ios开发中涉及到和货币价格计算相关的，都需要注意计算精度的问题。
服务器有可能返回的金钱是int float double string NSNumber, 单纯的float、double的计算都会出现精度问题，即使只是两位小数，也会出现误差。
苹果为我们提供了NSDecimalNumber的API来处理金钱的计算的问题：
1、字符串转float等不精确问题。
2、精确计算
3、保留小数位数
4、四舍五入及其它的保留小数位数规则
NSDecimalNumber的使用
**1.把相应的类型转换成NSDecimalNumber类型 **
//1、NSString -> NSDecimalNumber
NSDecimalNumber *num1 = [NSDecimalNumber decimalNumberWithString:@"100"];
NSLog(@"%@",num1);
//2、NSNumber -> NSDecimalNumber(基础类型的话，先转成NSNumber)
NSDecimalNumber *num2 = [NSDecimalNumber decimalNumberWithDecimal:[[NSNumber numberWithInt:50] decimalValue]];
NSLog(@"%@",num2);
2.相关运算
加+
/*加 +
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id )behavior;//带保留小数位数
*/
NSDecimalNumber *num3 = [num1 decimalNumberByAdding:num2];
NSLog(@"num3 == %@",num3);
减 -
/*减 -
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id )behavior;//带保留小数位数
*/
NSDecimalNumber *num4 = [num1 decimalNumberBySubtracting:num2];
NSLog(@"num4 == %@",num4);
乘 *
/*乘 *
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id )behavior;//带保留小数位数
*/
NSDecimalNumber *num5 = [num1 decimalNumberByMultiplyingBy:num2];
NSLog(@"num5 == %@",num5);
除 \
/*除 \
- (NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id )behavior;//带保留小数位数
*/
NSDecimalNumber *num6 = [num1 decimalNumberByDividingBy:num2];
NSLog(@"num6 == %@",num6);
比较
/*比较
- (NSComparisonResult)compare:(NSNumber *)decimalNumber;
*/
NSComparisonResult result = [num1 compare:num2];
NSLog(@"result == %ld",(long)result);
保留小数及相关参数含义
// 保留小数
+ (instancetype)decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale raiseOnExactness:(BOOL)exact raiseOnOverflow:(BOOL)overflow raiseOnUnderflow:(BOOL)underflow raiseOnDivideByZero:(BOOL)divideByZero;
//1、 NSRoundingMode
// 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
// Down 1.2 1.2 1.2 1.3 1.2
// Up 1.2 1.3 1.3 1.4 1.3
// Bankers 1.2 1.2 1.2 1.4 1.3
/* typedef NS_ENUM(NSUInteger, NSRoundingMode) {
NSRoundPlain, // Round up on a tie 四舍五入
NSRoundDown, // Always down == truncate 向下保留
NSRoundUp, // Always up 向上保留
NSRoundBankers // on a tie round so last digit is even 貌似是：
if(四舍五入位 == 5)（四舍五入位（5）+ 保留位 ）%2 == 0 ？ 入 ： 舍 ；
if(四舍五入位 ！= 5) 遵从四舍五入
};
*/
//2、scale 保留小数个数
//3、其它：溢出等是否报错
NSDecimalNumber *num_1 = [NSDecimalNumber decimalNumberWithString:@"1.2"];
NSDecimalNumber *num_2 = [NSDecimalNumber decimalNumberWithString:@"3.1415926"];
NSDecimalNumberHandler *handel = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundBankers scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
NSDecimalNumber *num_3 = [num_1 decimalNumberByMultiplyingBy:num_2 withBehavior:handel];
NSLog(@"num_3 == %@",num_3);
3.对金钱进行千分位和保留两位小数处理
3.1使用NSNumberFormatter去格式化
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.numberStyle = kCFNumberFormatterCurrencyAccountingStyle;
NSString *newAmount = [formatter stringFromNumber:[NSNumber numberWithLong:[@"10000" integerValue]]];
NSLog(@"newAmount==%@",newAmount);
/*
typedef CF_ENUM(CFIndex, CFNumberFormatterStyle) { // number format styles
kCFNumberFormatterNoStyle = 0,
