如何从c＃中的List 获取bool值？

hi i am converting a vb project into c# from a youtube tutorial by mkaatr he use a variable

嗨,我正在通过mkaatr从youtube教程将vb项目转换为c#,他使用了一个变量

 Private DBMSResultSets As List(Of Object)

so i use a variable in c# private List<object> DBMSResultSets;

所以我在c#private List

and later in code he use a function with return type bool and he use a method

后来在代码中他使用了返回类型为bool的函数,并使用了一个方法

return DBMSResultSets(I).Read

so i use the same thing but visual studio give me error so hover on vb code (DBMSResultSets(I).Read)it say "get or set the element at the specified index"

所以我使用相同的东西但视觉工作室给我错误所以悬停在vb代码(DBMSResultSets(I).Read)它说“获取或设置指定索引处的元素”

so i look around and find out that if i write return DBMSResultSets[(int)I]); it do the same thing which is ("get or set the element at the specified index")

所以我环顾四周,发现如果我写回DBMSResultSets [(int)I]);它做同样的事情(“获取或设置指定索引处的元素”)

now visual studio give me error that can not convert object to bool so i use convert.to and also try the (bool) mean try to typecast but both method didn't work so i need help i am giving you the whole vb code and also my conversion c# code

现在visual studio给我错误,无法将对象转换为bool所以我使用convert.to并尝试(bool)意味着尝试类型转换但两种方法都不起作用所以我需要帮助我给你整个vb代码和还有我的转换c#代码

the problem is in function ReadAndNotEOF

问题在于函数ReadAndNotEOF

vb code

Imports System.Data.SqlClient

    ' this class will be used to manage connectivity with the database
    Public Class DBMSClass

        ' define the connection string
        Private DBMSConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Asus\Desktop\LibraryManagementSystem\Database\LMS.mdf;Integrated Security=True;User Instance=True;MultipleActiveResultSets=true"

        ' define the connection
        Private DBMSConnectionObj As System.Data.SqlClient.SqlConnection

        ' define the transaction
        Private DBMSTransactionObj As System.Data.SqlClient.SqlTransaction

        ' define the commands object and result sets
        Private DBMSCommands As List(Of System.Data.SqlClient.SqlCommand)
        Private DBMSCommandCodes As List(Of Long)
        Private DBMSResultSets As List(Of Object)

        ' command counter
        Private DBMSCommandCounter As Long

        ' open database connection
        Public Function OpenDB() As String
            Try
                ' open the connection
                DBMSConnectionObj = New SqlConnection(My.Settings.myconnection)
                DBMSConnectionObj.Open()

                ' create the transaction
                DBMSTransactionObj = DBMSConnectionObj.BeginTransaction

                ' prepare the commands list
                DBMSCommands = New List(Of System.Data.SqlClient.SqlCommand)
                DBMSCommandCodes = New List(Of Long)
                DBMSResultSets = New List(Of Object)

                ' prepare the command counter
                DBMSCommandCounter = 0

                ' return ok
                Return "OK"
            Catch ex As Exception
                Return ex.Message
            End Try
        End Function

        ' this is used to run sql commands
        Public Sub ExecuteSQL(ByVal SQL As String, ByVal ParamArray Obj() As Object)

            ' build the command object
            Dim CMD As New System.Data.SqlClient.SqlCommand(SQL, Me.DBMSConnectionObj, Me.DBMSTransactionObj)

            ' add the parameters to the sql command
            Dim I As Integer
            For I = 0 To Obj.Length - 1
                CMD.Parameters.AddWithValue("@" & I, Obj(I))
            Next

            ' run the sql
            CMD.ExecuteNonQuery()

        End Sub

        ' this function is used to commit a transaction
        Public Sub Commit()
            Me.DBMSTransactionObj.Commit()
            Me.DBMSTransactionObj = Me.DBMSConnectionObj.BeginTransaction
        End Sub

        ' this function is used to rollback a transaction
        Public Sub Rollback()
            Me.DBMSTransactionObj.Rollback()
            Me.DBMSTransactionObj = Me.DBMSConnectionObj.BeginTransaction
        End Sub

        ' this function is used to create a result set
        Public Function CreateResultSet(ByVal SQL As String, ByVal ParamArray OBJ() As Object) As Long
            DBMSCommandCounter += 1

            ' build the command object
            Dim CMD As New System.Data.SqlClient.SqlCommand(SQL, Me.DBMSConnectionObj, Me.DBMSTransactionObj)

