The following sample code demonstrates how to select all of the objects on a specified layer.

C++

  CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
  {
    // Get a reference to the layer table
    CRhinoLayerTable& layer_table = context.m_doc.m_layer_table;
    // Get the current layer
    const CRhinoLayer& current_layer = layer_table.CurrentLayer();


    // Prompt for a layer name
    CRhinoGetString gs;
    gs.SetCommandPrompt( L"Name of layer to select object" );
    gs.SetDefaultString( current_layer.LayerName() );
    gs.AcceptNothing( TRUE );
    gs.GetString();
    if( gs.CommandResult() != CRhinoCommand::success )
      return gs.CommandResult();


    // Validate the string
    ON_wString layer_name = gs.String();
    layer_name.TrimLeftAndRight();
    if( layer_name.IsEmpty() )
      return CRhinoCommand::cancel;


    // Find the layer
    int layer_index = layer_table.FindLayer( layer_name );
    if( layer_index < 0 )
    {
      RhinoApp().Print( L"\"%s\" does not exists.\n", layer_name );
      return CRhinoCommand::cancel;
    }


    // Get the layer
    const CRhinoLayer& layer = layer_table[layer_index];


    // Get all of the objects on the layer
    ON_SimpleArray<CRhinoObject*> obj_list;
    int i, obj_count = context.m_doc.LookupObject( layer, obj_list );


    // Select all of the layer objects
    for( i = 0; i < obj_count; i++ )
    {
      CRhinoObject* obj = obj_list[i];
      if( obj && obj->IsSelectable() )
        obj->Select();
    }


    if( obj_count )
      context.m_doc.Redraw();
    return CRhinoCommand::success;
  }

VB.NET (Rhino 4)

  Public Overrides Function RunCommand(ByVal context As IRhinoCommandContext)_
    As IRhinoCommand.result


    ' Get a reference to the layer table
    Dim layer_table As MRhinoLayerTable = context.m_doc.m_layer_table
    ' Get the current layer
    Dim current_layer As IRhinoLayer = layer_table.CurrentLayer()


    ' Prompt for a layer name
    Dim gs As New MRhinoGetString()
    gs.SetCommandPrompt("Name of layer to select object")
    gs.SetDefaultString(current_layer.LayerName())
    gs.AcceptNothing(True)
    gs.GetString()
    If (gs.CommandResult() <> IRhinoCommand.result.success) Then Return gs.CommandResult()


    ' Validate the string
    Dim layer_name As String = gs.String().Trim()
    If (String.IsNullOrEmpty(layer_name)) Then
      Return IRhinoCommand.result.cancel
    End If


    ' Find the layer
    Dim layer_index As Integer = layer_table.FindLayer(layer_name)
    If (layer_index < 0) Then
      RhUtil.RhinoApp.Print(layer_name + "does not exist." + vbCrLf)
      Return IRhinoCommand.result.cancel
    End If


    ' Get the layer
    Dim layer As IRhinoLayer = layer_table(layer_index)


    ' Get all of the objects on the layer
    Dim obj_list As MRhinoObject() = Nothing
    Dim obj_count As Integer = context.m_doc.LookupObject(layer, obj_list)


    ' Select all of the layer objects
    If (obj_list Is Nothing) Then Return IRhinoCommand.result.cancel


    For Each obj As MRhinoObject In obj_list
      If (obj IsNot Nothing And obj.IsSelectable()) Then obj.Select()
    Next


    If (obj_count > 0) Then context.m_doc.Redraw()
    Return IRhinoCommand.result.success
  End Function

C# (Rhino 4)

  public override IRhinoCommand.result RunCommand(IRhinoCommandContext context)
  {
    // Get a reference to the layer table
    MRhinoLayerTable layer_table = context.m_doc.m_layer_table;
    // Get the current layer
    IRhinoLayer current_layer = layer_table.CurrentLayer();


    // Prompt for a layer name
    MRhinoGetString gs = new MRhinoGetString();
    gs.SetCommandPrompt("Name of layer to select object");
    gs.SetDefaultString(current_layer.LayerName());
    gs.AcceptNothing(true);
    gs.GetString();
    if(gs.CommandResult() != IRhinoCommand.result.success)
      return gs.CommandResult();


    // Validate the string
    string layer_name = gs.String().Trim();
    if(string.IsNullOrEmpty(layer_name))
      return IRhinoCommand.result.cancel;


    // Find the layer
    int layer_index = layer_table.FindLayer(layer_name);
    if(layer_index < 0)
    {
      RhUtil.RhinoApp().Print(layer_name + "does not exist.\n");
      return IRhinoCommand.result.cancel;
    }


    // Get the layer
    IRhinoLayer layer = layer_table[layer_index];


    // Get all of the objects on the layer
    MRhinoObject[] obj_list = null;
    int obj_count = context.m_doc.LookupObject(layer, ref obj_list);


    // Select all of the layer objects
    if(obj_list == null)
      return IRhinoCommand.result.cancel;


    foreach( MRhinoObject obj in obj_list)
    {
      if( obj != null && obj.IsSelectable() )
        obj.Select();
    }


    if (obj_count > 0)
      context.m_doc.Redraw();
    return IRhinoCommand.result.success;
  }