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Fix Up and Down arrow buttons not disabling at first and last items in Collection Editor #14668

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Fix Up and Down arrow buttons not disabling at first and last items in Collection Editor #14668

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e6f5d7b
Fix_Issue_3152: Disable Up and Down buttons correctly in CollectionEd…
Rabina4363sf May 26, 2026
267e52d
Fix_Issue_3152 - Added testcases for the CollectionEditor Form's Up a…
Rabina4363sf Jun 23, 2026
aac2f7f
Merge branch 'dotnet:main' into Fix_Issue_3152
Rabina4363sf Jun 23, 2026
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6 changes: 4 additions & 2 deletions ...esign/src/System/ComponentModel/Design/CollectionEditor.CollectionEditorCollectionForm.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1037,9 +1037,11 @@ private void UpdateEnabled()
}

bool editEnabled = (_listBox.SelectedItem is not null) && CollectionEditable;
int count = _listBox.Items.Count;
int selectedIndex = _listBox.SelectedIndex;
_removeButton.Enabled = editEnabled && AllowRemoveInstance(((ListItem)_listBox.SelectedItem!).Value);
_upButton.Enabled = editEnabled && _listBox.Items.Count > 1;
_downButton.Enabled = editEnabled && _listBox.Items.Count > 1;
_upButton.Enabled = editEnabled && count > 1 && selectedIndex > 0;
_downButton.Enabled = editEnabled && count > 1 && selectedIndex < count - 1;
_propertyGrid.Enabled = editEnabled;
_addButton.Enabled = CollectionEditable;

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35 changes: 35 additions & 0 deletions ...indows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs
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Expand Up @@ -15,6 +15,41 @@ namespace System.ComponentModel.Design.Tests;

public class CollectionEditorTests
{
[Fact]
public void CollectionEditor_CollectionForm_UpdateEnabled_FirstMiddleLastNone_SetsUpDownExpected()
{
SubCollectionEditor editor = new(typeof(List<int>));
using Form form = editor.CreateCollectionForm();

dynamic a = form.TestAccessor.Dynamic;
a.AddItems(new object[] { 1, 2, 3 });

@LeafShi1 LeafShi1 Jun 24, 2026

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Suggestion: The test implicitly assumes AddItems selects the last added item (index 2). If AddItems behavior changes in the future, this test will fail without a clear reason.

Consider adding an explicit assertion on the initial state:

a.AddItems(new object[] { 1, 2, 3 });

// AddItems selects the last added item by default
listBox.SelectedIndex.Should().Be(2);
up.Enabled.Should().BeTrue();
down.Enabled.Should().BeFalse();


ListBox listBox = (ListBox)a._listBox;
Button up = (Button)a._upButton;
Button down = (Button)a._downButton;

up.Enabled.Should().BeTrue();
down.Enabled.Should().BeFalse();

listBox.SelectedIndex = 0;
up.Enabled.Should().BeFalse();
down.Enabled.Should().BeTrue();

@LeafShi1 LeafShi1 Jun 24, 2026

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Suggestion: This test relies on the SelectedIndexChanged event being wired up to call UpdateEnabled() automatically. In a test environment (where the form is never shown), the event wiring may not be fully initialized, making this test fragile.

Consider calling UpdateEnabled() explicitly after each selection change to make the test deterministic:

listBox.SelectedIndex = 0;
a.UpdateEnabled();  // Don't rely on event — call explicitly
up.Enabled.Should().BeFalse();

This also makes the test more readable — it's clear we're testing the logic of UpdateEnabled(), not the event wiring.

listBox.ClearSelected();
listBox.SelectedIndex = 1;
up.Enabled.Should().BeTrue();
down.Enabled.Should().BeTrue();

listBox.ClearSelected();
up.Enabled.Should().BeFalse();
down.Enabled.Should().BeFalse();

listBox.Items.Clear();

@LeafShi1 LeafShi1 Jun 24, 2026

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Suggestion: After listBox.Items.Clear(), SelectedIndex becomes -1. If UpdateEnabled() is not triggered by the clear operation, the button states here could be stale values from the previous assertions rather than reflecting the current state.

Same recommendation: call a.UpdateEnabled() explicitly after AddItems to ensure we're verifying the actual logic, not leftover state.

a.AddItems(new object[] { 42 });
up.Enabled.Should().BeFalse();
down.Enabled.Should().BeFalse();
}

[Theory]
[InlineData(typeof(object), typeof(object))]
[InlineData(typeof(string), typeof(object))]
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