[Bug] [Expander] InvalidOperationException: Header not initialized

[kevin68]

Description

Since updating from XCT 1.0.3 to 1.1.0 the application throws an exception when displaying the main page that contains an Expander.
I found out that the crash happens when I set the property Direction to a value other than Down and whether or not I define a Header. After some digging it seems to come from this line which was added by this commit.

Exception: System.InvalidOperationException: Header not initialized.

Stacktrace (not much)

[mono] System.InvalidOperationException: Header not initialized
[mono]   at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.7(intptr,intptr,intptr)
[mono]   at (wrapper native-to-managed) Android.Runtime.DynamicMethodNameCounter.7(intptr,intptr,intptr)

Steps to Reproduce

1. Create a blank Xamarin.Forms project
2. Install the Xamarin Community Toolkit 1.1.0
3. Add xmlns:xct="http://xamarin.com/schemas/2020/toolkit" to the main page
4. Add a simple Expander with a Direction in the content of the main page

       <xct:Expander Direction="Right">
            <xct:Expander.Header>
                <Label Text="header"/>
            </xct:Expander.Header>
            <Label Text="content"/>
        </xct:Expander>

5. Launch the app

Expected Behavior

The main page displays with the Expander

Actual Behavior

Visual studio catch an unhandled exception

Basic Information

• Version with issue: 1.1.0
• Last known good version: 1.0.3
• IDE: Visual Studio 2019 16.9.2
• Platform Target Frameworks:
  • iOS: 11.4
  • Android: 11.0
• Android Support Library Version: None
• Nuget Packages:
  • Xamarin.Essentials@1.6.1
  • NETStandard.Library@2.0.3
  • Xamarin.Forms@5.0.0.2012
• Affected Devices:
  • Pixel 3XL (Android 11.0)
  • Pixel 3a (Emulator, Android 9.0)
  • IPhone SE (iOS 14.4)

Workaround

Set the direction to Down, then change it after InitializeComponent() is called.

Reproduction imagery

N/A

Reproduction Link

Repro project (489ko)

[AndreiMisiukevich]

Should be
void SetHeader(View? oldHeader)

And the line you mentioned should be dropped.

Great report!