- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    NSMutableString * futureString = [NSMutableString stringWithString:textField.text];
    [futureString  insertString:string atIndex:range.location];
    NSInteger flag=0;
    const NSInteger limited = 2;//小数点后需要限制的个数
    for (int i = (int)(futureString.length - 1); i>=0; i--) {
        if ([futureString characterAtIndex:i] == '.') {
            if (flag > limited) {
                return NO;
            }
            break;
        }
        flag++;
    }
    return YES;
}