通常我们需要限制输入数字 字符 字母 或者中文等等
一般情况我们用到textfiled的代理方法去做

//
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

    NSCharacterSet *charer = [NSCharacterSet characterSetWithCharactersInString:@string">"12345"];
    NSString *filed  = [[string componentsSeparatedByCharactersInSet:charer] componentsJoinedByString:@string">""];
    if ([filed isEqualToString:string]) {
        return NO;
    }
    return yes;
}

这样就可以限制只输入 字符串里给出的字符

分享一个
限制只输入数字金额,并且限制输入最大数字,且自动判断输入0后变为小数点的方法

步骤.
设置textfiled的delegate = self;

//
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{


    return [ViewController moneyTextField:textField shouldChangeCharactersInRange:range replacementString:string max:1000];
}



#pragma mark - 限制输入数字以及最大值 方法实现
+(BOOL)moneyTextField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string max:(NSInteger)max
{
    //筛选输入内容确保正确性
    NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@string">"0123456789.\b"];
    string = [string stringByReplacingOccurrencesOfString:@string">" " withString:@string">""];
    if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {
        return NO;
    }

    BOOL isHasRadixPoint = YES;
    //小数点后面的位数
    NSInteger RadixPointNum = 2;
    NSString *existText = textField.text;
    //判断是否含有小数点
    if ([existText rangeOfString:@string">"."].location == NSNotFound) {
        isHasRadixPoint = NO;
    }

    if (string.length > 0) {
        unichar newChar = [string characterAtIndex:0];
        //开始进入判断文本
        if (existText.length>0) {
            if ([existText characterAtIndex:0]==string">'0') {
                //当首位是0的时候
                if (newChar==string">'0') {
                    //输入是零的时候判断是否有小数点
                    if (isHasRadixPoint) {
                        return range.location<=2;
                    }else{
                        return NO;
                    }
                }else if((newChar > string">'0' && newChar <= string">'9') &&existText.length<=1){
                    textField.text = @string">"";
                }
            }
        }

        if ((newChar >= string">'0' && newChar <= string">'9') || newChar == string">'.' ) {
            if (newChar == string">'.') {
                if (existText.length==0) {
                    textField.text = @string">"0.";
                    return NO;
                }else{
                    return !isHasRadixPoint;
                }
            }else {
                if (isHasRadixPoint) {
                    NSRange ran = [existText rangeOfString:@string">"."];
                    return (range.location - ran.location <= RadixPointNum);
                } else{
                    //小数点前面的位数
                    //return existText.length<6;
                    if ([textField.text isEqualToString:@string">"0"]){
                        textField.text = @string">"0.";
                    }
                    NSString *nowString;
                    if (range.length==0) {
                        nowString = [NSString stringWithFormat:@string">"%@%@",textField.text,string];
                    }else{
                        nowString = [textField.text stringByReplacingCharactersInRange:range withString:string];
                    }
                    //                    NSString *nowString = [textField.text stringByReplacingCharactersInRange:range withString:string];
                    if (nowString.doubleValue>= max) {
                        textField.text = [NSString stringWithFormat:@string">"%ld",max];
                        return NO;
                    }
                    return nowString.doubleValue <= max;
                }
            }
        }else {
            return YES;
        }
    }
    return YES;
}