Add Maui default global usings in SDK targets

[mhutch]

Following the pattern in dotnet/sdk#18459, we should add default global usings for Maui in the SDK targets and the corresponding MSBuild property to disable them.

[Redth]

@jonathanpeppers are you able to assist on this?

For MAUI I think we need:

using Microsoft.Maui;
using Microsoft.Maui.Graphics;
using Microsoft.Maui.Controls;

The last one (Controls) maybe is worth debating...

[jonathanpeppers]

I don't think the changes in dotnet/sdk have landed yet, but we can try it soon, I think?

You will be able to put this in a .targets file:

<ItemGroup>
  <Import Include="Microsoft.Maui" />
  <Import Include="Microsoft.Maui.Controls" />
</ItemGroup>

Let me do the Android side first, and I'll know how it works: dotnet/android#6075

[Clancey]

Right now, if you are trying to use something like Comet, and you have using Microsoft.Maui.Controls as well, it will cause a lot of confusion. Since using Microsoft.Maui.Controls.Button and Comet.Button

[Redth]

@Clancey yeah that's what I was thinking too. Perhaps we should leave controls out then, or better yet we can conditionally put that one in the item group if the controls stuff is referenced?

@jonathanpeppers did we ever make a property to exclude Maui controls references explicitly? Do we need one and put this behind it as well?

[jonathanpeppers]

Yes, each global using could be split up across parts of Maui where it makes sense. I don’t think you have an explicit thing to exclude Controls, but UseMauiCore, UseMauiAssets, and UseMauiEssentials (and not UseMaui) would exclude Controls.

[saint4eva]

@jonathanpeppers are you able to assist on this?

For MAUI I think we need:

using Microsoft.Maui;
using Microsoft.Maui.Graphics;
using Microsoft.Maui.Controls;

The last one (Controls) maybe is worth debating...

The last one (Controls) should not be included by default since there are other app models such as Comet, Fabolous and Reactive UI

[mhutch]

So using the relationships defined in f82db03 (UseMaui sets UseMauiCore and _UseMauiControls) it would look something like this?

<PropertyGroup Condition="'$(DisableImplicitNamespaceImports_Maui)' != 'true'">
  <Import Include="Microsoft.Maui" Condition="'$(UseMauiCore)'=='true'" />
  <Import Include="Microsoft.Maui.Graphics" Condition="'$(UseMauiCore)'=='true'" />
  <Import Include="Microsoft.Maui.Controls" Condition="'$(_UseMauiControls)'=='true'" />
</PropertyGroup>

[jonathanpeppers]

@mhutch that looks right to me.

[mhutch]

The Maui template's Startup.cs has the following usings:

using Microsoft.Maui;
using Microsoft.Maui.Hosting;
using Microsoft.Maui.Controls.Compatibility;
using Microsoft.Maui.Controls.Hosting;
using Microsoft.Maui.Controls.Xaml;

And default usings will only get rid of one of these. Should we be adding more of them?

For reference, here's what the base and web SDKs add: dotnet/sdk#18825 (comment). Note that web does include its .Hosting namespace.

[Clancey]

using Microsoft.Maui.Hosting; is only used in Startup. The rest are for Controls only. They would cause issues if in Comet.

[mhutch]

Sure, but the hosting one would be consistent with web, and the rest would be conditioned on $(_UseMauiControls)

[saint4eva]

The Maui template's Startup.cs has the following usings:

using Microsoft.Maui;
using Microsoft.Maui.Hosting;
using Microsoft.Maui.Controls.Compatibility;
using Microsoft.Maui.Controls.Hosting;
using Microsoft.Maui.Controls.Xaml;

And default usings will only get rid of one of these. Should we be adding more of them?

For reference, here's what the base and web SDKs add: dotnet/sdk#18825 (comment). Note that web does include its .Hosting namespace.

Hmmm Xaml? Remember other app mdels such as Comet and Fabulous. Thank you.