iOS 一次性解决关于金额输入问题

// OC版本

/// 用于控制金额输入
///
/// - Parameters:
///   - textField:
///   - range:
///   - string:
///   - decimalNumber: 小数点后几位
/// - Returns: bool值，建议直接在 textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Boo 调用
inline static bool isValidAboutInputTextField(UITextField *textfild, NSRange range, NSString * replacementString, NSInteger decimalNumber)  {
    NSScanner *scanner = [NSScanner scannerWithString:replacementString];
    NSCharacterSet *numbers;
    NSRange pointRange = [textfild.text rangeOfString:@"."];
    
    if (pointRange.location != NSNotFound && (pointRange.location > range.location + range.length || pointRange.location < range.location)) {
        numbers = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    } else {
        numbers = [NSCharacterSet characterSetWithCharactersInString:@"0123456789."];
    }
    
    if ([textfild.text isEqualToString:@""] && [replacementString isEqualToString:@"."]) { return false; }
    
    NSString *tempStr = [textfild.text stringByAppendingString:replacementString];
    if (pointRange.location != NSNotFound ) {
        if ([replacementString isEqualToString:@"."]) { return false; }
        if ( tempStr.length > 0 && (tempStr.length - pointRange.location) > decimalNumber + 1) { return false; }
    }
    
    NSRange zeroRange = [textfild.text rangeOfString:@"0"];
    if (zeroRange.location == 0 && zeroRange.length == 1) {
        if(pointRange.length == 0 && pointRange.location > 0){ 
            if([replacementString isEqualToString:@"0"]){
                return false;
            }
        }
    }
    
    NSString *buffer;
    if (![scanner scanCharactersFromSet:numbers intoString:&buffer] && replacementString.length) {
        return false;
    } else {
        return true;
    }
}

// Swift版本

/// 用于控制金额输入
///
/// - Parameters:
///   - textField:
///   - range:
///   - string:
///   - decimalNumber: 小数点后几位
/// - Returns: bool值，建议直接在 textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Boo 调用
func isValidAboutInputTextField(textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String, decimalNumber: Int) -> Bool {
     let scanner = Scanner.init(string: string)
     var numbers: CharacterSet
     let pointRange = textField.text!.toNSRange(textField.text!.range(of: "."))
        
     if ((pointRange?.location)! != NSNotFound && ((pointRange?.location)! > range.location + range.length) || (pointRange?.location)! < range.location) {
         numbers = CharacterSet.init(charactersIn: "0123456789")
     } else {
         numbers = CharacterSet.init(charactersIn: "0123456789.")
     }
        
     if textField.text == "" && string == "." { return false }
        
     let tempStr = textField.text! + string
     if pointRange?.location != NSNotFound {
         if string == "." { return false }
         if tempStr.count > 0 && (tempStr.count - (pointRange?.location)! > decimalNumber + 1) { return false }
     }
        
     let zeroRange = textField.text!.toNSRange((textField.text?.range(of: "0")))
     if zeroRange?.location == NSNotFound && zeroRange?.length == 1 {
         if (pointRange?.location)! > 0 && pointRange?.length == 0 {
             if string == "0" {
                 return false
             }
         }
     }
        
     var buffer = ""
     if !scanner.scanCharacters(from: numbers, into: AutoreleasingUnsafeMutablePointer(&buffer)) && string.count > 0 {
         return false
     } else {
         return true
     }
  }

其中swift因为Range 和 NSRange转换及其麻烦，并且swift的Range类型难以驾驭，特提供 String+Extensions进行拓展。和上面的方法搭配更加好用
func toNSRange(_ range: Range<String.Index>?) -> NSRange? {
     guard let from = range?.lowerBound.samePosition(in: utf16), let to = range?.upperBound.samePosition(in: utf16) else {
         return NSMakeRange(NSNotFound, 0)
     }
     return NSMakeRange(utf16.distance(from: utf16.startIndex, to: from), utf16.distance(from: from, to: to))
 }