如何让textField的输入框只能输入特定字符

实现代理方法:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string   // return NO to not change text

{

    NSCharacterSet *cs;
    cs = [[NSCharacterSet characterSetWithCharactersInString:@"123"]invertedSet];

    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs]componentsJoinedByString:@""]; //按cs分离出数组,数组按@""分离出字符串
    BOOL canChange = [string isEqualToString:filtered];

    if (![string isEqualToString:@""]) {
        if ([filtered isEqualToString:@""]) {

            //弹出一个提示，提示只能输入123，不能输入以外的字符

        }
    }

    return canChange;

}