由于使用Double計算經常會在小數點后精度問題和上取整、下取整、四舍五入方面出現問題，所以決定使用十進制數做金額、利率的計算。 NSDecimalNumber是NSNumber的子類。
一、初始化
//實例方法
-(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;
//類方法
+(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：長整形；exponent：指數；flag：正負數)
subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1234 exponent:2 isNegative:YES]; //-123400
discountAmount = [NSDecimalNumber decimalNumberWithString:@"123.4"]; //123.4
//NSDecimal類型
C語言NSDecimal類型和十進制數轉換
NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1234 exponent:-2 isNegative:NO]; //12.34
NSDecimal decimalValue = [subtotalAmount decimalValue];
subtotalAmount = [NSDecimalNumber decimalNumberWithDecimal:decimalValue]; //12.34
?//字符串轉換十進制數格式 : locale
locale代表一種格式，就像date的格式化一樣。這里的locale可以傳遞兩種格式
NSDictionary *locale = [NSDictionary dictionaryWithObject:@"," forKey:NSLocaleDecimalSeparator]; //以","當做小數點格式
NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4
NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"fr_FR"]; //法國數據格式,法國的小數點是','逗號
NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4
二、加減乘除
加法運算
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
減法運算
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
乘法運算
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
除法運算
- (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;
指數運算
- (NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power;
- (NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power withBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
四舍五入運算
- (NSDecimalNumber *)decimalNumberByRoundingAccordingToBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;
比較運算
- (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、格式化處理
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 兩個數相加然后舍去小數點后兩位以后的部分
枚舉
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) 遵從四舍五入
End、未補充
?NSDecimalNumberBehaviors
? NSDecimalNumberHandler
? NSRoundingMode
End、未驗證
所有NSDecimalNumber是不可變的，這意味著已經被創建后不能改變它們的值。