            ' add the parameters to the sql command
            Dim I As Integer
            For I = 0 To OBJ.Length - 1
                CMD.Parameters.AddWithValue("@" & I, OBJ(I))
            Next

            ' read the data
            Dim RS = CMD.ExecuteReader(CommandBehavior.Default)

            ' store objects in list
            Me.DBMSCommandCodes.Add(DBMSCommandCounter)
            Me.DBMSCommands.Add(CMD)
            Me.DBMSResultSets.Add(RS)

            Return DBMSCommandCounter
        End Function

        ' this function is used to close a result set
        Public Sub CloseResultSet(ByVal Nmbr As Long)
            Dim I As Integer
            For I = 0 To Me.DBMSCommandCodes.Count - 1

                ' find the command and result set
                If DBMSCommandCodes(I) = Nmbr Then

                    ' get the objects
                    Dim R = Me.DBMSResultSets(I)
                    Dim C = Me.DBMSCommands(I)

                    ' remove the objects from the list
                    Me.DBMSResultSets.RemoveAt(I)
                    Me.DBMSCommands.RemoveAt(I)
                    Me.DBMSCommandCodes.RemoveAt(I)

                    ' return the resources
                    R.Close()
                    R.Dispose()
                    C.Dispose()

                    Return

                End If
            Next

            Throw New Exception("the command or result set does not exist")
        End Sub

        ' this function is used to read a single record from db
        Public Function ReadAndNotEOF(ByVal Code As Long) As Boolean
            ' do a search
            Dim I As Long
            For I = 0 To Me.DBMSCommandCodes.Count - 1
                If DBMSCommandCodes(I) = Code Then
                    Return DBMSResultSets(I).Read
                End If
            Next
            Throw New Exception("Command or Resultset does not exist")
        End Function

        ' this function is used to get a column value from db
        Public Function GetColumnValue(ByVal Code As Long, ByVal ColumnName As String) As Object
            Dim I As Long
            For I = 0 To Me.DBMSCommands.Count - 1
                If DBMSCommandCodes(I) = Code Then
                    Return DBMSResultSets(I).Item(ColumnName)
                End If
            Next
            Throw New Exception("Command or Resultset does not exist")
        End Function
    End Class

my c# code

我的c#代码

//this class will be used to manage connectivity with the database
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Sql;
using System.Data;
using System.Data.SqlClient;

namespace Library_main
{
    public class DBMSClass
    {
        //define the connection string

        // private String DBMSConnectionString = "Data Source=(LocalDB)\\v11.0;AttachDbFilename="\\D:\\tutorial\\c # tutorial\\3 may 2015\\Library_main\\Library_main\\bin\\Debug\\DataBase\\LMS.mdf";"Integrated Security=True;Connect Timeout=30";
        //define the connection
        private SqlConnection DBMSConnectionObj = null;
        //define the transaction
        private SqlTransaction DBMSTransactionObj;

        // define the commands object and result sets
        private List<SqlCommand> DBMSCommands;
        private List<long> DBMSCommandCodes;
        private List<object> DBMSResultSets;
        // command counter
        private long DBMSCommandCounter;

        //open database connection
        public string OpenDB()
        {
            try
            {
                //open the connection
                DBMSConnectionObj = new SqlConnection(Properties.Settings.Default.ConnectionString);
                DBMSConnectionObj.Open();
                //creat the transaction
                DBMSTransactionObj = DBMSConnectionObj.BeginTransaction();
                //prepare the commands list
                DBMSCommands = new List<SqlCommand>();
                DBMSCommandCodes = new List<long>();
                DBMSResultSets = new List<object>();
                // prepare the command counter
                DBMSCommandCounter = 0;
                //return ok
                return "ok";
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }

        //this is used to run sql commands
        public void ExceuteSQL(string SQL, params object[] Obj)
        {
            //build the command object
            SqlCommand CMD = new SqlCommand(SQL, this.DBMSConnectionObj, this.DBMSTransactionObj);

            //add the parameters to the sql command
            int I;
            int count = Obj.Length - 1;
            for (I = 0; I <= count; I++)
            {
                CMD.Parameters.AddWithValue("@" + I, Obj[I]);
            }
            //run the sql
            CMD.ExecuteNonQuery();
        }

        //this funtion to commit 
        public void Commit()
        {
            this.DBMSTransactionObj.Commit();
            this.DBMSTransactionObj = this.DBMSConnectionObj.BeginTransaction();
        }

        // this function is used to rollback a transaction
        public void Rollback()
        {
            this.DBMSTransactionObj.Rollback();
            this.DBMSTransactionObj = this.DBMSConnectionObj.BeginTransaction();
        }

