UITextField控制键盘输入的字符（如只输入数字和大小写字母）

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
   
    NSCharacterSet *characterSet = [[NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFJHIGKLMNOPQRSTUVWXYZ1234567890"] invertedSet];
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:characterSet] componentsJoinedByString:@""];
    return [string isEqualToString:filtered];
   
}