Combobox popup width changes with variable Combobox item sizes

Describe the bug When the combo box items are different sizes, the popup changes it’s width while scrolling wich makes it quite unusable.

To Reproduce Create a combo that forces to display a scroll, width of different item sizes:

  <ComboBox SelectedIndex="0">
    <ComboBoxItem>Example Item 01</ComboBoxItem>
    <ComboBoxItem>Example Item 02</ComboBoxItem>
    ... etc ...
    <ComboBoxItem>Very very very very very very very long item</ComboBoxItem>
    <ComboBoxItem>Example Item 25</ComboBoxItem>
    <ComboBoxItem>Example Item 26</ComboBoxItem>
    ... etc ...
  </ComboBox>

Expected behavior The width of the popup should be the max width of the longest item in the combo.

Desktop (please complete the following information):

• OS: Windows
• Version master latest.

[maxkatz6]

Yes

[maxkatz6]

Well, the reason I reported this, is because it was working as expected in 0.10.x and the default panel for ComboBox was already a VirtualizingStackPanel.

In 0.10 ComboBox wasn’t virtualized by default. So it makes sense that it worked before. Now, there is no context information for the combobox to know possible width of unrealized items.