在Swift 4或Swift 5中，你可以使用like bellow:

let date = Date()
let yesterday = Calendar.current.date(byAdding: .day, value: -1, to: date)
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let yesterday_date = dateFormatter.string(from: yesterday!)
print("yesterday->",yesterday_date)

输出:

Current date: 2020-03-02
yesterday date: 2020-03-01

简单的Swift扩展昨天和明天从任何日期:

extension Date {
    
    var previousDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:-1), to: self)!
    }
    
    var nextDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:+1), to: self)!
    }
    
}

我在这里根据问题中的建议强制展开可选选项: 何时dateByAddingComponents:toDate:options返回nil?

这是一个通用的方法，它允许您在指定的日期中添加/减去任何类型的单位(年/月/日/小时/秒等)。

使用Swift 2.2

func addUnitToDate(unitType: NSCalendarUnit, number: Int, date:NSDate) -> NSDate {

    return NSCalendar.currentCalendar().dateByAddingUnit(
        unitType,
        value: number,
        toDate: date,
        options: NSCalendarOptions(rawValue: 0))!

}

print( addUnitToDate(.Day, number: 1, date: NSDate()) ) // Adds 1 Day To Current Date
print( addUnitToDate(.Hour, number: 1, date: NSDate()) ) // Adds 1 Hour To Current Date
print( addUnitToDate(.Minute, number: 1, date: NSDate()) ) // Adds 1 Minute To Current Date

// NOTE: You can use negative values to get backward values too

NSDate *now = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:now];
NSDate *startDate = [calendar dateFromComponents:components];
NSLog(@"StartDate = %@", startDate);

components.day += 1;
NSDate *endDate = [calendar dateFromComponents:components];
NSLog(@"EndDate = %@", endDate);

在Swift 4或Swift 5中，你可以使用like bellow:

let date = Date()
let yesterday = Calendar.current.date(byAdding: .day, value: -1, to: date)
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let yesterday_date = dateFormatter.string(from: yesterday!)
print("yesterday->",yesterday_date)

输出:

Current date: 2020-03-02
yesterday date: 2020-03-01

Swift 3.0非常简单的实现将是:

func dateByAddingDays(inDays: Int) -> Date {
    let today = Date()
    return Calendar.current.date(byAdding: .day, value: inDays, to: today)!
}