iOS-關於自定義分段選擇器的一些小事（Segmented）

系統自帶的分段選擇就是 UISegmentedControl ，也有一些大佬自定義的 Segmented ，比如Git上的 HMSegmentedControl ，我以前最初的項目中，也有用到過，如果自己寫，或者想自定義一些UI，該從哪裡出發，其實在用過 HMSegmentedControl 之後，大致就有思路了，如果想簡單的實現下，可以利用 UICollectionView 來實現，下麵是我利用 UICollectionView 寫的一個簡單的小慄子，效果圖

設計思路

首先利用 UICollectionView 處理每個item的大小，確切的說是寬度，那麼就要每次選中一個item後，重新計算所有的item的寬度，同時計算 UICollectionView 的 contentSize.width；

計算每個item寬度分為兩種情況，一種是選中的字體的顯示，一種是未選中的字體顯示，比如字體大小，顏色等，然後根據字體大小字元串長度，計算出字體需要展示的寬度，並計算對應的item寬度，最後把每個item的寬度保存起來，用於在 UICollectionView 代理方法中做處理；

計算 contentSize.width 由上圖可知，是由兩邊的間距，item之間的間距和每個item的總和，目的是利用 contentSize.width 計算下劃線的位置；

具體實現

#import "XKCollectionView.h"

///四周邊距
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>
///臨時數據
@property (nonatomic,strong) NSArray<NSString *> *titleArray;
///每個item的寬度
@property (nonatomic,strong) NSMutableArray *widthsArray;
///底部線條
@property (nonatomic,strong) UIView *lineView;
///選中的item索引
@property (nonatomic,assign) NSInteger selectIndex;
///選中的item string
@property (nonatomic,strong) NSString *selectString;
////計算出來的總寬度，用於設置 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 = @[@"一級建造師",@"二級建造師",@"造價工程師",@"咨詢工程師",@"註冊安全工程師",@"監理工程師",@"註冊電氣工程師",@"環境影響評價工程師",@"註冊城鄉規劃師",@"註冊消防工程師"];
    [self storeSegmentedWidth];
    [self reloadData];
    CGRect lineRext = [self measureLineFrame];
    self.lineView.frame = lineRext;
    ///設置偏移量
    [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 ========== 儲存計算好的item寬度 ==========
///每次切換時更新
- (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 ========== 計算下劃線位置 ==========
- (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 ========== 計算偏移量 ==========
- (CGFloat)measureContentOffsetX{
    CGFloat selfWidth = self.bounds.size.width;
    
    ///先計算點擊的item中心點
    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) {///充滿內部不做偏移
        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 ========== 變數 ==========

- (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