Question

我试图让我的头脑生成动态控件。我有一个Button1_Clickevent创建一个CheckBoxList（id = cblAnswers）或一个RadioButtonList（id = rblAnswers），具体取决于数据库中字段的值。

在Button3_Click事件上，我希望能够从生成的控件中检索所选值，并将它们与List listOfCorrectAnswerIDs进行比较。如果所选值与listOfCorrectAnswerIDs中的值完全匹配，我想设置变量。

我可以创建控件，但如何在Button3_Click中检索选定的值并将它们与List listOfCorrectAnswerIDs进行比较？

protected void Button1_Click(object sender, EventArgs e)
{
    string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
    MySqlConnection conn = new MySqlConnection(connStr);
    MySqlDataReader reader;

    List<string> listOfAnswerIDs = new List<string>();
    List<string> listOfAnswers = new List<string>();
    List<string> listOfCorrectAnswerIDs = new List<string>();

    try
    {
        conn.Open();
        string cmdText = "SELECT * FROM questions_m WHERE question_id=1";
        MySqlCommand cmd = new MySqlCommand(cmdText, conn);

        reader = cmd.ExecuteReader();

        if (reader.Read())
        {
            lblQuestion.Text = reader["question"].ToString();

            if (reader["type"].ToString().Equals("C"))
            {
                CheckBoxList cblAnswers = new CheckBoxList();
                cblAnswers.ID = "cblAnswers";
                Page.Form.Controls.Add(cblAnswers);
            }
            else if (reader["type"].ToString().Equals("R"))
            {
                 RadioButtonList rblAnswers = new RadioButtonList();
                 rblAnswers.ID = "rblAnswers";
                 Page.Form.Controls.Add(rblAnswers);
            }

            ViewState["QuestionID"] = reader["question_id"].ToString();
            reader.Close();

            string cmdText2 = "SELECT * FROM answers_m WHERE question_id=1";
            MySqlCommand cmdAnswers = new MySqlCommand(cmdText2, conn);
            reader = cmdAnswers.ExecuteReader();

            while (reader.Read())
            {
                listOfAnswerIDs.Add(reader["answer_id"].ToString());
                listOfAnswers.Add(reader["answer"].ToString());
                if (reader["correct"].ToString().Equals("Y"))
                {
                    listOfCorrectAnswerIDs.Add(reader["answer_id"].ToString());
                }
            }

            reader.Close();
            populateAnswers(listOfAnswers, listOfAnswerIDs);

        }
        else
        {
            reader.Close();
            lblError.Text = "(no questions found)";
        }
        ViewState["listOfCorrectAnswerIDs"] = listOfCorrectAnswerIDs;

    }
    catch
    {
        lblError.Text = "Database connection error - failed to read records.";
    }
    finally
    {
        conn.Close();
    }
}

    protected void Button3_Click(object sender, EventArgs e)
{
    if (((CheckBoxList)this.FindControl("cblAnswers")) != null)
    {
        List<string> selectedValues = ((CheckBoxList)this.FindControl("cblAnswers")).Items.Cast<ListItem>()
    .Where(li => li.Selected)
    .Select(li => li.Value)
    .ToList();
        for (int i = 0; i < selectedValues.Count; i++)
        {
            lblSelected.Text += selectedValues[i].ToString();
        }
    }
}

Answer 1

加载问题时，在ViewState中存储使用答案填充的控件的名称，并在按钮单击事件中检索控件名称并将其传递给FindControl（）。将结果转换为CheckBoxList和RadioButtonList的公共基类型，即ListControl。按钮处理程序可能如下所示：

protected void Button3_Click(object sender, EventArgs e)
{
    string controlName = ViewState["answerControlName"];
    ListControl answersControl = (ListControl)this.FindControl(controlName);
    if (answersControl != null)
    {
        List<string> selectedValues = answersControl.Items.Cast<ListItem>()
            .Where(li => li.Selected)
            .Select(li => li.Value)
            .ToList();

        List<string> listOfCorrectAnswerIDs = (List<string>)ViewState["listOfCorrectAnswerIDs"];

        // check for equivalency
        string selectedString = string.Join(",", selectedValues.OrderBy(val => val));
        string correctString = string.Join(",", listOfCorrectAnswerIDs.OrderBy(val => val));

        bool allAnswersCorrect = selectedString == correctString;
    }
}

您没有指定想要比较答案集，所以在这里我提供了一种简单的方法来检查这些集是否相同（对值进行排序，转换为逗号 - 分隔列表，并使用字符串相等）。如果你想要％校正，你最好循环找到正确的答案并检查每个答案，看它是否包含在selectedValues列表中，或者使用LINQ集操作函数如.Intersect()

Answer 2

这是因为您动态创建这些控件的方式。您在页面初始化了所有控件后创建它们，因此在每个PostBack上都会丢失它们。我建议您阅读ASP.NET Page Life Cycle。

您有几种方法可以实现目标。您可以覆盖CreateChildControls方法，也可以覆盖网页的OnInit方法。要么完成同样的事情，要记住如果使用后者，请调用基础Init方法。

protected override void CreateChildControls()
{
    CreateDynamicControls();
}

protected override void OnInit(EventArgs e)
{
    CreateDynamicControls();
    base.OnInit(e);
}

检索动态生成的控件的SelectedValues

2 个答案: