由于使用Double计算经常会在小数点后精度问题和上取整、下取整、四舍五入方面出现问题，所以决定使用十进制数做金额、利率的计算。 NSDecimalNumber是NSNumber的子类。
一、初始化
//实例方法
-(instancetype)initWithMantissa:(unsignedlonglong)mantissa exponent:(short)exponent isNegative:(BOOL)flag;
-(instancetype)initWithDecimal:(NSDecimal)dcm;
-(instancetype)initWithString:(nullableNSString *)numberValue;
-(instancetype)initWithString:(nullableNSString *)numberValue locale:(nullableid)locale;
//类方法
+(NSDecimalNumber *)decimalNumberWithMantissa:(unsignedlonglong)mantissa exponent:(short)exponent isNegative:(BOOL)flag;
+(NSDecimalNumber *)decimalNumberWithDecimal:(NSDecimal)dcm;+ (NSDecimalNumber *)decimalNumberWithString:(nullableNSString *)numberValue;
+(NSDecimalNumber *)decimalNumberWithString:(nullableNSString *)numberValue locale:(nullableid)locale;
**e.g. **
NSDecimalNumber *subtotalAmount = [[NSDecimalNumber alloc]initWithString: @"12.34"]; //12.34
subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1234 exponent:-2 isNegative:NO]; //12.34 (
mantissa：长整形；exponent：指数；flag：正负数)
subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1234 exponent:2 isNegative:YES]; //-123400
discountAmount = [NSDecimalNumber decimalNumberWithString:@"123.4"]; //123.4
//NSDecimal类型
C语言NSDecimal类型和十进制数转换
NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1234 exponent:-2 isNegative:NO]; //12.34
NSDecimal decimalValue = [subtotalAmount decimalValue];
subtotalAmount = [NSDecimalNumber decimalNumberWithDecimal:decimalValue]; //12.34
☐//字符串转换十进制数格式 : locale
locale代表一种格式，就像date的格式化一样。这里的locale可以传递两种格式
NSDictionary *locale = [NSDictionary dictionaryWithObject:@"," forKey:NSLocaleDecimalSeparator]; //以","当做小数点格式
NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4
NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"fr_FR"]; //法国数据格式,法国的小数点是','逗号
NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4
二、加减乘除
加法运算
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
减法运算
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
乘法运算
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
除法运算
- (NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
a的n次方
- (NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power;
- (NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
指数运算
- (NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power;
- (NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
四舍五入运算
- (NSDecimalNumber *)decimalNumberByRoundingAccordingToBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
比较运算
- (NSComparisonResult)compare:(NSNumber *)decimalNumber;
e.g.
NSDecimalNumber *discount1 = [NSDecimalNumber decimalNumberWithString:@"1.2"];
NSDecimalNumber *discount2 = [NSDecimalNumber decimalNumberWithString:@"1.3"];
NSComparisonResult result = [discount1 compare:discount2];
if (result == NSOrderedAscending) {
NSLog(@"discount1 < discount2");
} else if (result == NSOrderedSame) {
NSLog(@"discount1 == discount2");
} else if (result == NSOrderedDescending) {
NSLog(@"discount1 > discount2");
}
☐三、格式化处理
NSDecimalNumberHandler
- (instancetype)initWithRoundingMode(NSRoundingMode)roundingMode
scale:(short)scale
raiseOnExactness:(BOOL)exact
raiseOnOverflow:(BOOL)overflow
raiseOnUnderflow:(BOOL)underflow
raiseOnDivideByZero:(BOOL)divideByZero;
+ (NSDecimalNumberHandler *)defaultDecimalNumberHandler;
+ (instancetype)decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale raiseOnExactness:(BOOL)exact raiseOnOverflow:(BOOL)overflow raiseOnUnderflow:(BOOL)underflow raiseOnDivideByZero:(BOOL)divideByZero;
e.g.
NSDecimalNumberHandler *roundUp = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundBankers
scale:2
raiseOnExactness:NO
raiseOnOverflow:NO
raiseOnUnderflow:NO
raiseOnDivideByZero:YES];
NSDecimalNumber *subtotal = [NSDecimalNumberdecimalNumberWithString:@"11.4035"];
NSDecimalNumber *discount = [NSDecimalNumberdecimalNumberWithString:@"3.22"];
NSDecimalNumber *total = [subtotal decimalNumberByAdding:discount withBehavior:roundUp];//14.62 两个数相加然后舍去小数点后两位以后的部分
枚举
NSRoundPlain, // Round up on a tie // 貌似是四舍五入
NSRoundDown, // Always down == truncate // 只舍不入
NSRoundUp, // Always up // 只入不舍
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
End、未补充
☐NSDecimalNumberBehaviors
☐ NSDecimalNumberHandler
☐ NSRoundingMode
End、未验证
所有NSDecimalNumber是不可变的，这意味着已经被创建后不能改变它们的值。
