參考文檔

常用NSDateFormatter，但少見NSNumberFormatter ，但后者似乎功能更豐富，也更實用。

類方法

/*
     eg. 12345.345
     NSNumberFormatterNoStyle //四舍五入整數
     NSNumberFormatterDecimalStyle //小數形式
     NSNumberFormatterCurrencyStyle //本地貨幣樣式，保留兩位小數 $12,345.34
     NSNumberFormatterPercentStyle   //百分比樣式  1,234,534%
     NSNumberFormatterScientificStyle  //科學計數樣式  1.2345345E4
     NSNumberFormatterSpellOutStyle //朗讀樣式 twelve thousand three hundred forty-five point three four five
     
     iOS 9.0后
     NSNumberFormatterOrdinalStyle            //序數樣式  12,345th
     NSNumberFormatterCurrencyISOCodeStyle   //貨幣代碼樣式  USD12,345.34
     NSNumberFormatterCurrencyPluralStyle    //本地貨幣樣式  12,345.34 US dollars
     NSNumberFormatterCurrencyAccountingStyle //會計計數  $12,345.34
     */
    NSNumber *number = [NSNumber numberWithDouble:12345.345];
    NSString *numberNoStyleStr = [NSNumberFormatter localizedStringFromNumber:number numberStyle:NSNumberFormatterCurrencyAccountingStyle];

實例方法

    //實例方法
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc]init];
    //舍入值
    formatter.roundingIncrement = @10;
    formatter.roundingMode = kCFNumberFormatterRoundUp;
    NSLog(@"%@",[formatter numberFromString:@""]);

    //樣式
    formatter.numberStyle = NSNumberFormatterDecimalStyle ;
    //寬度，包括前后綴在內的寬度
    formatter.formatWidth = 12;
    //填充位置符（單個字符）
    formatter.paddingCharacter = @"X";
    formatter.paddingPosition = NSNumberFormatterDecimalStyle;
    /*
     NSNumberFormatterPadBeforePrefix
     NSNumberFormatterPadAfterPrefix
     NSNumberFormatterPadBeforeSuffix
     NSNumberFormatterPadAfterSuffix
     */

    //后綴
    formatter.positiveSuffix = @"元";
    //前綴
    formatter.positivePrefix = @"￥";
    //縮放因子
    formatter.multiplier = @10;
    //負數樣式
    formatter.negativeFormat = @"-";
    //正數樣式
    formatter.positiveFormat = @"+";
    //小數點的樣式
    formatter.decimalSeparator = @".";
    //零的樣式
    formatter.zeroSymbol = @"0";
    
    //設置了這個后，會自動用0補充而不用位置符
    //整數的最多/少位數
    formatter.maximumIntegerDigits = 100;
    formatter.minimumIntegerDigits = 10;
    //小數的最多/少位數
    formatter.maximumFractionDigits = 10;
    formatter.minimumFractionDigits = 7;

    NSLog(@"%@",[formatter stringFromNumber:number]);