Fix FlatStyle drawing of ComboBox #6505
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RussKie
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Fixes #6494
Proposed changes
ComboBox.FlatComboAdapter.ValidateOwnerDrawRegionscontained a bug in its initial null check that prevented the method from executing. This bug existed under Framework 4.8 (and possibly quite earlier):https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/ComboBox.cs,6102
The bug was fixed in #6300, which resulted in a regression when drawing a
ComboBoxwithFlatStyle.FlatorFlatStyle.Popup.While the stated purpose of
ValidateOwnerDrawRegionswas to reduce screen flicker, the fact remains that the method never actually executed and allowing it to execute now is causing problems. This PR fixes the issue by just removing the method altogether.Customer Impact
ComboBoxwill draw itself correctly again.Regression?
Risk
Screenshots
Before
Reference #6494 to see example of issue prior to fix
After
Screenshot taken after removal of
ValidateOwnerDrawRegionsTest methodology
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