WinForms-UserControl-列表 <bool> 集合 <bool> 作为UserControl的可浏览属性

Question

Why the MessageBox and CheckBox apprears in Design-Time when changing value of the First property and do not when adding item to Second?

    private string _first;
    [Description(""), Category("GostcompSettings"), DefaultValue("27017")]
    public string First
    {
        get { return __first; }
        set
        {

            _searchAreasChceckBoxList.Clear();
            pPanelWithCheckboxies.Controls.Clear();
            int x = 10;
            int y = 10;

            CheckBox _tempCheck = new CheckBox();
            _tempCheck.Checked = true;
            _tempCheck.Location = new Point(x, y);

            _searchAreasChceckBoxList.Add(_tempCheck);
            pPanelWithCheckboxies.Controls.Add(_tempCheck);

            MessageBox.Show("zmiana");
            _first = value;
        }
    }


    private Collection<bool> _second= new Collection<bool>();
    [Description(""), Category("*")]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
    public Collection<bool> Second
    {
        get
        {
            return _second;
        }
        set
        {

            _searchAreasChceckBoxList.Clear();
            pPanelWithCheckboxies.Controls.Clear();
            int x = 10;
            int y = 10;

            CheckBox _tempCheck = new CheckBox();
            _tempCheck.Checked = true;
            _tempCheck.Location = new Point(x, y);

            _searchAreasChceckBoxList.Add(_tempCheck);
            pPanelWithCheckboxies.Controls.Add(_tempCheck);

            MessageBox.Show("*");
            _second= value;
        }
    }

It's the same scenario when I change Collection to List... Values are kept (or added to Collection in Second case) and designer generate code for InitializeComponent().

EDIT after @taffer answear

public class SearchAreaInfo
{
    public SearchAreasEnum searchArea
    {
        get; set;
    }
}

public class SearchAreaInfoCollection : Collection<SearchAreaInfo>
{
    private Panel _checkboxParent;

    public SearchAreaInfoCollection(Panel checkboxParent) : base()
    {
        _checkboxParent = checkboxParent;
    }

    // called on Add/Insert
    protected override void InsertItem(int index, SearchAreaInfo item)
    {
        base.InsertItem(index, item);
        RepaintChackboxPanel();
    }

    // called on Remove/RemoveAt
    protected override void RemoveItem(int index)
    {
        base.RemoveItem(index);
        RepaintChackboxPanel();
    }

    // called when an element is set by the indexer
    protected override void SetItem(int index, SearchAreaInfo item)
    {
        base.SetItem(index, item);
        RepaintChackboxPanel();
    }

    private void RepaintChackboxPanel()
    {
        //_searchAreasChceckBoxList.Clear();
        _checkboxParent.Controls.Clear();
        int x = 0;
        int y = 0;

        foreach (var item in this)
        {
            CheckBox _tempCheck = new CheckBox();
            _tempCheck.Checked = true;
            _tempCheck.Location = new Point(x, y);
            _tempCheck.BringToFront();

            //_searchAreasChceckBoxList.Add(_tempCheck);
            _checkboxParent.Controls.Add(_tempCheck);                
            x += 5;
            y += 5;
        }
        _checkboxParent.Invalidate();
    }
}

    private SearchAreaInfoCollection _searchAreas;
    [Description(""), Category("GostcompSettings")]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
    public SearchAreaInfoCollection SearchAreas
    {
        get
        {
            return _searchAreas;
        }
    }

Now the prooblem is that: when I add let's say third item to the collection in Editor it draws only one checkbox but should draw 3 checkboxes... Moreover in debugging I see that foreach loop goes then 3 times: 1st collection has 1 item , 2nd time collection has 2 items and third time collection has 3 items, but finally I see just one checkbox in _checkboxPanel.

Answer 1

Because the setter of Second property is executed only when you replace the whole collection. When you add/remove an item, the getter returns your collection instance ( _second ), and the Add / Remove method will be called on that object instance.

If you want to perform checks on element addition/removal, create a custom collection type instead:

public class MyBoolCollection: Collection<bool>
{
    // called on Add/Insert
    protected override void InsertItem(int index, bool item)
    {
        // do some checks here
        base.InsertItem(index, item);
    }

    // called on Remove/RemoveAt
    protected override void RemoveItem(int index)
    {
        // do some checks here
        base.RemoveItem(index, item);
    }

    // called when an element is set by the indexer
    protected override void SetItem(int index, bool item)
    {
        // do some checks here
        base.SetItem(index, item);
    }
}

Answer 2

The built-in collection editor that you are using now only changes the content of your collection object. Which works fine, but does not get your setter called at all. In other words, it never creates a new collection object, nor does it know how to do that.

To get your property setter called, you have to create your own UITypeEditor and have it return a new collection from its EditValue() method override. Pretty easy to do, first add a reference to System.Design, then make your code look similar to this:

using System.Drawing.Design;
...
        [Editor(typeof(MyEditor), typeof(System.Drawing.Design.UITypeEditor))]
        public Collection<bool> Second {
            // etc...
        }

        private class MyEditor : UITypeEditor {
            public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context) {
                return UITypeEditorEditStyle.Modal;
            }
            public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value) {
                var editor = new System.ComponentModel.Design.CollectionEditor(typeof(Collection<bool>));
                var retval = (Collection<bool>)editor.EditValue(context, provider, value);
                return new Collection<bool>(retval);

            }
        }

You probably want to improve this a bit, like implementing your own editor UI so all of those bools are easier to interpret.