度，同时计算 UICollectionView 的 contentSize.width；

计算每个item宽度分为两种情况，一种是选中的字体的显示，一种是未选中的字体显示，比如字体大小，颜色等，然后根据字体大小字符串长度，计算出字体需要展示的宽度，并计算对应的item宽度，最后把每个item的宽度保存起来，用于在 UICollectionView 代理方法中做处理；

计算 contentSize.width 由上图可知，是由两边的间距，item之间的间距和每个item的总和，目的是利用 contentSize.width 计算下划线的位置；

具体实现

#import "XKCollectionView.h"

///四周边距
const static CGFloat _margin_left = 5;
const static CGFloat _margin_right = 5;
const static CGFloat _margin_top = 0;
const static CGFloat _margin_bottom = 2;
const static CGFloat _margin_space = 15;

const static CGFloat _line_width = 30.0;
const static CGFloat _line_height = 3.0;

@interface XKCollectionView ()<UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>
///临时数据
@property (nonatomic,strong) NSArray<NSString *> *titleArray;
///每个item的宽度
@property (nonatomic,strong) NSMutableArray *widthsArray;
///底部线条
@property (nonatomic,strong) UIView *lineView;
///选中的item索引
@property (nonatomic,assign) NSInteger selectIndex;
///选中的item string
@property (nonatomic,strong) NSString *selectString;
////计算出来的总宽度，用于设置 UICollectionView.contentSize.width
@property (nonatomic,assign) CGFloat totalContentWidth;
@end
@implementation XKCollectionView
- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout{
    self = [super initWithFrame:frame collectionViewLayout:layout];
    if (self) {
        [self setup];
    }
    return self;
}
- (void)setup{
    _selectIndex = 0;
    self.widthsArray = [NSMutableArray array];
    [self addSubview:self.lineView];
    self.backgroundColor = [UIColor whiteColor];
    self.showsHorizontalScrollIndicator = NO;
    self.delegate = self;
    self.dataSource = self;
    [self registerClass:[XKCollectionViewCell class] forCellWithReuseIdentifier:@"XKCollectionViewCell"];
    
    _titleArray = @[@"一级建造师",@"二级建造师",@"造价工程师",@"咨询工程师",@"注册安全工程师",@"监理工程师",@"注册电气工程师",@"环境影响评价工程师",@"注册城乡规划师",@"注册消防工程师"];
    [self storeSegmentedWidth];
    [self reloadData];
    CGRect lineRext = [self measureLineFrame];
    self.lineView.frame = lineRext;
    ///设置偏移量
    [self setContentOffset:CGPointMake([self measureContentOffsetX], 0)];
}


- (void)updateSelectSeg{
    [self storeSegmentedWidth];
    [self reloadData];
    [UIView animateWithDuration:0.3 animations:^{
        CGRect lineRext = [self measureLineFrame];
        self.lineView.frame = lineRext;
    }];
    
    [self setContentOffset:CGPointMake([self measureContentOffsetX], 0) animated:YES];
}
#pragma mark ========== 储存计算好的item宽度 ==========
///每次切换时更新
- (void)storeSegmentedWidth{
    _selectIndex = 0;
    _totalContentWidth = 0;
    [self.widthsArray removeAllObjects];
    
    if (_selectString) {
        for (int i = 0; i < _titleArray.count; i ++) {
            NSString *title = _titleArray[i];
            if ([title isEqualToString:_selectString]) {
                _selectIndex = i;
                break;
            }
        }
    }
   
    
    for (int i = 0; i < _titleArray.count; i ++) {
        
        CGSize size = [self measureTitleIndex:i];
        NSNumber *value = [NSNumber numberWithFloat:size.width];
        [self.widthsArray addObject:value];
        
        _totalContentWidth = _totalContentWidth + size.width;
        if (i < _titleArray.count - 1) {
            _totalContentWidth = _totalContentWidth + _margin_space;
        }
    }
    _totalContentWidth = _totalContentWidth + _margin_left + _margin_right;
    
