iOS项目里，涉及到double类型是数据，经常会用到四舍五入这样的取值方式，网上查阅资料之后，经常会不起作用，最终把有效的方法，总结了一下。
OC:
/**
四舍五入字符串
@param round 小数位 eg: 2
@param numberString 数字 eg 0.125
@return 四舍五入之后的 eg: 0.13
*/
- (double )roundNumberStringWithRound:(NSInteger)round numberString:(NSString *)numberString{
if (numberString == nil) {
return 0;
}
NSDecimalNumberHandler *roundingBehavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:round raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
NSDecimalNumber *aDN = [[NSDecimalNumber alloc] initWithString:numberString];
NSDecimalNumber *resultDN = [aDN decimalNumberByRoundingAccordingToBehavior:roundingBehavior];
return resultDN.doubleValue;
}
Swift：
/// 四舍五入2位小数小数
///
/// - round: 小数位（默认2位小数）
/// - Parameter numberString: 格式化之前 eg 0.125
/// - Returns: 格式化之后 eg: 0.13
func roundNumberString(round:Int = 2, numberString : String) -> Double {
if numberString.isEmpty || round == 0 {
return 0.0
}
let roudingBehavior = NSDecimalNumberHandler(roundingMode: .plain, scale: Int16(round), raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false)
let aDn = NSDecimalNumber(string: numberString)
let resultDn = aDn.rounding(accordingToBehavior: roudingBehavior)
return resultDn.doubleValue
}
