How do I use Xamarin Shell in C# code?

Question

How do I use Xamarin Shell in C# code?

EasyGoingPat 261

I am having terrible difficulty getting anywhere with the new Shell because I am wanting to do it in C# code if possible and every single example seems to use XAML.

Can anyone point me at an example piece of code that uses the Shell?

Patrick

JarvanZhang 23,971

Hi, PatrickRyder. To create a basic shell application in code, first initialize the FlyoutItem or Tabbar and add the pages. Then add the flyout items to Shell.Items. Please check the code.

public class CustomShell : Shell
{
    public CustomShell()
    {

        var flyoutItem1 = new FlyoutItem
        {
            Title = "Item_1"
        };
        flyoutItem.Items.Add(new ShellContent { Content = new Page1(), Title = "page1" });
        flyoutItem.Items.Add(new ShellContent { Content = new Page2(), Title = "page2" });

        var flyoutItem2 = new FlyoutItem
        {
            Title = "Item_2"
        };
        ...

        this.Items.Add(flyoutItem1);
        this.Items.Add(flyoutItem2);
    }
}

EasyGoingPat 261 Reputation points

2021-03-31T07:16:31.23+00:00
Thank you for the answer.

Unfortunately, the code doesn't compile for me. There is no flyoutItem reference.

I am wanting to use a Tab Bar as my main screen. Could you post code to set-up a basic one of those?

Also, at the moment, I am doing something very similar to your code:

public class AppShell : Shell { public AppShell() { ShellContent content = new ShellContent() { ContentTemplate = new DataTemplate( typeof(HomeView) ) }; Items.Add( content ); } }

When I do this, I get the following warning:

[TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window). This may cause bugs by forcing views inside the table view to load and perform layout without accurate information... (TRUNCATED)

Do you have any idea what might be causing this?

JarvanZhang 23,971

What is the 'HomeView'? Is it a contentPage? I tested the code on my side, it works fine.

public class CustomShell : Shell
{
    public CustomShell()
    {
        ShellContent content1 = new ShellContent()
        {
            ContentTemplate = new DataTemplate(typeof(MainPage))
        };
        Items.Add(content);
    }
}

EasyGoingPat 261 Reputation points

2021-03-31T10:55:07.907+00:00

My inheritance is HomeView - ViewBase - ContentPage.

Are you saying you run my code and don't see the same warning that I am seeing?
JarvanZhang 23,971 Reputation points

2021-03-31T11:39:41.547+00:00

Yes, it works fine on my side. This may be a illustrates warning, did that effect the deploy? What's the version of the VS and XCode? Try to update both to lastest stable version and test again.
EasyGoingPat 261 Reputation points

2021-04-01T08:37:04.697+00:00
@JarvanZhang

VS is 16.9.3. XCode is 14.4.

It seems this warning has been seen by a number of people: https://stackoverflow.com/questions/57897288/uitableviewalertforlayoutoutsideviewhierarchy-error-warning-once-only-ios-13-g

Some say it is harmless but I'm not comfortable with leaving a warning I don't even understand the cause of. And my Xamarin/iOS knowledge is not up to investigating this more deeply, certainly not in a practical amount of time.

It also worries me that you can run my code and see no problem.

So I guess I am stuck with trying to get the old stack-based navigation to do what I need.

Patrick
JarvanZhang 23,971 Reputation points

2021-04-01T13:56:50.38+00:00

Hi, PatrickRyder. Did you face the warning in other projects? And will the warning occur if you create a shell template application directly?
EasyGoingPat 261 Reputation points

2021-04-19T07:16:56.91+00:00

@JarvanZhang

I have just created a brand new Xamarin iOS project, using the Shell Navigation Tabbed template and I do see exactly the same warning.

So maybe the people who say this is harmless are correct. I would still like to know why it happens though. And I have the problem that we have a policy of zero warnings in production code.

Kind wishes - Patrick
EasyGoingPat 261 Reputation points

2021-04-20T06:47:50.367+00:00
@JarvanZhang

I'm confused! Isn't that what I am doing here?

Patrick
JarvanZhang 23,971 Reputation points

2021-04-20T14:53:27.33+00:00

Hi, PatrickRyder. There is nothing wrong with the code and the project is deployed well, the illustrates warning is due to Visual Studio or the iOS native.
EasyGoingPat 261 Reputation points

2021-04-21T06:37:15.053+00:00
Hi, @JarvanZhang

That's reassuring to know. If I did want to report this as a bug, though, how would I do this, as the feedback in Visual Studio brings me here?

Patrick
JarvanZhang 23,971 Reputation points

2021-04-22T08:32:49.823+00:00

Hi @EasyGoingPat , sorry for the miss-leading comment, we can reproduce the warning from Shell Navigation Tabbed template, the warning showed up in the output window when app run, it should be a runtime warning thrown from native iOS. This can be a bug from the template, it's suggested to report this to the Xamarin.Forms github repo and check if there's any workaround to get rid of this.

