今天遇到了一个问题，本来json中返回的是Double类型，值为9.87，显示到Label 却是9.86999999999999

为了方便大家理解，我先做了如下演示

NSNumber *amount = [NSNumber numberWithDouble:9.87];
NSLog(@"normal amount %@", amount);

NSNumber *amount1 = [NSNumber numberWithDouble:3.87];   
NSLog(@"normal amount1 %@", amount1);

打印的值为
Test[8924:1150018] normal amount 9.869999999999999
Test[8924:1150018] normal amount1 3.87

有问题，就要开始解决，经过一番查找，找到了以下解决办法

//1
//该方法中会规定小数点的位数
NSString *amountString1 = [NSString stringWithFormat:@"%.2f",[amount doubleValue]];
NSLog(@"amountString1 %@",amountString1);

//2    
double amountDouble = [amount doubleValue];

NSString *amountDoubleStr = [NSString stringWithFormat:@"%lf", amountDouble];
NSDecimalNumber *amountNum = [NSDecimalNumber decimalNumberWithString:amountDoubleStr];

NSString *amountStr = [amountNum stringValue];
NSLog(@"amountStr %@", amountStr);

打印的值为
Test[9451:1317790] amountStr 9.87

//3
//该方法中会规定小数点的位数
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.maximumFractionDigits = 2;

NSString *amountString = [formatter stringFromNumber:amount];
NSLog(@"amountString %@",amountString);

打印的值为
Test[9451:1317790] amountString 9.87

//4
NSNumberFormatter *formatter2 = [[NSNumberFormatter alloc] init];
formatter2.numberStyle = NSNumberFormatterDecimalStyle;
//去掉千位分隔符，举例123,456.88加了这句会变成123456.88
[formatter2 setGroupingSeparator:@""]; 
 //formatter2.maximumFractionDigits 默认值是3

NSString *amountString2 = [formatter2 stringFromNumber:amount];
NSLog(@"amountString2 %@",amountString2);

打印的值为
Test[9451:1317790] amountString2 9.87

//建议添加category

//.h
@interface NSNumber (Cd)

- (NSString *)LGDoubleStringValue;

- (NSString *)LGDoubleStringValueWithDigits:(NSUInteger)digits;

@end

//.m
@implementation NSNumber (Cd)

- (NSString *)LGDoubleStringValue
{
    return [self LGDoubleStringValueWithDigits:2];
}

- (NSString *)LGDoubleStringValueWithDigits:(NSUInteger)digits
{
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    formatter.numberStyle = NSNumberFormatterDecimalStyle;
    formatter.maximumFractionDigits = digits;
    [formatter setGroupingSeparator:@""];
    
    NSString *retString = [formatter stringFromNumber:self];
    return retString;
}

@end

//使用方法

NSLog(@"%@",@(9.8712132123));
NSLog(@"%@",[@(9.87123131) LGDoubleStringValue]);
NSLog(@"%@",[@(9.871231313) LGDoubleStringValueWithDigits:5]);

//输出结果为
Test[10318:1500287] 9.871213212300001
Test[10318:1500287] 9.87
Test[10318:1500287] 9.87123

参考以下网址

出现问题的原因 https://www.aliyun.com/jiaocheng/400490.html
https://stackoverflow.com/questions/24246565/objective-c-double-to-nsstring-with-x-many-decimals
NSNumberFormatter属性