        //this function is used to creat a result set
        public long CreatResultSet(string SQL, params object[] Obj)
        {
            DBMSCommandCounter += 1;
            // build the command object
            SqlCommand CMD = new SqlCommand(SQL, this.DBMSConnectionObj, this.DBMSTransactionObj);

            // add the parameters to the sql command
            int I = 0;
            for (I = 0; I <= Obj.Length - 1; I++)
            {
                CMD.Parameters.AddWithValue("@" + I, Obj[I]);
            }
                // read the data
                dynamic RS = CMD.ExecuteReader(System.Data.CommandBehavior.Default);

                // store objects in list
                this.DBMSCommandCodes.Add(DBMSCommandCounter);
                this.DBMSCommands.Add(CMD);
                this.DBMSResultSets.Add(RS);
            return DBMSCommandCounter;
        }

        // this function is used to close a result set
        public void CloseResultSet(long Nmbr)
        {
            int I = 0;

            for (I = 0; I <= this.DBMSCommandCodes.Count - 1; I++)
            {
                // find the command and result set

                if (DBMSCommandCodes[I] == Nmbr)
                {
                    // get the objects
                    dynamic R = this.DBMSResultSets[I];
                    dynamic C = this.DBMSCommands[I];

                    // remove the objects from the list
                    this.DBMSResultSets.RemoveAt(I);
                    this.DBMSCommands.RemoveAt(I);
                    this.DBMSCommandCodes.RemoveAt(I);

                    // return the resources
                    R.Close();
                    R.Dispose();
                    C.Dispose();
                    return;
                }
            }
            throw new Exception("the command or result set does not exist");
        }

        // this function is used to read a single record from db
        public bool ReadAndNotEOF(long Code)
        {
            // do a search
            long I = 0;
            for (I = 0; I <= this.DBMSCommandCodes.Count - 1; I++)
            {
                if (DBMSCommandCodes[(int)I] == Code)
                {
                    return Convert.ToBoolean(DBMSResultSets[(int)I]);
                }
            }
            throw new Exception("Command or Resultset does not exist");
        }

        // this function is used to get a column value from db
        public object GetColumnValue(long Code, string ColumnName)
        {
            long I = 0;
            for (I = 0; I <= this.DBMSCommandCodes.Count - 1; I++)

                if (DBMSCommandCodes[(int)I] == Code)
                {
                    return DBMSResultSets[(int)I].Equals(ColumnName);
                }

            throw new Exception("Command or Resultset does not exist");
        }

    }
}

1 个解决方案

#1

The result of calling executeReader on an SqlCommand object is a SqlDataReader

在SqlCommand对象上调用executeReader的结果是SqlDataReader

See here

In this part of your code

在这部分代码中

// read the data
dynamic RS = CMD.ExecuteReader(System.Data.CommandBehavior.Default);

// store objects in list
this.DBMSCommandCodes.Add(DBMSCommandCounter);
this.DBMSCommands.Add(CMD);
this.DBMSResultSets.Add(RS);

The type of RS is not the exact equivalent of a ResultSetlike the accrostic suggests but it is a SqlDataReaderwhich has a boolean method call Readand it will return true until there is no more datas to fetch from its stream

RS的类型并不是结果集的完全等价,就像应用程序所暗示的那样,但它是一个SqlDataReader,它有一个布尔方法调用Readand它将返回true,直到没有更多的数据从其流中获取

So here in your boolean method called ReadAndNotEofinstead of

所以在这里你的布尔方法叫做ReadAndNotEofinstead of

return Convert.ToBoolean(DBMSResultSets[(int)I]);

SqlDataReader reader = (SqlDataReader)DBMSResultSets[(int)I];
return reader.Read();

On the same pattern you can get the column value in your method GetColumnValue if your change:

在相同的模式下,如果您的更改,您可以在方法GetColumnValue中获取列值:

return DBMSResultSets[(int)I].Equals(ColumnName);

SqlDataReader reader = (SqlDataReader)DBMSResultSets[(int)I];

object columnValue = reader[columnName];
return columnValue;

See here on msdn for the definition of the accessor this (brackets like reader[string_value]) that takes a string parameter (the column name)

请参阅msdn,了解访问器的定义(括号如reader [string_value]),它带有一个字符串参数(列名)

Of course you need to be sure that the Read method of your SqlDataReader has returned true (your above method)

当然你需要确保你的SqlDataReader的Read方法返回true(你的上面的方法)

Hope this helps you.

希望这对你有所帮助。

1 个解决方案

#1

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