使用C#检查文本是否已退出SQL Server

Question

我第一次使用C#和SQL Server构建简单的ERP系统。我试图检查textBox中的值是否已经存在于数据库中；当窗体打开并键入字段时，我得到一个异常

下面是检查函数：

    private void txtRef_Validated(object sender, EventArgs e)
    {          
        BL.CLS_PRODUCTS prd = new BL.CLS_PRODUCTS();
        DataTable Dt = new DataTable();
        Dt = prd.VarifyProductID(txtRef.Text);

        if (Dt.Rows.Count > 0)
        {
            MetroMessageBox.Show(this, "الصنف موجود مسبقاً", "تنبيه", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            txtRef.Focus();
            txtRef.SelectionStart = 0;
            txtRef.SelectionLength = txtRef.Text.Length;
        }
    }

da.Fill(dt);

public DataTable SelectData(string stored_procedure, SqlParameter[] param)
{
        SqlCommand sqlcmd = new SqlCommand();
        sqlcmd.CommandType = CommandType.StoredProcedure;
        sqlcmd.CommandText = stored_procedure;
        sqlcmd.Connection = sqlconnection;

        if (param != null)
        {
            for (int i = 0; i < param.Length; i++)
            {
                sqlcmd.Parameters.Add(param[i]);
            }
        }

        SqlDataAdapter da = new SqlDataAdapter(sqlcmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        return dt;
    }

public DataTable VerifyProductID(string ID)
{
    DAL.DataAccessLayer DAL = new DAL.DataAccessLayer();
    DataTable Dt = new DataTable();

    SqlParameter[] param = new SqlParameter[1];
    param[0] = new SqlParameter("@ID", SqlDbType.VarChar, 50);
    param[0].Value = ID;

    Dt = DAL.SelectData("VerifyProductID", null);
    DAL.Close();

    return Dt;
}

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER PROC [dbo].[VerifyProductID]
    @ID VARCHAR(50)
AS
    SELECT * 
    FROM PRODUCTS 
    WHERE ID = @ID

StackTrace:
位于System.data.sqlclient.sqlConnection.onerror（SqlException exception,Boolean breakConnection,Action1 wrapCloseInAction）位于System.data.sqlClient.sqlInternalConnection.onerror（SqlException exception,Boolean breakConnection,Action1 wrapCloseInAction）位于System.data.sqlClient.tdSparser.throwException在System.data.sqlclient.SqlDataReader.tryconsumemetadata（）在System.data.sqlclient.SqlCommand.finishexecuteReader（sqldataader ds,RunBehavior RunBehavior,String rehtml" target="_blank">setOptionsString）在system.data.sqlclient.SqlCommand.runExecuteReadds（CommandBehavior cmdBehavior,RunBehavior RunBehavior,Boolean returnSsystem.data.sqlclient.sqlcommand.runexecuteReader（CommandBehavior cmdBehavior,RunBehavior RunBehavior,Boolean returnStream,String method,task&task,Boolean asyncWrite,String method,TaskCompletionSource`1 Complinition,Int32 timeout,Int32 timeout,task&task,Boolean asyncWrite）D.ExecuteDbDataReader（CommandBehavior behavior）在System.data.common.dbCommand.System.data.common.dbCommand.IDbCommand.ExecuteReader（CommandBehavior behavior）在System.data.common.dbDataAdapter.Fillinternal（DataSet DataSet,DataTable[]datatables,Int32 startRecord,Int32 maxRecords,String srcTable,IDbCommand command,CommandBehavior,Int32 maxRecords,IDbCommand命令,CommandBehavior）在System.data.common.dbdataAdapter.fill（DataTable DataTable）在e_and_m.dal.dataAccesslayer.selectData(String stored_procedure,sqlparameter[]param)在C:\users\kh\documents\visual Studio 2012\projects\e_and_m\e_and_m\dal\disual Studio 2012\drojects\dataAccesslayer.cs:c中的add_proudect.txtref_validated（对象发件人，EventArgs e）在C:\users\kh\documents\visual Studio 2012\projects\e_and_m\e_and_m\pl\frm_add_proudect.cs:第33行在system.windows.forms.Control.onvalidated（EventArgs e）在system.windows.forms.Control.performcontrolidated（Boolean bulkValidation）在

Answer 1

Dt = DAL.SelectData("VarifyProductID", null);

应该是

Dt = DAL.SelectData("VarifyProductID", param);