Getting Exception "ActiveContent must be one of the visible contents, or null if there is no visible content"

[ChristopherPH]

Hello,

I know this issue has been raised at least twice before now ( #226 #502 ), but I am experiencing this with the following steps:

• The dockpanel is set up with all the content as HideOnClose
• The initial dock layout has a floating window that was not initially docked
• The floating window is then docked (via code or manually)
• The layout is saved
• The window is undocked (via code, manually, or via loading a different saved layout)
• The layout is loaded

Below is a code sample that will reproduce the exception. I am using version 3.04 and 3.10.

I'm hoping that I'm doing something wrong and it isn't a bug, but any help or pointers to get though this would be very much appreciated.

Thanks!

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;
using WeifenLuo.WinFormsUI.Docking;

namespace DockPanelSuiteCrash
{
    public partial class Form1 : Form
    {
        List<DockContent> LocalContent = new List<DockContent>();

        DockContent contentForm = new CustomDockContent()
        {
            Text = "ContentForm",
            Dock = DockStyle.Fill,
            DockAreas = DockAreas.Document,
            ShowHint = DockState.Document,
            HideOnClose = true,
            BackColor = Color.Teal,
        };

        DockContent toolForm = new CustomDockContent()
        {
            Text = "ToolForm",
            Dock = DockStyle.Fill,
            DockAreas = DockAreas.DockLeft | DockAreas.DockRight | DockAreas.DockTop | DockAreas.DockBottom | DockAreas.Float,
            ShowHint = DockState.Float,
            HideOnClose = true,
            Size = new Size(150, 200),
            BackColor = Color.AntiqueWhite,
        };

        static VS2015LightTheme theme = new VS2015LightTheme();

        DockPanel dockPanel = new DockPanel()
        {
            Dock = DockStyle.Fill,
            Theme = theme,
            DocumentStyle = DocumentStyle.DockingSdi,
        };

        public Form1()
        {
            InitializeComponent();
            this.Controls.Add(dockPanel);
            this.PerformLayout();
        }

        public class CustomDockContent : DockContent
        {
            protected override string GetPersistString()
            {
                return this.Text;
            }
        }

        protected override void OnShown(EventArgs e)
        {
            base.OnShown(e);

            LocalContent.Add(toolForm);
            LocalContent.Add(contentForm);

            foreach (var content in LocalContent)
            {
                if (content.ShowHint == DockState.Float)
                {
                    //get dockpanel location on screen to be able to center the floatwindow
                    var location = dockPanel.PointToScreen(dockPanel.Location);

                    //center floatwindow in dockpanel
                    var floatBounds = new Rectangle(
                        (dockPanel.Width / 2) - (content.Width / 2) + location.X,
                        (dockPanel.Height / 2) - (content.Height / 2) + location.Y,
                        content.Width, content.Height);

                    //show floating window
                    content.Show(dockPanel, floatBounds);
                }
                else
                {
                    //show any other content
                    content.Show(dockPanel);
                }
            }

            dockPanel.SaveAsXml("floating.xml");

            toolForm.DockState = DockState.DockTop;

            dockPanel.SaveAsXml("docked.xml");

            LoadLayout("docked.xml"); //This succeeds
            LoadLayout("floating.xml");
            LoadLayout("docked.xml"); //This fails
        }

        void LoadLayout(string filename)
        {
            try
            {
                foreach (var content in LocalContent)
                    content.DockPanel = null;

                foreach (var window in dockPanel.FloatWindows.ToList())
                    window.Close();

                dockPanel.LoadFromXml(filename, (persist) => LocalContent.FirstOrDefault(x => x.Text == persist));
            }
            catch (Exception ex)
            {
                MessageBox.Show(this, ex.Message);
            }
        }
    }
}

[ChristopherPH]

It seems as though this problem goes away if I recreate the DockContent inside LoadFromXml() instead of re-using the saved content.

When comparing the properties of the DockContent from before calling content.Show(dockPanel, floatBounds); to after setting content.DockPanel = null;, I noticed the IsFloat property was not reset back to false.

I was not able to directly set content.IsFloat = false; as setting the property called CheckDockState() which ended up returning DefaultDockState, which ended up returning the ShowHint, which was DockState.Float.

I have been able to work around the problem by temporarily setting the ShowHint to DockState.Unknown, setting IsFloat = false; then setting 'ShowHintback toDockState.Float`.

This seems to stop the exception from happening, from my initial testing.

                foreach (var content in LocalContent)
                {
                    if (content.ShowHint == DockState.Float)
                    {
                        content.ShowHint = DockState.Unknown;
                        content.IsFloat = false;
                        content.ShowHint = DockState.Float;
                    }

                    content.DockPanel = null;
                }