c# - asp.net 错误：无法将类型“对象”隐式转换为“字符串”。存在显式转换（您是否缺少演员表？）

Question

我想使用 select WHERE 语句从名为 hotel 的 sql server 表中检索数据，但出现上述错误。任何人都可以帮忙吗？

SqlConnection cnn = new
        SqlConnection(ConfigurationManager.ConnectionStrings["myConnectionString"].ToString());
cnn.Open();
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "SELECT RoomsAvailable FROM Hotel WHERE HotelName = '" + 
                    this.DropDownList1.Text + "'";
cmd.Connection = cnn;
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
DataSet ds = new DataSet();
da.Fill(ds, "Hotel");
SqlCommandBuilder cb = new SqlCommandBuilder(da);
DataRow dsRow = null;
foreach (DataRow dsRow_loopVariable in ds.Tables["Hotel"].Rows)
{
    dsRow = dsRow_loopVariable;
    //This line is where the error comes in.
    this.txtHotel.Text = (dsRow["RoomsAvailable"]);
}

Answer 1

改变

this.txtHotel.Text = (dsRow["RoomsAvailable"]);

至

this.txtHotel.Text = (dsRow["RoomsAvailable"].ToString());

Answer 2

或更改为

this.txtHotel.Text = dsRow["RoomsAvailable"] as string;

如果值为空，您将不会得到异常。

Answer 3

试试这个代码

 this.txtHotel.Text = Convert.ToString (dsRow["RoomsAvailable"]);

Answer 4

dsRow["RoomsAvailable"]是一个类型的对象DataRow，如果你想要String值你需要调用ToString()：

this.txtHotel.Text = (dsRow["RoomsAvailable"].ToString());

文档

Answer 5

好吧，我看到了这段代码

cmd.CommandText = "SELECT RoomsAvailable FROM Hotel WHERE HotelName = '" + 
                    this.DropDownList1.Text + "'";

并将this.DropDownList1.Text获取您选择的值而不是 text 。只是你给出HotelNames了dropdown价值观吗？

并为错误尝试

Convert.ToString(dsRow ["RoomsAvailable"]);