輸入驗證碼或密碼，自動下一位 iOS

系統沒有textFeild 的相關當輸入內容改變時候的代理方法。。。所以我們自己加一個監聽來實現如下的效果

主要代碼如下：

[_code1F becomeFirstResponder];
    [_code1F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
    [_code2F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
    [_code3F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
    [_code4F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
    [_code5F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
    [_code6F addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];

-(void)textFieldDidChange :(UITextField *)textField{
    if (textField.text.length == 1) {
        if (textField == _code1F) {
            [_code2F becomeFirstResponder];
        }else if (textField == _code2F){
            [_code3F becomeFirstResponder];
        }else if (textField == _code3F){
            [_code4F becomeFirstResponder];
        }else if (textField == _code4F){
            [_code5F becomeFirstResponder];
        }else if (textField == _code5F){
            [_code6F becomeFirstResponder];
        }else{
            [self.view endEditing:YES];
        }
    }
}