.NET 4.8 WPF UseLegacyAccessibilityFeatures: Application Crash

[rockerinthelocker]

Setting Switch.UseLegacyAccessibilityFeatures, Switch.UseLegacyAccessibilityFeatures.2, and Switch.UseLegacyAccessibilityFeatures.3 (or any other valid combination) to true causes the application to crash on start.

Additionally, related exception messages make no sense at all.

There is no workaround available.

First opened here: microsoft/dotnet#1064

[ryalanms]

Thanks, @rockerinthelocker. Do you have a minimal repro for this issue?

[rockerinthelocker]

Sure thing, @ryalanms.

The issue is reproduceable by creating a default WPF desktop (.NET) project in Visual Studio using the <AppContextSwitchOverrides> settings as shown below in the App.config file.

As noted at https://github.com/dotnet/docs/blob/main/docs/framework/whats-new/whats-new-in-accessibility.md#restoring-legacy-behavior and https://docs.microsoft.com/en-us/dotnet/framework/migration-guide/retargeting/4.7-4.8#suggestion, setting these switches to true should restore the legacy behavior of previous .NET versions.

However, as mentioned above, the application will crash and error messages make no sense, especially those returned when setting UseLegacyAccessibilityFeatures.3 and UseLegacyAccessibilityFeatures.4 switches to true since the UseLegacyToolTipDisplay is not set at all.

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

System.NotSupportedException
HResult=0x80131515
Message=Desktop applications are required to opt in to all earlier accessibility improvements to get the later improvements. To do this, ensure that if the AppContext switch 'Switch.UseLegacyAccessibilityFeatures.N' is set to 'false', then 'Switch.UseLegacyAccessibilityFeatures' and all 'Switch.UseLegacyAccessibilityFeatures.M' switches, when M < N, evaluate to false as well. Note that, if a switch for a particular set of accessibility improvements is not present, its value is determined by the target framework version. You can remedy this by adding these switches and setting their value to false.
Source=WindowsBase
StackTrace:
...

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />
    </startup>
    <runtime>
        <!-- AppContextSwitchOverrides value attribute is in the form of 'key1=true|false;key2=true|false  -->
        <AppContextSwitchOverrides value="Switch.UseLegacyAccessibilityFeatures=true;Switch.UseLegacyAccessibilityFeatures.2=true" />
    </runtime>
</configuration>

System.NotSupportedException
HResult=0x80131515
Message=Desktop applications are required to opt in to all earlier accessibility improvements to get the later improvements. To do this, ensure that if the AppContext switch 'Switch.UseLegacyAccessibilityFeatures.N' is set to 'false', then 'Switch.UseLegacyAccessibilityFeatures' and all 'Switch.UseLegacyAccessibilityFeatures.M' switches, when M < N, evaluate to false as well. Note that, if a switch for a particular set of accessibility improvements is not present, its value is determined by the target framework version. You can remedy this by adding these switches and setting their value to false.
Source=WindowsBase
StackTrace:
...

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />
    </startup>
    <runtime>
        <!-- AppContextSwitchOverrides value attribute is in the form of 'key1=true|false;key2=true|false  -->
        <AppContextSwitchOverrides value="Switch.UseLegacyAccessibilityFeatures=true;Switch.UseLegacyAccessibilityFeatures.2=true;Switch.UseLegacyAccessibilityFeatures.3=true" />
    </runtime>
</configuration>

System.NotSupportedException
HResult=0x80131515
Message=Desktop applications setting AppContext switch 'Switch.UseLegacyToolTipDisplay' to false are required to opt in to all earlier accessibility improvements. To do this, ensure that the AppContext switch 'Switch.UseLegacyAccessibilityFeatures.3' is set to 'false', then 'Switch.UseLegacyAccessibilityFeatures' and all 'Switch.UseLegacyAccessibilityFeatures.M' switches, when M < 3, evaluate to false as well. Note that, if a switch for a particular set of accessibility improvements is not present, its value is determined by the target framework version. You can remedy this by adding these switches and setting their value to false.
Source=WindowsBase
StackTrace:
...

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />
    </startup>
    <runtime>
        <!-- AppContextSwitchOverrides value attribute is in the form of 'key1=true|false;key2=true|false  -->
        <AppContextSwitchOverrides value="Switch.UseLegacyAccessibilityFeatures=true;Switch.UseLegacyAccessibilityFeatures.2=true;Switch.UseLegacyAccessibilityFeatures.3=true;Switch.UseLegacyAccessibilityFeatures.4=true" />
    </runtime>
</configuration>

System.NotSupportedException
HResult=0x80131515
Message=Desktop applications setting AppContext switch 'Switch.UseLegacyToolTipDisplay' to false are required to opt in to all earlier accessibility improvements. To do this, ensure that the AppContext switch 'Switch.UseLegacyAccessibilityFeatures.3' is set to 'false', then 'Switch.UseLegacyAccessibilityFeatures' and all 'Switch.UseLegacyAccessibilityFeatures.M' switches, when M < 3, evaluate to false as well. Note that, if a switch for a particular set of accessibility improvements is not present, its value is determined by the target framework version. You can remedy this by adding these switches and setting their value to false.
Source=WindowsBase
StackTrace:
...