我可以限制UITextField的字符集吗?

您可以尝试使用以下UITextFieldDelegate方法:

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

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    // Only characters in the NSCharacterSet you choose will insertable.
    NSCharacterSet *invalidCharSet = [[NSCharacterSet characterSetWithCharactersInString:@"abcdefgABCDEFG"] invertedSet];
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:invalidCharSet] componentsJoinedByString:@""];
    return [string isEqualToString:filtered];
}

尝试使用 UIKeyboardTypeNamePhonePad UITextField . 上面只有字母和数字:

textField.keyboardType = UIKeyboardTypeNamePhonePad;

使用Interface builder,您可以链接并获取任何函数中“编辑已更改”的事件。现在你可以检查长度了

- (IBAction)onValueChange:(id)sender 
{
    NSString *text = nil;
    int MAX_LENGTH = 20;
    switch ([sender tag] ) 
    {
        case 1: 
        {
            text = myEditField.text;
            if (MAX_LENGTH < [text length]) {
                myEditField.text = [text substringToIndex:MAX_LENGTH];
            }
        }
            break;
        default:
            break;
    }

}