UITextField只能输入数字NSCharacterSet实现

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSCharacterSet *charSet = [[NSCharacterSet characterSetWithCharactersInString:@"0123456789"] invertedSet];
    NSString *filteredStr = [[string componentsSeparatedByCharactersInSet:charSet] componentsJoinedByString:@""];
    if ([string isEqualToString:filteredStr]) {
        return YES;
    }
    return NO;
}