"dynamic" data type is recognized as "object" when using Excel COM

[JohnyL]

I have the following simple code which defines last cell with non-empty data, defines its row and gets its value:

using Excel = Microsoft.Office.Interop.Excel;

Excel.Application xlApp = new Excel.Application { Visible = true };
Excel.Workbook xlBook = xlApp.Workbooks[1];
Excel.Worksheet sheet = xlBook.Sheets[1] as Excel.Worksheet;
int lastRow = sheet.Cells[sheet.Rows.Count, "Q"].End[Excel.XlDirection.xlUp].Row;
dynamic value = sheet.Cells[lastRow, "Q"].Value;

When I'm building the project using .NET 5 (5.0.101 or 5.0.200-preview.20601.7 SDK), I get the following two errors in Output window:

error CS1061: 'object' does not contain a definition for 'End' and no accessible extension method 'End' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)

error CS1061: 'object' does not contain a definition for 'Value' and no accessible extension method 'Value' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)

Here are problems:

1. When I'm using .NET Framework 4.8, the project is built fine without any errors and code executes perfectly. In .NET 5, however, the dynamic data type is somehow recognized as object.
2. I emphasized "in Output window", because now errors do not show up in "Error List" anymore - they are now seen in "Output" window. For instance, if I remove last semicolon in my code, no errors appear in "Error List". Instead, I should build project first, and only then error appears, but in "Output" window rather than "Error List" window.

Visual Studio Version: 16.9.0 Preview 2.0

[tmeschter]

Hi @JohnyL,

What version of Visual Studio are you using? You can get this from the "Help | About Microsoft Visual Studio" menu item, and it will be something like "Version 16.9.0 Preview 3.0 [30808.111.main]".

Also, can you show us the COMReferences in your project file (or better yet, attach the whole file)?

[JohnyL]

@tmeschter I'm using 16.9.0 Preview 2.0 (btw, it's strange but VS installer does not offer Preview 3.0 - I just don't see it).
The whole project file:

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>WinExe</OutputType>
	    <TargetFramework>net5.0-windows</TargetFramework>
	    <UseWPF>true</UseWPF>
	    <NoWin32Manifest>true</NoWin32Manifest>
    </PropertyGroup>

    <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
        <PlatformTarget>x64</PlatformTarget>
    </PropertyGroup>

    <ItemGroup>
        <COMReference Include="Microsoft.Office.Excel">
            <WrapperTool>primary</WrapperTool>
            <VersionMinor>9</VersionMinor>
            <VersionMajor>1</VersionMajor>
            <Guid>00020813-0000-0000-c000-000000000046</Guid>
            <Lcid>0</Lcid>
            <Isolated>false</Isolated>
            <EmbedInteropTypes>true</EmbedInteropTypes>
        </COMReference>
    </ItemGroup>

</Project>

[tmeschter]

Do you see these errors if you build from a developer command prompt via "msbuild Foo.proj", or only when you build in VS?

[JohnyL]

@tmeschter Yes, same two errors via msbuild.

[tmeschter]

OK, then that is going to be an issue with a lower-level component than the project system. I'm transferring this issue to dotnet/sdk.

[JohnyL]

Any news on this? I still get this error in VS 16.9.0 Preview 4.0. It's impossible to work. Moreover, this error doesn't appear in Error List.

[JohnyL]

I would like to add that this does not happen in console app, but does happen in WPF or WinForms app. Also same thing happens in .NET Core 3.1.

[jaredpar]

When I'm using .NET Framework 4.8, the project is built fine without any errors and code executes perfectly. In .NET 5, however, the dynamic data type is somehow recognized as object.

This behavior indicates that on .NET Framework the COM reference is being passed via /link while in .NET 5 it's being passed via /reference. The reason is that when passed via /link the C# compiler will treat method / property return types that are object as if they were dynamic (docs). Hence it's almost certain that in the .NET 5 case your COM library is being built with /reference when it should be /link

This is generally controlled via the <EmbedInteropTypes> property. If it's true then it will be treated as /link.

The whole project file:

I tried this locally and added a global.json to ensure I was using the 5.0.103 SDK and could not reproduce the problem. I confirmed in my binlog that the Excel reference is being passed correctly

Can you try getting a binlog for your failed build and posting it somewhere that can be examined?

[jaredpar]

@terrajobst helpfully figured out what I was missing and created a repro. The part I was missing is that it needs to be a WPF project. In that case the reference is not passed as EmbedInteropTypes.

Moving to the WPF repo for triage.

[JohnyL]

@jaredpar I have already pointed out that this doesn't happen in console, but in WPF or WinForms.

[jaredpar]

@JohnyL yes but you also provided a sample project file for console apps, hence that's what I used when attempting to repro.

[ryalanms]

Thank you @JohnyL and @jaredpar for the report and investigation. Capitalizing the 'T' worked for me locally.

    <ItemGroup>
             ...
            <EmbedInteropTypes>True</EmbedInteropTypes>
        </COMReference>
    </ItemGroup>