Merge pull request picoe#887 from picoe/fix/wpf-customcell-loading-ex…

…ception

Fix issue with WPF when using a custom cell on a tab.

Source/Eto.Test/Eto.Test/Eto.Test - pcl.csproj

@@ -136,6 +136,7 @@
     <Compile Include="UnitTests\Drawing\GraphicsTests.cs" />
     <Compile Include="UnitTests\Drawing\MatrixTests.cs" />
     <Compile Include="UnitTests\Forms\Controls\ComboBoxTests.cs" />
+    <Compile Include="UnitTests\Forms\Controls\CustomCellTests.cs" />
     <Compile Include="UnitTests\Forms\Controls\NumericStepperTests.cs" />
     <Compile Include="UnitTests\Forms\Controls\PanelTests.cs" />
     <Compile Include="UnitTests\Forms\Controls\SplitterTests.cs" />

Source/Eto.Test/Eto.Test/UnitTests/Forms/Controls/CustomCellTests.cs

@@ -0,0 +1,68 @@
+using Eto.Forms;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Eto.Test.UnitTests.Forms.Controls
+{
+	[TestFixture]
+	public class CustomCellTests : TestBase
+	{
+		class MyModel
+		{
+			public string Text { get; set; }
+		}
+
+		class MyCustomCell : StackLayout
+		{
+			public MyCustomCell()
+			{
+				Orientation = Orientation.Horizontal;
+				Items.Add(new Label { Text = "Hello!" });
+				var tb = new TextBox();
+				tb.TextBinding.BindDataContext((MyModel m) => m.Text);
+				Items.Add(new StackLayoutItem(tb, true));
+			}
+		}
+
+		/// <summary>
+		/// Test for WPF crash when a grid view and custom cell is on a separate tab and you switch to it.
+		/// </summary>
+		[Test]
+		public void CustomCellOnSeparateTabLoadIssue()
+		{
+			TabControl tabs = null;
+			Shown(form =>
+			{
+				var grid1 = new GridView { ShowHeader = false };
+				grid1.Columns.Add(new GridColumn { DataCell = CustomCell.Create<MyCustomCell>() });
+				grid1.DataStore = new List<MyModel>
+				{
+					new MyModel { Text = "Item 1"},
+					new MyModel { Text = "Item 2"},
+					new MyModel { Text = "Item 3"},
+				};
+
+				var grid2 = new GridView { ShowHeader = false };
+				grid2.Columns.Add(new GridColumn { DataCell = CustomCell.Create<MyCustomCell>() });
+				grid2.DataStore = new List<MyModel>
+				{
+					new MyModel { Text = "Item 1"},
+					new MyModel { Text = "Item 2"},
+					new MyModel { Text = "Item 3"},
+				};
+
+				tabs = new TabControl();
+				tabs.Pages.Add(new TabPage(grid1) { Text = "Tab 1" });
+				tabs.Pages.Add(new TabPage(grid2) { Text = "Tab 2" });
+				form.Content = tabs;
+			}, () =>
+			{
+				tabs.SelectedIndex = 1;
+			});
+		}
+	}
+}

Source/Eto.Wpf/Forms/Cells/CustomCellHandler.cs

@@ -82,12 +82,15 @@ EtoBorder Create(swc.DataGridCell cell)
 					control.Unloaded += (sender, e) =>
 					{
 						var ctl = sender as EtoBorder;
-						ctl.Control?.DetachNative();
+						if (ctl.Control.Loaded)
+							ctl.Control?.DetachNative();
 					};
 					control.Loaded += (sender, e) =>
 					{
+						// WPF's loaded event is called more than once, e.g. when on a tab that is not initially visible.
 						var ctl = sender as EtoBorder;
-						ctl.Control?.AttachNative();
+						if (!ctl.Control.Loaded)
+							ctl.Control?.AttachNative();
 					};
 					control.DataContextChanged += (sender, e) =>
 					{