1、我們的app有一個判斷，當用戶輸入的值，小于等于剩余的余額時，給用戶彈窗，代碼不往下執(zhí)行
當用戶輸入 0.01 時，po 一下的結果是：0.10000.... ，當用戶的余額是0.01時，po一下網(wǎng)絡請求的返回結果是：0.009999...
當用戶輸入 66.05時，po 一下的結果是：66.049999...，當用戶的余額是66.05時，po一下網(wǎng)絡請求的返回結果是：66.049999...
所以，當數(shù)據(jù)較大時，不會有影響，因為用戶輸入的數(shù)據(jù)和網(wǎng)絡返回數(shù)據(jù)都被變成了不精確的小值了；但是，當數(shù)據(jù)較小時，用戶輸入的數(shù)據(jù)沒有被轉，網(wǎng)絡返回的數(shù)據(jù)被轉成了不精確的小值，導致用戶輸入永遠大于網(wǎng)絡返回的數(shù)據(jù)，代碼無法往下執(zhí)行；
解決：使用 NSDecimalNumber 將float、double數(shù)據(jù)轉化成NSDecimalNumber 類型的對象進行 +、-、*、/計算，再取值。
- (double)DecimalNumber:(double)num1 num2:(double)num2 { NSDecimalNumber *n1 = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%f",num1]]; NSDecimalNumber *n2 = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%f",num2]]; NSDecimalNumber *n3 = [n1 decimalNumberBySubtracting:n2]; return n3.doubleValue; } // 調(diào)用： double result = [self DecimalNumber: 2.01 num2: 2]; // 結果為 0.01 其中：
decimalNumberBySubtracting: n1 - n2，返回 n1 - n2 的結果值
decimalNumberByMultiplyingBy：n1 * n2，
decimalNumberByDividingBy：n1 / n2，
decimalNumberByAdding：n1 + n2，
compare：比較 n1 和 n2，返回比較結果；
2、進行數(shù)據(jù)的四舍五入獲得結果
- (NSString*)Rounding:(float)number afterPoint:(NSInteger)position { NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode: NSRoundPlain scale: position raiseOnExactness: NO raiseOnOverflow: NO raiseOnUnderflow:NO raiseOnDivideByZero: NO]; NSDecimalNumber *floatDecimal = [[NSDecimalNumber alloc] initWithFloat: number]; NSDecimalNumber *resultNumber = [floatDecimal decimalNumberByRoundingAccordingToBehavior:handler]; return [NSString stringWithFormat:@"%@",resultNumber]; } // 調(diào)用： NSString *result = [self Rounding:8.00092 afterPoint:3]; // 結果為 8.001 其中，參數(shù)number是需要四舍五入的數(shù)據(jù)，position是小數(shù)點后保留的位數(shù)；
高精度要求
使用系統(tǒng)提供的NSDecimalNumber API進行計算，最后轉換為字符串輸出顯示。NSDecimalNumber轉換方法：
#import "NSDecimalNumber+Y_Add.h"@implementation NSDecimalNumber (Y_Add)+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value{ return [self y_decimalNumberWithFloat:value scale:2];}+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value scale:(short)scale{ return [self y_decimalNumberWithFloat:value roundingMode:NSRoundBankers scale:scale];}+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value roundingMode:(NSRoundingMode)roundingMode scale:(short)scale{ return [[[NSDecimalNumber alloc] initWithFloat:value] y_decimalNumberHandlerWithRoundingMode:roundingMode scale:scale];}+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value{ return [self y_decimalNumberWithDouble:value scale:2];}+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value scale:(short)scale{ return [self y_decimalNumberWithDouble:value roundingMode:NSRoundBankers scale:scale];}+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value roundingMode:(NSRoundingMode)roundingMode scale:(short)scale{ return [[[NSDecimalNumber alloc] initWithFloat:value] y_decimalNumberHandlerWithRoundingMode:roundingMode scale:scale];} /** * <#Description#> * * @return <#return value description#> */- (NSDecimalNumber *)y_decimalNumberHandler{ return [self y_decimalNumberHandlerWithRoundingMode:NSRoundBankers scale:2];}- (NSDecimalNumber *)y_decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale{ NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:roundingMode scale:scale raiseOnExactness:NO raiseOnOverflow:YES raiseOnUnderflow:YES raiseOnDivideByZero:YES]; return [self decimalNumberByRoundingAccordingToBehavior:handler];}@end普通精度要求
使用系統(tǒng)提供的數(shù)學運算進行計算，最后轉換為字符串輸出顯示。保留小數(shù)點后N位的方法：
/** * formatterNumber .00 小數(shù)點后兩位 * * @param number <#number description#> * * @return <#return value description#> */+ (NSString *)y_formatterNumber:(NSNumber *)number{ return [self y_formatterNumber:number fractionDigits:2];}+ (NSString *)y_formatterNumber:(NSNumber *)number fractionDigits:(NSUInteger)fractionDigits{ NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init]; [numberFormatter setMaximumFractionDigits:fractionDigits]; [numberFormatter setMinimumFractionDigits:fractionDigits]; return [numberFormatter stringFromNumber:number];}以上就是本文的全部內(nèi)容，希望對大家的學習有所幫助，也希望大家多多支持武林網(wǎng)。
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