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copied!<p>You can create your own collection editor, and hook into events on the default editor's controls. You can use these events to, say, disable the OK button. Something like:</p> <pre><code>public class MyCollectionEditor : CollectionEditor { private static Dictionary<CollectionForm, Button> okayButtons = new Dictionary<CollectionForm, Button>(); // Inherit the default constructor from CollectionEditor public MyCollectionEditor(Type type) : base(type) { } // Override this method in order to access the containing user controls // from the default Collection Editor form or to add new ones... protected override CollectionForm CreateCollectionForm() { CollectionForm collectionForm = base.CreateCollectionForm(); collectionForm.FormClosed += new FormClosedEventHandler(collectionForm_FormClosed); collectionForm.Load += new EventHandler(collectionForm_Load); if (collectionForm.Controls.Count > 0) { TableLayoutPanel mainPanel = collectionForm.Controls[0] as TableLayoutPanel; if ((mainPanel != null) && (mainPanel.Controls.Count > 7)) { // Get a reference to the inner PropertyGrid and hook // an event handler to it. PropertyGrid propertyGrid = mainPanel.Controls[5] as PropertyGrid; if (propertyGrid != null) { propertyGrid.PropertyValueChanged += new PropertyValueChangedEventHandler( propertyGrid_PropertyValueChanged); } // Also hook to the Add/Remove TableLayoutPanel buttonPanel = mainPanel.Controls[1] as TableLayoutPanel; if ((buttonPanel != null) && (buttonPanel.Controls.Count > 1)) { Button addButton = buttonPanel.Controls[0] as Button; if (addButton != null) { addButton.Click += new EventHandler(addButton_Click); } Button removeButton = buttonPanel.Controls[1] as Button; if (removeButton != null) { removeButton.Click += new EventHandler(removeButton_Click); } } // Find the OK button, and hold onto it. buttonPanel = mainPanel.Controls[6] as TableLayoutPanel; if ((buttonPanel != null) && (buttonPanel.Controls.Count > 1)) { Button okayButton = buttonPanel.Controls[0] as Button; if (okayButton != null) { okayButtons[collectionForm] = okayButton; } } } } return collectionForm; } private static void collectionForm_FormClosed(object sender, FormClosedEventArgs e) { CollectionForm collectionForm = (CollectionForm)sender; if (okayButtons.ContainsKey(collectionForm)) { okayButtons.Remove(collectionForm); } } private static void collectionForm_Load(object sender, EventArgs e) { ValidateEditValue((CollectionForm)sender); } private static void propertyGrid_PropertyValueChanged(object sender, PropertyValueChangedEventArgs e) { ValidateEditValue((CollectionForm)sender); } private static void addButton_Click(object sender, EventArgs e) { Button addButton = (Button)sender; ValidateEditValue((CollectionForm)addButton.Parent.Parent.Parent); } private static void removeButton_Click(object sender, EventArgs e) { Button removeButton = (Button)sender; ValidateEditValue((CollectionForm)removeButton.Parent.Parent.Parent); } private static void ValidateEditValue(CollectionForm collectionForm) { if (okayButtons.ContainsKey(collectionForm)) { Button okayButton = okayButtons[collectionForm]; IList<MyClass> items = collectionForm.EditValue as IList<MyClass>; okayButton.Enabled = MyCollectionIsValid(items); } } private static bool MyCollectionIsValid(IList<MyClass> items) { // Perform validation here. return (items.Count == 2); } } </code></pre> <p>You will also need to add an Editor attribute to you collection:</p> <pre><code>class MyClass { [Editor(typeof(MyCollectionEditor), typeof(System.Drawing.Design.UITypeEditor))] List<Foo> MyCollection { get; set; } } </code></pre> <p><strong>NOTE:</strong> I found that the value of items in removeButton_Click was not correct - so some tweaking may need to take place.</p>

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