Programmatically getting the current Visual Studio IDE solution directory from addins

EnvDTE.DTE dte = (EnvDTE.DTE)System.Runtime.InteropServices.Marshal.GetActiveObject("VisualStudio.DTE"); string solutionDir = System.IO.Path.GetDirectoryName(dte.Solution.FullName);

But, this returns the solution directory for the add ins, not the current solution.

Your approach to get the directory is good. What's wrong is the way you get the VisualStudio.DTE object. Where is this code called? I assume it is in your add-in. Do you execute (debug) your add-in in Visual Studio which opens another instance of Visual Studio where you open your solution? So you have two instances of Visual Studio.

The GetActiveObject("VisualStudio.DTE") gets a random Visual Studio instance. In your case, it is apparently Visual Studio with an add-in project since you get path to your add-in. That's for explanation what would be the reason of your problem.

The correct way to get DTE is very simple. In fact, your add-in already has reference to DTE in which it runs (that is, in which the solution is opened). It is stored in a global variable _applicationObject in your add-in connect class. It is set when your add-in starts in the OnConnection event handler. So all you need is to call:

string solutionDir = System.IO.Path.GetDirectoryName(_applicationObject.Solution.FullName);

With Peter's push in the right direction, I set up the context menu addin to launch an external tool with the solution directory, and output the results to the output pane. Some example blurb from the add in:

    ///--------------------------------------------------------------------------------
    /// <summary>This method implements the OnConnection method of the IDTExtensibility2 interface. Receives notification that the Add-in is being loaded.</summary>
    ///
    /// <param term='application'>Root object of the host application.</param>
    /// <param term='connectMode'>Describes how the Add-in is being loaded.</param>
    /// <param term='addInInst'>Object representing this Add-in.</param>
    /// <seealso class='IDTExtensibility2' />
    ///--------------------------------------------------------------------------------
    public void OnConnection(object application, ext_ConnectMode connectMode, object addInInst, ref Array custom)
    {
        _applicationObject = (DTE2)application;
        _addInInstance = (AddIn)addInInst;

        // Get the solution command bar
        CommandBar solutionCommandBar = ((CommandBars)_applicationObject.CommandBars)["Solution"];

        // Set up the main InCode
        CommandBarPopup solutionPopup = (CommandBarPopup)solutionCommandBar.Controls.Add(MsoControlType.msoControlPopup, System.Reflection.Missing.Value, System.Reflection.Missing.Value, 1, true);
        solutionPopup.Caption = "InCode";

        // Add solution updater submenu
        CommandBarControl solutionUpdaterControl = solutionPopup.Controls.Add(MsoControlType.msoControlButton, System.Reflection.Missing.Value, System.Reflection.Missing.Value, 1, true);
        solutionUpdaterControl.Caption = "Update Solution";
        updateSolutionMenuItemHandler = (CommandBarEvents)_applicationObject.Events.get_CommandBarEvents(solutionUpdaterControl);
        updateSolutionMenuItemHandler.Click += new _dispCommandBarControlEvents_ClickEventHandler(updateSolution_Click);
    }

    // The event handlers for the solution submenu items
    CommandBarEvents updateSolutionMenuItemHandler;

    ///--------------------------------------------------------------------------------
    /// <summary>This property gets the solution updater output pane.</summary>
    ///--------------------------------------------------------------------------------
    protected OutputWindowPane _solutionUpdaterPane = null;
    protected OutputWindowPane SolutionUpdaterPane
    {
        get
        {
            if (_solutionUpdaterPane == null)
            {
                OutputWindow outputWindow = _applicationObject.ToolWindows.OutputWindow;
                foreach (OutputWindowPane loopPane in outputWindow.OutputWindowPanes)
                {
                    if (loopPane.Name == "Solution Updater")
                    {
                        _solutionUpdaterPane = loopPane;
                        return _solutionUpdaterPane;
                    }
                }
                _solutionUpdaterPane = outputWindow.OutputWindowPanes.Add("Solution Updater");
            }
            return _solutionUpdaterPane;
        }
    }

    ///--------------------------------------------------------------------------------
    /// <summary>This method handles clicking on the Update Solution submenu.</summary>
    ///
    /// <param term='inputCommandBarControl'>The control that is source of the click.</param>
    /// <param term='handled'>Handled flag.</param>
    /// <param term='cancelDefault'>Cancel default flag.</param>
    ///--------------------------------------------------------------------------------
    protected void updateSolution_Click(object inputCommandBarControl, ref bool handled, ref bool cancelDefault)
    {
        try
        {
            // set up and execute solution updater thread
            UpdateSolutionDelegate updateSolutionDelegate = UpdateSolution;
            updateSolutionDelegate.BeginInvoke(UpdateSolutionCompleted, updateSolutionDelegate);
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }

    protected delegate void UpdateSolutionDelegate();

    ///--------------------------------------------------------------------------------
    /// <summary>This method launches the solution updater to update the solution.</summary>
    ///--------------------------------------------------------------------------------
    protected void UpdateSolution()
    {
        try
        {
            // set up solution updater process
            string solutionDir = System.IO.Path.GetDirectoryName(_applicationObject.Solution.FullName);
            System.Diagnostics.ProcessStartInfo procStartInfo = new System.Diagnostics.ProcessStartInfo(@"SolutionUpdater.exe", solutionDir);
            procStartInfo.RedirectStandardOutput = true;
            procStartInfo.UseShellExecute = false;
            procStartInfo.CreateNoWindow = true;
            System.Diagnostics.Process proc = new System.Diagnostics.Process();
            proc.StartInfo = procStartInfo;

            // execute the solution updater
            proc.Start();

            // put solution updater output to output pane
            SolutionUpdaterPane.OutputString(proc.StandardOutput.ReadToEnd());
            SolutionUpdaterPane.OutputString("Solution update complete.");
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }

    ///--------------------------------------------------------------------------------
    /// <summary>This method completing the update solution thread.</summary>
    ///
    /// <param name="ar">IAsyncResult.</param>
    ///--------------------------------------------------------------------------------
    protected void UpdateSolutionCompleted(IAsyncResult ar)
    {
        try
        {
            if (ar == null) throw new ArgumentNullException("ar");

            UpdateSolutionDelegate updateSolutionDelegate = ar.AsyncState as UpdateSolutionDelegate;
            Trace.Assert(updateSolutionDelegate != null, "Invalid object type");

            updateSolutionDelegate.EndInvoke(ar);
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }