InvalidOperationException 错误

Question

我正在创建一个方法来处理 DataList 中的删除按钮事件，并且它的功能正常，但是我得到了这个异常：

Collection was modified; enumeration operation may not execute.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.

这是我的代码：

protected void delete(object sender, CommandEventArgs e) 
        {
            if ((e.CommandName == "delete") && (e.CommandArgument != null))
            {
                foreach (DataListItem item in DataList2.Items)
                {
                    Label post_IDLabel = (Label)item.FindControl("post_IDLabel");
                    string connStr = ConfigurationManager.ConnectionStrings["MyDbConn"].ToString();
                    SqlConnection conn = new SqlConnection(connStr);
                    SqlCommand cmd = new SqlCommand("delete_post", conn);
                    cmd.CommandType = CommandType.StoredProcedure;
                    int post_ID = Convert.ToInt32(post_IDLabel.Text);
                    string email = Session["email"].ToString();
                    int course_ID = Convert.ToInt32(Request.QueryString["courseID"]);
                    cmd.Parameters.Add(new SqlParameter("@course_ID", course_ID));
                    cmd.Parameters.Add(new SqlParameter("@myemail", email));
                    cmd.Parameters.Add(new SqlParameter("@post_ID", post_ID));
                    conn.Open();
                    cmd.ExecuteNonQuery();
                    conn.Close();
                    DataList2.DataBind();
                }
            }

Answer 1

将DataList2.DataBind(); 排除在foreach 循环之外

            foreach (DataListItem item in DataList2.Items)
            {
                Label post_IDLabel = (Label)item.FindControl("post_IDLabel");
                string connStr = ConfigurationManager.ConnectionStrings["MyDbConn"].ToString();
                SqlConnection conn = new SqlConnection(connStr);
                SqlCommand cmd = new SqlCommand("delete_post", conn);
                cmd.CommandType = CommandType.StoredProcedure;
                int post_ID = Convert.ToInt32(post_IDLabel.Text);
                string email = Session["email"].ToString();
                int course_ID = Convert.ToInt32(Request.QueryString["courseID"]);
                cmd.Parameters.Add(new SqlParameter("@course_ID", course_ID));
                cmd.Parameters.Add(new SqlParameter("@myemail", email));
                cmd.Parameters.Add(new SqlParameter("@post_ID", post_ID));
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
            }
            DataList2.DataBind();

Answer 2

您在枚举时不能修改集合。 DataList2.DataBind修改DataList2.Items，这是不允许的。

如果您将DataBind 移到循环之外，它应该可以工作。

Answer 3

我想当您将 DataList2.DataBind 移出 foreach 时，您的问题就解决了。

但我认为你的代码有更多错误，你应该尽量避免从循环中调用数据库。您应该尝试重构此代码，以便只调用一次数据库。例如，在一个参数中传递所有帖子 ID。或者如果足够的话，也许只有 course_id 和 email。