Visual C++ .NET/Development/IAsyncResult

Run Async Command against database

 
#include "stdafx.h"

using namespace System;
using namespace System::Data;
using namespace System::Data::SqlClient;
ref struct MyEventHandler{
    static void CommandCompleted(IAsyncResult^ asyncResult){
        SqlCommand^ asyncCommand = dynamic_cast<SqlCommand^>(asyncResult->AsyncState);
        
        if ( asyncCommand!= nullptr )
            SqlDataReader^ dataReader = asyncCommand->EndExecuteReader(asyncResult);
    }
};
void main()
{
    SqlConnectionStringBuilder^ connectionBuilder = gcnew SqlConnectionStringBuilder();
    connectionBuilder->AsynchronousProcessing = true;
    connectionBuilder->DataSource = "localhost";
    connectionBuilder->InitialCatalog = "myCatalog";
    connectionBuilder->UserID = "sa";
    connectionBuilder->Password = "";
    
    SqlConnection^ myConnection = gcnew SqlConnection(connectionBuilder->ToString());
    myConnection->Open();
    
    SqlCommand^ asyncCommand = myConnection->CreateCommand();
    asyncCommand->CommandText = "SELECT * FROM Music";
    
    AsyncCallback^ asyncCallback = gcnew AsyncCallback(MyEventHandler::CommandCompleted);
    
    IAsyncResult^ asyncResult = asyncCommand->BeginExecuteReader(asyncCallback, asyncCommand);
    
    asyncResult->AsyncWaitHandle->WaitOne();
}

Using IAsyncResult

 
#include "stdafx.h"
using namespace System;
using namespace System::Threading;
ref class MyClass{
public:
   property String^ Value;
   MyClass(String^ s) { Value = s; }
};
delegate void DoSearch(String^, MyClass^);
ref class Database{
   IAsyncResult^ result;
   MyClass^ m_r;
   public:
      Database(String^ s) { m_r = gcnew MyClass(s); }
   void Query(String^ queryString, MyClass^ r){
       r->Value = "New Value";
   }
   void InitiateQuery(String^ queryString){
      DoSearch^ qf = gcnew DoSearch(this, &Database::Query);
      Console::WriteLine(m_r->Value);
      result = qf->BeginInvoke(queryString, m_r,gcnew AsyncCallback(this, &Database::ProcessResult),qf);
   }
   bool IsQueryCompleted(){
      return result->IsCompleted;
   }
   void ProcessResult(IAsyncResult^ result)
   {
      DoSearch^ caller = (DoSearch^) result->AsyncState;
      caller->EndInvoke(result);
      Console::WriteLine(m_r->Value);
   }
};
int main(){
   Database doc("Old Value");
   doc.InitiateQuery("SELECT * FROM Employee ");
   while (! doc.IsQueryCompleted() ){
       Thread::Sleep(100);
   }
}