Transferring Data to the Remote Device

Steps

• Call the CMyOwnLlcpApplication::SendHelloWorldText method as shown in the following code snippet:

  Example:

  // CMyOwnLlcpApplication::SendHelloWorldText()
  // -----------------------------------------------------------------------------
  //
  TInt CMyOwnLlcpApplication::SendHelloWorldText()
      {
      TInt error = KErrNone;
      
      if ( iLocalConnection )
          {
          iLocalConnection->Transfer( iStatus, _L8( "Hello World!" ) );
          SetActive();
          }
      else
          {
          // The LLCP link is not established, cannot send any data.
          error = KErrNotReady;
          }
          
      return error;
      }
  // -----------------------------------------------------------------------------
  // End of CMyOwnLlcpApplication::SendHelloWorldText()
  
  

  Note: If the iLocalConnection object has already been created, the MLlcpConnOrientedTransporter::Transmit() method is called. iLocalConnection is a member variable for the MLlcpConnOrientedTransporter object and created in the CMyOwnLlcpApplication::LlcpRemoteFound method. If iLocalConnection is NULL, the CMyOwnLlcpApplication::LlcpRemoteFound method is not called, and no LLCP link between the local and remote devices is established.

  The actual data transfer in the COwnLlcpConnection::Transfer() method is as shown in the following code snippet:

  // COwnLlcpConnection::Transfer()
  // -----------------------------------------------------------------------------
  //
  void COwnLlcpConnection::Transfer( TRequestStatus& aStatus, const TDesC8& aData )
      {
      TInt error = KErrNone;
      aStatus = KRequestPending;
      TRequestStatus* status = &aStatus // local
      
      // Copy the data to an internal buffer. 
      iTransmitBuf.Zero();
      error = iTransmitBuf.ReAlloc( aData.Length() );
      
      if ( error == KErrNone )
          {
          iTransmitBuf.Append( aData );
          
          if ( iConnState == ENotConnected )
              {
              // Start connecting if the connection is in idle state
              iConnection->Connect( iStatus );
              SetActive();
              iConnState = EConnecting;
              
              iClientStatus = status;
              }
          else if ( iConnState == EConnected && iActionState == EIdle )
              {
              // Send the data.
              iConnection->Transmit( iStatus, iTransmitBuf );
              SetActive();
              iActionState = ETransmitting;
              
              iClientStatus = status;
              }
          else
              {
              // iConnState == EConnecting, cannot do anything.
              error = KErrInUse;
              }
          }
          
      if ( error != KErrNone )
          {
          User::RequestComplete( status, error );
          }
      }
  // -----------------------------------------------------------------------------
  // End of COwnLlcpConnection::Transfer()

  The COwnLlcpConnection::Transfer() method copies descriptor to its internal buffer and then data transfer occurs immediately between local and remote device.

  Note:

  • The COwnLlcpConnection::Transfer() method cannot start transferring data if there is a pending transfer or receive request. In such a scenario, KErrInUse is returned. This means that COwnLlcpConnection object does not support simultaneous transfer and receipt. However, MLlcpConnOrientedTransporter supports simultaneous data transfer and receipt between the local and remote devices.

  • If the COwnLlcpConnection object is not connected, COwnLlcpConnection requests the MLlcpConnOrientedTransporter::Connect() method. When MLlcpConnOrientedTransporter is connected, COwnLlcpConnection::RunL() method is called as shown in the following code snippet.

    // Handling the connecting request
            case EConnecting:
                {
                if ( error == KErrNone )
                    {
                    // Update the state
                    iConnState = EConnected;
                    
                    // Send the data if there is data to send
                    if ( iTransmitBuf.Length() > 0 )
                        {
                        iConnection->Transmit( iStatus, iTransmitBuf );
                        SetActive();
                        iActionState = ETransmitting;
                        }
                    }
                else
                    {
                    if ( iClientStatus )
                        {
                        User::RequestComplete( iClientStatus, error );
                        iClientStatus = NULL;
                        }
                    
                    iConnState = ENotConnected;
                    }
                }
                break;
            // End of handling the connecting request
    

    If a connection request is successfully completed, actual data transfer will be issued through MLlcpConnOrientedTransporter::Tranmit().

  • The maximum amount of data that MLlcpConnOrientedTransporter::Transmit()can handle is the value returned by the MLlcpConnOrientedTransporter::SupportedDataLength() method. If the data is greater than the value, clients of MLlcpConnOrientedTransporter::Transmit() must send data in multiple packets. The minimum size of MLlcpConnOrientedTransporter::SupportedDataLength() is 128 bytes.

  The following diagram illustrates the sequence diagram of data transferring:

  

  Figure: Sequence diagram of data transferring