获取data（）编译错误 [英] Get data() compilation error

问题描述

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Text;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DropDownList1.DataSource = GetData();
            DropDownList1.DataValueField = "Branch";
            DropDownList1.DataTextField = "Branch";
            DropDownList1.DataBind();
        }
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        using (SqlConnection Cn = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=F:\AAAAAAAAAAA\FINGERPRINT\APP_DATA\QUESTIONS.MDF;Integrated Security=True;")) 
        {
            using (SqlCommand Cmd = new SqlCommand("select * from questions where Branch= @Branch"))
            {
                Cn.Open();

                Cmd.Parameters.AddWithValue("@Branch", int.Parse(DropDownList1.SelectedValue));
                SqlDataReader Dr = Cmd.ExecuteReader();
                if (Dr.HasRows)
                {
                    GridView1.DataSource = Dr;
                    GridView1.DataBind();
                }
                Dr.Close();

                Cn.Close();
            }

        }
    }
   DataTable GetData()
    {
        DataTable dt = new DataTable();
         SqlConnection Con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=F:\AAAAAAAAAAA\FINGERPRINT\APP_DATA\QUESTIONS.MDF;Integrated Security=True;");
        {
             SqlCommand Cmd = new SqlCommand("SELECT * FROM  questions ");
            
                Con.Open();
                SqlDataAdapter adpt = new SqlDataAdapter(Cmd);
                adpt.Fill(dt);
            }

        }
    }

我尝试过：



i尝试添加受保护但在数据表中得到相同的错误getdata（）

What I have tried:

i have try add protected but get same error in data table getdata()

推荐答案

在GetData（）方法中，您正在创建数据表但从不返回它，因此我假设您的编译错误是并非所有路径都返回值。它应该如下所示：

In GetData() method you are creating the data table but never returning it so I assume your compilation error is "not all paths are returning a value". It should look like this:

DataTable GetData()
{
    DataTable dt = new DataTable();
    using(SqlConnection Con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=F:\AAAAAAAAAAA\FINGERPRINT\APP_DATA\QUESTIONS.MDF;Integrated Security=True;"))
    using(SqlCommand Cmd = new SqlCommand("SELECT * FROM  questions ", Con))
    {		
    	Con.Open();
    	SqlDataAdapter adpt = new SqlDataAdapter(Cmd);
    	adpt.Fill(dt);
    }
    return dt; // <-- this is what you were missing
}

请注意我添加了使用语句，因为SqlConnectin和SqlCommand都实现了IDisposable。

Please note I added using statements as both SqlConnectin and SqlCommand implement IDisposable.

您将GetData声明为返回DataTable，但该方法不返回任何内容。

在方法结尾处添加以下行：

You declared GetData as returning a DataTable, but the method does not return anything.
Add this line at the end of the method:

return dt;

BTW：不要对连接字符串进行硬编码：从配置文件中读取它们！

BTW: don't hardcode connection strings: read them from a configuration file!

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