支付中最怕遇到精度有关的问题,导致金额计算不准确,我们手机端从后台接口获取数据的时候,有时候就会出现这样的问题,所以需要我们手机端对返回的数值进行精度上的转换.这里iOS给我们提供了NSDecimalNumber这个计算类,继承与NSNumber.
这里是我封装的一个方法
/**
* @brief 截取指定小数位的值
*
* @param price 目标数据
* @param position 有效小数位(一般都是两位小数)
*
* @return 截取后数据
*/
+ (NSString *)notRounding:(double)price afterPoint:(NSInteger)position
{
NSDecimalNumberHandler* roundingBehavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:position raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
NSDecimalNumber *ouncesDecimal;
NSDecimalNumber *roundedOunces;
ouncesDecimal = [[NSDecimalNumber alloc] initWithDouble:price];
roundedOunces = [ouncesDecimal decimalNumberByRoundingAccordingToBehavior:roundingBehavior];
NSString *temStr = [NSString stringWithFormat:@"%.2f", roundedOunces.doubleValue];
// NSLog(@"NSDecimalNumber----%@",temStr);
return temStr;
}
这里NSDecimalNumber 的这个初始化方法介绍一下
// Rounding policies :
// Original
// value 1.2 1.21 1.25 1.35 1.27
// Plain 1.2 1.2 1.3 1.4 1.3 四舍五入
// Down 1.2 1.2 1.2 1.3 1.2 向下取正
// Up 1.2 1.3 1.3 1.4 1.3 向上取正
// Bankers 1.2 1.2 1.2 1.4 1.3 (特殊的四舍五入，碰到保留位数后一位的数字为5时，根据前一位的奇偶性决定。为偶时向下取正，为奇数时向上取正。如：1.25保留1为小数。5之前是2偶数向下取正1.2；1.35保留1位小数时。5之前为3奇数，向上取正1.4）
typedef NS_ENUM(NSUInteger, NSRoundingMode) {
NSRoundPlain, // Round up on a tie
NSRoundDown, // Always down == truncate
NSRoundUp, // Always up
NSRoundBankers // on a tie round so last digit is even
};
//scale：保留有效小数的个数（为0的无效小数后自动过滤).
//Exactness：进度异常、Overflow:向上溢出、Underflow：向下溢出、DivideByZero：除数为0。当参数为YES出错会抛出异常，为NO时忽略异常。返回nil.
NSDecimalNumberHandler *roundUp = [NSDecimalNumberHandler
decimalNumberHandlerWithRoundingMode:NSRoundUp
scale:2
raiseOnExactness:NO
raiseOnOverflow:NO
raiseOnUnderflow:NO
raiseOnDivideByZero:YES];
其中的一些基本方法(+-*/):
NSDecimalNumber *price1 = [NSDecimalNumber decimalNumberWithString:@"15.99"];
NSDecimalNumber *price2 = [NSDecimalNumber decimalNumberWithString:@"29.99"];
NSDecimalNumber *coupon = [NSDecimalNumber decimalNumberWithString:@"5.00"];
NSDecimalNumber *discount = [NSDecimalNumber decimalNumberWithString:@".90"];
NSDecimalNumber *numProducts = [NSDecimalNumber decimalNumberWithString:@"2.0"];
NSDecimalNumber *subtotal = [price1 decimalNumberByAdding:price2];
NSDecimalNumber *afterCoupon = [subtotal decimalNumberBySubtracting:coupon];
NSDecimalNumber *afterDiscount = [afterCoupon decimalNumberByMultiplyingBy:discount];
NSDecimalNumber *average = [afterDiscount decimalNumberByDividingBy:numProducts];
NSDecimalNumber *averageSquared = [average decimalNumberByRaisingToPower:2];
NSLog(@"Subtotal: %@", subtotal); // 45.98
NSLog(@"After coupon: %@", afterCoupon); // 40.98
NSLog((@"After discount: %@"), afterDiscount); // 36.882
NSLog(@"Average price per product: %@", average); // 18.441
NSLog(@"Average price squared: %@", averageSquared); // 340.070481
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