設(shè)置 delegate

1. 輸入長度限制：

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    
    if (textField == self.liveThemeTextField) {
    //這里的if時候為了獲取刪除操作,如果沒有次if會造成當達到字數(shù)限制后刪除鍵也不能使用的后果.
        if (range.length == 1 && string.length == 0) {
            return YES;
        }
        //so easy
        else if (self.liveThemeTextField.text.length >= 30) {
            self.liveThemeTextField.text = [textField.text substringToIndex:30];
            return NO;
        }
    }
    return YES;
}

2. 限制輸入空格：

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

{
    NSString *tem = [[string componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]componentsJoinedByString:@""];

    if (![string isEqualToString:tem]) {
        return NO;
    }
    return YES;
}