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wpf-HwndHost-child-hwnd-correct-size-during-DPI-changes.md

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HwndHost now correctly resizes child-HWND during DPI changes

Scope

Major

Version Introduced

4.8

Source Analyzer Status

NotPlanned

Change Description

In .NET Framework 4.7.2 and earlier versions, when WPF was run in Per-Monitor Aware mode, controls hosted within xref:System.Windows.Interop.HwndHost were not sized correctly after DPI changes, such as when moving applications from one monitor to another. This fix ensures that hosted controls are sized appropriately.

  • Quirked
  • Build-time break

Recommended Action

In order for the application to benefit from these changes, it must run on the .NET Framework 4.7.2 or later, and it must opt-in to this behavior by setting the following AppContext Switch in the <runtime> section of the app config file to false, as the following example shows.

    <?xml version="1.0" encoding="utf-8"?>
    <configuration>
      <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7"/>
      </startup>
      <runtime>
        <!-- AppContextSwitchOverrides value attribute is in the form of 'key1=true|false;key2=true|false  -->
        <AppContextSwitchOverrides value="Switch.System.Windows.DoNotUsePresentationDpiCapabilityTier2OrGreater=false" />
      </runtime>
    </configuration>

Category

WPF