}
- (CGSize)measureTitleIndex:(NSUInteger)index {
    if (index >= _titleArray.count) {
        return CGSizeZero;
    }
    
    id title = _titleArray[index];
    CGSize size = CGSizeZero;
    BOOL selected = (index == _selectIndex);
    NSDictionary *titleAttrs = selected ? [self resultingSelectedTitleTextAttributes] : [self resultingTitleTextAttributes];
    size = [(NSString *)title sizeWithAttributes:titleAttrs];
    UIFont *font = titleAttrs[@"NSFont"];
    size = CGSizeMake(ceil(size.width), ceil(size.height - font.descender));
    CGSize resault = CGRectIntegral((CGRect){CGPointZero, size}).size;
    return resault;
}
- (NSDictionary *)resultingSelectedTitleTextAttributes {
    NSDictionary *resultingAttrs = @{NSForegroundColorAttributeName : [UIColor blackColor] ,NSFontAttributeName:[UIFont fontWithName:@"Helvetica-Bold" size:18.0]};
    return resultingAttrs;
}
- (NSDictionary *)resultingTitleTextAttributes {
    NSDictionary *resultingAttrs = @{NSForegroundColorAttributeName : [UIColor lightGrayColor],NSFontAttributeName:[UIFont systemFontOfSize:14.0]};
    return resultingAttrs;
}
#pragma mark ========== 计算下划线位置 ==========
- (CGRect)measureLineFrame{
    CGRect lineRect = CGRectZero;
    CGFloat lineRectX = 0;
    for (int i = 0; i < _selectIndex; i ++) {
        NSNumber *number = self.widthsArray[i];
        lineRectX = lineRectX + [number floatValue] + _margin_space;
    }
    CGFloat widthSelect = [self.widthsArray[_selectIndex] floatValue];
    CGFloat lastLocation = widthSelect >= _line_width ? (widthSelect - _line_width)/2 : (_line_width - widthSelect)/2;
    lineRectX = lineRectX + _margin_left + lastLocation;
    
    lineRect = CGRectMake(lineRectX, self.bounds.size.height - _line_height - 2, _line_width, _line_height);
    return lineRect;
}
#pragma mark ========== 计算偏移量 ==========
- (CGFloat)measureContentOffsetX{
    CGFloat selfWidth = self.bounds.size.width;
    
    ///先计算点击的item中心点
    CGFloat selectedCenterX = 0;
    for (int i = 0; i < _selectIndex; i ++) {
        NSNumber *number = self.widthsArray[i];
        selectedCenterX = selectedCenterX + [number floatValue] + _margin_space;
    }
    CGFloat widthSelect = [self.widthsArray[_selectIndex] floatValue];
    selectedCenterX = selectedCenterX + widthSelect/2;
    
    if (_totalContentWidth <= selfWidth) {///充满内部不做偏移
        return 0;
    }
    
    if (selectedCenterX <= selfWidth/2) {
        return 0;
    }
    else if (selectedCenterX >= _totalContentWidth - selfWidth/2){
        return _totalContentWidth - selfWidth;
    }
    else{
        return selectedCenterX - selfWidth/2;
    }
}
#pragma mark ========== 代理 ==========
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return _titleArray.count;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section{
    return _margin_space;
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
    return UIEdgeInsetsMake(_margin_top, _margin_left, _margin_bottom, _margin_right);
}
//item大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath{
    NSNumber *number = self.widthsArray[indexPath.row];
    return CGSizeMake([number floatValue],30);
}
- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    XKCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"XKCollectionViewCell" forIndexPath:indexPath];
    NSString *title = _titleArray[indexPath.row];
    cell.title = title;
    if (indexPath.row == _selectIndex) {
        cell.isSelectd = YES;
    }
    else{
        cell.isSelectd = NO;
    }
    return cell;
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    _selectString = _titleArray[indexPath.row];
    [self updateSelectSeg];
}
#pragma mark ========== 变量 ==========

- (UIView *)lineView{
    if(!_lineView){
        _lineView = [[UIView alloc]init];
        _lineView.backgroundColor = [UIColor purpleColor];
        _lineView.layer.masksToBounds = YES;
        _lineView.layer.cornerRadius = _line_height/2;
    }
    return _lineView;
}

@end