请问我这些错误 [英] hellp me please with these error

问题描述

错误是这样的：ExecuteReader需要一个开放且可用的连接。连接当前状态已关闭。

这些是类

error is this: ExecuteReader requires an open and available Connection. The connections current state is closed.
these are classes

namespace TestingApplication.Classes
{
    class DbBroker
    {
        static string CS = @"data source=C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA;database=testing_app;integrated security=true";
        public SqlConnection conn;
        public static DbBroker dbInstance;

        public static DbBroker GetBroker()
        {
            if (dbInstance == null)
            {
                dbInstance = new DbBroker();
                dbInstance.Open();
            }
            return dbInstance;
        }

        public SqlConnection Conn()
        {
            return new SqlConnection(CS);
        }
        public SqlConnection Open()
        {
            conn = Conn();
            conn.Open();
            return conn;
        }
        public void Close()
        {
            conn.Close();
        }
        public string[] GetRow(string query)
        {
            SqlCommand cmd = new SqlCommand(query, conn);
            SqlDataReader rdr = cmd.ExecuteReader();
            string[] res = new string[rdr.FieldCount];
            rdr.Read();
            for (int i = 0; i < rdr.FieldCount; i++)
                res[i] = rdr[i].ToString();
            rdr.Close();
            return res;
        }
        public List<string[]> GetRows(string query)
        {
            SqlCommand cmd = new SqlCommand(query, conn);
            SqlDataReader rdr = cmd.ExecuteReader();
            string[] row;
            List<string[]> res = new List<string[]>();
            while (rdr.Read())
            {
                row = new string[rdr.FieldCount];
                for (int i = 0; i < rdr.FieldCount; i++)
                    row[i] = rdr[i].ToString();
                res.Add(row);
            }
            rdr.Close();
            return res;
        }
        public string GetString(string query)
        {
            SqlCommand cmd = new SqlCommand(query, conn);
            SqlDataReader rdr = cmd.ExecuteReader();
            string res;
            rdr.Read();
            res = rdr[0].ToString();
            rdr.Close();
            return res;
        }
    }
}

namespace TestingApplication
{
    /// <summary>
    /// Interaction logic for Test.xaml
    /// </summary>
    public partial class Test : UserControl
    {
        int TestId = 1;
        public Test()
        {
            InitializeComponent();
            Classes.TestClass test = Classes.TestClass.GetById(TestId);
            Dictionary<int, Classes.Question>.Enumerator en = test.questions.GetEnumerator();
            en.MoveNext();
            lblQuestion.Content = en.Current.Value.text;
            foreach(Classes.Answer an in en.Current.Value.answers)
            {
                RadioButton rb = new RadioButton();
                rb.Content = an.text;
                rb.FontSize = 12;
                rb.Margin = new Thickness(0, 0, 0, 5);
                stackPanel1.Children.Add(rb);
            }
            btnBack.Visibility = Visibility.Hidden;
        }
    }
}

class TestClass
{
    public Dictionary<int, Question> questions;
    public int id;
    public string title;
    public string description;
    public DateTime creationdate;
    public static TestClass GetById(int id)
    {
        DbBroker db = DbBroker.GetBroker();
        string[] testRow = db.GetRow("select * from tests where id = " + id);
        TestClass t = new TestClass();
        t.title = testRow[1];
        t.questions = new Dictionary<int, Question>();
        List<string[]> questionsList = db.GetRows("select questions.id, questions.question,answers.id,answers.answer,answers.question,answers.points from questions join questions_tests on questions_tests.question = questions.id join answers on questions.id = answers.question where questions_tests.test = " + id);
        Question q;
        foreach (string[] q_string_arr in questionsList)
        {
            int qid = int.Parse(q_string_arr[0]);
            if (!t.questions.ContainsKey(qid))
            {
                q = new Question();
                q.text = q_string_arr[1];
                t.questions.Add(qid, q);
                t.questions[qid].answers = new List<Answer>();
            }
            Answer a = new Answer();
            a.id = int.Parse(q_string_arr[2]);
            a.text = q_string_arr[3];
            a.points = int.Parse(q_string_arr[4]);
            a.correct = (a.points > 0) ? true : false;
            t.questions[qid].answers.Add(a);
        }
        return t;
    }
}

<d:DesignHeight="367" d:DesignWidth="572">
    <Grid>
        <Label FontSize="12" Content="1. Some question" Height="42" HorizontalAlignment="Left" Margin="12,12,0,0" Name="lblQuestion" VerticalAlignment="Top" Width="239" />
        <Line Stroke="#bcb4b2" StrokeThickness="2" X1="0" Margin="0,56,0,0" VerticalAlignment="Top" Stretch="Fill" X2="1" Y1="50" Y2="50" />
        <StackPanel Height="250" HorizontalAlignment="Left" Margin="12,65,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="548"/>
        <Button Content="Next" Height="34" Margin="471,321,12,0" Name="btnNext" VerticalAlignment="Top" />
        <Button Content="Back" Height="34" HorizontalAlignment="Left" Margin="12,321,0,0" Name="btnBack" VerticalAlignment="Top" Width="89" />
    </Grid>
</UserControl>

推荐答案

你有一个类级别 conn 变量，它作为SQL命令的一部分使用：

You have a class level conn variable, which you use as part of the SQL command:

SqlCommand cmd = new SqlCommand(query, conn);

但是......你永远不会打电话给你的Open方法给它一个值，或者打开连接...



我自己也不会这样做：我使用块在中直接创建并打开SqlConnection，这样就会关闭并自动处理。我也会对SqlCommand对象做同样的事情！

But...you never call your Open method to give it a value, or open the connection...

And I wouldn't do it like that myself: I'd create and open the SqlConnection directly within a using block so that is gets Closed and Disposed automatically. And I'd do the same with the SqlCommand objects as well!

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