Microsoft.Maui.IPropertyMapper - The type '' cannot be used as a type parameter... There is no implicit conversion

user_1662619 0
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I'm trying to get maps to work on .net MAUI and found this blog post (linked to from the official MAUI blog). https://www.cayas.de/blog/dotnet-maui-custom-map-handler I've downloaded the repo linked at the end of the blog but I can't get it to run.

In the blog post the MapHandler code looks like this:

public static IPropertyMapper<IMap, MapHandler> MapMapper = new PropertyMapper<IMap, MapHandler>(ViewMapper)
    {  };

But in the repo it looks like this:

public static IPropertyMapper<MapView, MapHandler> MapMapper = new PropertyMapper<MapView, MapHandler>(ViewMapper)
        { };

Neither of which work for me, as I get the error (at runtime) below.

The type 'MapControlDemo.Handlers.MapHandler' cannot be used as type parameter 'TViewHandler' in the generic type or method 'PropertyMapper<TVirtualView, TViewHandler>'. There is no implicit reference conversion from 'MapControlDemo.Handlers.MapHandler' to 'Microsoft.Maui.IElementHandler'

Confusingly there are another couple of errors that shouldn't be errors?? Other errors

Any ideas? I contacted the author and he suggested it could be my maui version as it works for him, but I'm on the latest.

.net-maui maui
1 Answers

Perhaps the author was building on a Mac.

I've confirmed that an attempt to build on Windows results in a build error. VS Version 17.3.0 Preview 1.1
The error I got was

Error   CS0311  The type 'MapControlDemo.Handlers.MapHandler' cannot be used
 as type parameter 'TViewHandler'
 in the generic type or method 'IPropertyMapper<TVirtualView, TViewHandler>'.
 There is no implicit reference conversion from
 'MapControlDemo.Handlers.MapHandler' to
 'Microsoft.Maui.IElementHandler'.
    MapControlDemo (net6.0-android) C:\...\maui-maps\Handlers\MapHandler.cs 6

HOWEVER, I was able to RUN on Android - by selected an Android emulator as target (so using net6.0-android) and pressing F5 - therefore that error is misleading.

Given that this is only implemented on iOS and Android, I recommend editing .csproj to REMOVE Windows platform. I also removed MacCatalyst (maybe that would work but I was going for simplest test):
Change:

        <TargetFrameworks>net6.0-android;net6.0-ios;net6.0-maccatalyst</TargetFrameworks>
        <TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('windows'))">$(TargetFrameworks);net6.0-windows10.0.19041.0</TargetFrameworks>

To:

        <TargetFrameworks>net6.0-android;net6.0-ios</TargetFrameworks>

Then I was able to build.

NOTE: Without adding a Google Maps ID, when ran on Android, the result was an empty map.

tl;dr Easiest way to test is on a Mac, targetting iOS.

user_1993640
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