kCFNumberFormatterDecimalStyle = 1,
kCFNumberFormatterCurrencyStyle = 2,
kCFNumberFormatterPercentStyle = 3,
kCFNumberFormatterScientificStyle = 4,
kCFNumberFormatterSpellOutStyle = 5,
kCFNumberFormatterOrdinalStyle CF_ENUM_AVAILABLE(10_11, 9_0) = 6,
kCFNumberFormatterCurrencyISOCodeStyle CF_ENUM_AVAILABLE(10_11, 9_0) = 8,
kCFNumberFormatterCurrencyPluralStyle CF_ENUM_AVAILABLE(10_11, 9_0) = 9,
kCFNumberFormatterCurrencyAccountingStyle CF_ENUM_AVAILABLE(10_11, 9_0) = 10,
};
*/
3.2 - 工作中常用的工具
/// 处理json float double 精度丢失问题
- (NSString *)ym_decimalNumber {
NSString *doubleString = [NSString stringWithFormat:@"%f", self.doubleValue];
NSDecimalNumber *decNumber = [NSDecimalNumber decimalNumberWithString:doubleString];
return [decNumber stringValue];
}
/// 金钱显示 100,000.00
+ (NSString *)ym_formatDecimalNumber:(NSString *)string {
if (!string || string.length == 0) {
return string;
}
NSNumber *number = @([string doubleValue]);
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.numberStyle = kCFNumberFormatterDecimalStyle;
formatter.positiveFormat = @"###,##0.00";
NSString *amountString = [formatter stringFromNumber:number];
return amountString;
}
/**
金钱显示 0.00 小数点后2位 & 符号 变小
*/
+ (NSAttributedString *)ym_priceString:(NSString *)text textColor:(UIColor *)textColor smallFont:(UIFont *)smallFont bigFont:(UIFont *)bigFont symbol:(NSString *)symbol
{
if (!text || text.length == 0) {
text = @"0.00";
}
NSRange range = [text rangeOfString:@"."];
if (range.length == 0) {
return [[NSAttributedString alloc] initWithString:@""];
}
NSArray *texts = [text componentsSeparatedByString:@"."];
NSMutableAttributedString *mStr = [[NSMutableAttributedString alloc]initWithString:symbol.length ? symbol : @"" attributes:@{NSFontAttributeName:smallFont,NSForegroundColorAttributeName:textColor}];
NSAttributedString *bigStr = [[NSAttributedString alloc]initWithString:texts[0] attributes:@{NSFontAttributeName:bigFont,NSForegroundColorAttributeName:textColor}];
NSAttributedString *pointStr = [[NSAttributedString alloc]initWithString:@"." attributes:@{NSFontAttributeName:smallFont,NSForegroundColorAttributeName:textColor}];
NSAttributedString *smallStr = [[NSAttributedString alloc]initWithString:texts[1] attributes:@{NSFontAttributeName:smallFont,NSForegroundColorAttributeName:textColor}];
[mStr appendAttributedString:bigStr];
[mStr appendAttributedString:pointStr];
[mStr appendAttributedString:smallStr];
return mStr;
}
/**
* 中划线
*/
+ (NSAttributedString *)ym_strikethroughString:(NSString *)text textColor:(UIColor *)textColor font:(UIFont *)font symbol:(NSString *)symbol
{
if (!text || text.length == 0) {
return [[NSAttributedString alloc] initWithString:@""];
}
NSDictionary *dic = @{NSFontAttributeName:font,NSForegroundColorAttributeName:textColor,NSStrikethroughStyleAttributeName: [NSNumber numberWithInt:NSUnderlineStyleSingle]};
NSAttributedString *astr = [[NSAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@%@", symbol,text] attributes:dic];
return astr;
}