本問引自于：
關(guān)于iOS數(shù)據(jù)解析小數(shù)丟失精度的問題AFNetworking

目前發(fā)現(xiàn)

//出現(xiàn)BUG的條件是兩位數(shù)或者一位數(shù)，且?guī)晌恍?shù)，類型還必須是float//兩位數(shù)：十位必須是7、8、9；個(gè)位數(shù)隨意，一位數(shù)的個(gè)位數(shù)也必須是789//兩位小數(shù)：第一位數(shù)隨意；第二位數(shù)必須是

下面是正常請(qǐng)求。

 NSURLSessionDataTask*task = [manager POST:httpStr parameters:secureDic progress:nilsuccess:^(NSURLSessionDataTask* _Nonnull task, id  _Nullable responseObject) {  
        //請(qǐng)求回來打印responseObject  
       if(!isRedirect) {  
           [selfsaveCookies];  
           requestBlock(responseObject,nil);  
       }  
        
    } failure:^(NSURLSessionDataTask* _Nullable task, NSError* _Nonnull error) {  
        if(![DataRequest haveInternet]) {  
               
            NSDictionary*mesDic = @{@"mes":DataRequestNoInternetMessage};  
            NSDictionary*notWorkDic = @{@"message":mesDic};  
            requestBlock(notWorkDic,nil);  
               
        }else  
            requestBlock(dic,nil);  
    }];

打印結(jié)果如下，discount字段，服務(wù)器返回的是double，9.70，AFNetworking解析后就成了9.699999999999

后來查了下，發(fā)現(xiàn)是蘋果的json解析會(huì)莫名其妙丟失精度

以下是測(cè)試結(jié)果

以下是測(cè)試結(jié)果   
NSString *jsonStr = @"{\"9.70\":9.70, \"97.40\":97.40, \"80.40\":80.40, \"188.40\":188.40}";
    NSLog(@"json:%@", jsonStr);
    NSData *jsonData_ = [jsonStr dataUsingEncoding:NSUTF8StringEncoding];
    NSError *jsonParsingError_ = nil;
    NSDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:[NSJSONSerialization JSONObjectWithData:jsonData_ options:0 error:&jsonParsingError_]];
    NSLog(@"dic:%@", dic);
    /*結(jié)果：dic:{
     "188.40" = "188.4";
     "80.40" = "80.40000000000001";
     "9.70" = "9.699999999999999";
     "97.40" = "97.40000000000001";
     }*/

解決辦法:

NSString *decimalNumberWithDouble(double conversionValue){  
    NSString *doubleString        = [NSString stringWithFormat:@"%lf", conversionValue];  
    NSDecimalNumber *decNumber    = [NSDecimalNumber decimalNumberWithString:doubleString];  
    return [decNumber stringValue];