Your answer

JarvanZhang 23,971 Reputation points

2021-03-30T12:41:10.23+00:00

Hi, PatrickRyder. To create a basic shell application in code, first initialize the FlyoutItem or Tabbar and add the pages. Then add the flyout items to Shell.Items. Please check the code.

public class CustomShell : Shell { public CustomShell() { var flyoutItem1 = new FlyoutItem { Title = "Item_1" }; flyoutItem.Items.Add(new ShellContent { Content = new Page1(), Title = "page1" }); flyoutItem.Items.Add(new ShellContent { Content = new Page2(), Title = "page2" }); var flyoutItem2 = new FlyoutItem { Title = "Item_2" }; ... this.Items.Add(flyoutItem1); this.Items.Add(flyoutItem2); } }
EasyGoingPat 261 Reputation points

2021-03-31T07:16:31.23+00:00

Thank you for the answer.

Unfortunately, the code doesn't compile for me. There is no flyoutItem reference.

I am wanting to use a Tab Bar as my main screen. Could you post code to set-up a basic one of those?

Also, at the moment, I am doing something very similar to your code:

public class AppShell : Shell { public AppShell() { ShellContent content = new ShellContent() { ContentTemplate = new DataTemplate( typeof(HomeView) ) }; Items.Add( content ); } }

When I do this, I get the following warning:

[TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window). This may cause bugs by forcing views inside the table view to load and perform layout without accurate information... (TRUNCATED)

Do you have any idea what might be causing this?
JarvanZhang 23,971 Reputation points

2021-03-31T09:08:09.267+00:00

What is the 'HomeView'? Is it a contentPage? I tested the code on my side, it works fine.

public class CustomShell : Shell { public CustomShell() { ShellContent content1 = new ShellContent() { ContentTemplate = new DataTemplate(typeof(MainPage)) }; Items.Add(content); } }
EasyGoingPat 261 Reputation points

2021-03-31T10:55:07.907+00:00

My inheritance is HomeView - ViewBase - ContentPage.

Are you saying you run my code and don't see the same warning that I am seeing?
JarvanZhang 23,971 Reputation points

2021-03-31T11:39:41.547+00:00

Yes, it works fine on my side. This may be a illustrates warning, did that effect the deploy? What's the version of the VS and XCode? Try to update both to lastest stable version and test again.
EasyGoingPat 261 Reputation points

2021-04-01T08:37:04.697+00:00

@JarvanZhang

VS is 16.9.3. XCode is 14.4.

It seems this warning has been seen by a number of people: https://stackoverflow.com/questions/57897288/uitableviewalertforlayoutoutsideviewhierarchy-error-warning-once-only-ios-13-g

Some say it is harmless but I'm not comfortable with leaving a warning I don't even understand the cause of. And my Xamarin/iOS knowledge is not up to investigating this more deeply, certainly not in a practical amount of time.

It also worries me that you can run my code and see no problem.

So I guess I am stuck with trying to get the old stack-based navigation to do what I need.

Patrick
JarvanZhang 23,971 Reputation points

2021-04-01T13:56:50.38+00:00

Hi, PatrickRyder. Did you face the warning in other projects? And will the warning occur if you create a shell template application directly?
EasyGoingPat 261 Reputation points

2021-04-19T07:16:56.91+00:00

@JarvanZhang

I have just created a brand new Xamarin iOS project, using the Shell Navigation Tabbed template and I do see exactly the same warning.

So maybe the people who say this is harmless are correct. I would still like to know why it happens though. And I have the problem that we have a policy of zero warnings in production code.

Kind wishes - Patrick
EasyGoingPat 261 Reputation points

2021-04-20T06:47:50.367+00:00

@JarvanZhang

I'm confused! Isn't that what I am doing here?

Patrick
JarvanZhang 23,971 Reputation points

2021-04-20T14:53:27.33+00:00

Hi, PatrickRyder. There is nothing wrong with the code and the project is deployed well, the illustrates warning is due to Visual Studio or the iOS native.
EasyGoingPat 261 Reputation points

2021-04-21T06:37:15.053+00:00

Hi, @JarvanZhang

That's reassuring to know. If I did want to report this as a bug, though, how would I do this, as the feedback in Visual Studio brings me here?

Patrick
JarvanZhang 23,971 Reputation points

2021-04-22T08:32:49.823+00:00

Hi @EasyGoingPat , sorry for the miss-leading comment, we can reproduce the warning from Shell Navigation Tabbed template, the warning showed up in the output window when app run, it should be a runtime warning thrown from native iOS. This can be a bug from the template, it's suggested to report this to the Xamarin.Forms github repo and check if there's any workaround to get rid of this.

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How do I use Xamarin Shell in C# code?

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