Question

我在一个类中定义了这样的函数：

using System;
using System.Collections.Generic;

using System.Linq;
using System.Text;

using System.Data;
using System.Data.SqlClient;

using System.Windows.Forms;
using System.Configuration;
using System.Diagnostics;
using MFDBAnalyser;

namespace MFDBAnalyser

{

    public class DataAccessMaster:MFDBAnalyser

    {


        //        /// <summary>
        //        /// This function gets the list of all the databases present in the local server.
        //        /// </summary>
        //        /// <returns></returns>


        public static DataSet GetAllDataBaseNames()

        {

            SqlConnectionStringBuilder objConnectionString = new SqlConnectionStringBuilder();
            objConnectionString.DataSource = txtHost.Text;
            objConnectionString.UserID = txtUsername.Text;
            objConnectionString.Password = txtPassword.Text;

            SqlConnection sConnection = new SqlConnection(objConnectionString.ConnectionString);

            //If connected then give this message to user
            lblMessage.Visible = true;
            lblMessage.Text = "You are connected to the SQL Server....";

            try
            {
                //To Open the connection.
                sConnection.Open();

                //Query to select the list of databases.
                string selectDatabaseNames = @"SELECT 
                                                    NAME 
                                                 FROM 
                                                    [MASTER]..[SYSDATABASES]";

                //Create the command object
                SqlCommand sCommand = new SqlCommand(selectDatabaseNames, sConnection);

                //Create the data set 
                DataSet sDataset = new DataSet("master..sysdatabases");

                //Create the dataadapter object
                SqlDataAdapter sDataAdapter = new SqlDataAdapter(selectDatabaseNames, sConnection);
                sDataAdapter.TableMappings.Add("Table", "master..sysdatabases");

                //Fill the dataset
                sDataAdapter.Fill(sDataset);

                //Bind the database names in combobox
                DataViewManager dsv = sDataset.DefaultViewManager;

            }
            catch(Exception ex)
            {
                //All the exceptions are handled and written in the EventLog.
                EventLog logException = new EventLog("Application");
                logException.Source = "MFDBAnalyser";
                logException.WriteEntry(ex.Message);
                MessageBox.Show("Login Failed!!", "Error Occured");
            }
            finally
            {
                //If connection is not closed then close the connection
                if(sConnection.State != ConnectionState.Closed)
                {
                    sConnection.Close();
                }
            }
        }
    }
}

然后我在另一个类中调用了这个函数：

public void BindDBDropDown()

        {

 DataSet dsTablesWithoutForeignKeys = default(DataSet);

            try
            {
                //The function GetAllForeignKeyTables() is called from the class PluginManager.
                dsTablesWithoutForeignKeys = DataAccessMaster.GetAllDataBaseNames();

                cmbDatabases.DisplayMember = "TABLE_NAME";
                cmbDatabases.ValueMember = "";
                cmbDatabases.DataSource = dsTablesWithoutForeignKeys.Tables["master..sysdatabases"];
            }
            catch(Exception ex)
            {
                //All the exceptions are handled and written in the EventLog.
                EventLog logException = new EventLog("Application");
                logException.Source = "MFDBAnalyser";
                logException.WriteEntry(ex.Message);
            }
        }

但是显示错误，例如txtHost etx不存在，当我将designer.cs类的protected修饰符更改为public时，它也显示错误...

谁能告诉我发生了什么？

Answer 1

假设您的文本框是在MFDBAnayser类中定义的，您仍然无法在GetAllDataBaseNames函数中访问它们。 GetAllDataBaseNames是一个静态函数，因此它无法访问文本框或其他控件之类的实例变量。

Answer 2

验证txtHost的修饰符是否也受到保护或公开。

Answer 3

U无法获取另一个类中表单的值。尝试使用参数。或者使用properties {get ;set;}来获取值。我想你可以使用一些属性并分配文本框的值。如果你正在使用winforms，你可以使用静态变量。但是在web的情况下你必须传递参数。

控件不是从其他类继承的

3 个答案: