Maui tells me I have a problem but surely it could narrow it down

WillAutioItrax 201

In my Maui app, I get the message:

[0:] Microsoft.Maui.Controls.Element: Warning: Microsoft.Maui.Controls.Label is already a child of Microsoft.Maui.Controls.Grid. Remove Microsoft.Maui.Controls.Label from Microsoft.Maui.Controls.Grid before adding to Microsoft.Maui.Controls.Grid.

Java.Lang.IllegalStateException: 'The specified child already has a parent. You must call removeView() on the child's parent first.'

If the compiler can tell me there is a problem with a Grid and a Label, surely it can tell me the name of the Grid and the Label, or a line number or something to help me find the source of the problem. I think this is a bug in the compiler - a serious short coming.

How else can I find the Grid and Label responsible for this issue?

Thanks

Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 35,831 Reputation points Microsoft Vendor

2023-09-06T06:46:35.8333333+00:00

You get this error when you run the app on Android platform, right? I saw there is fixed issue related to setting VerticalOptions="CenterAndExpand" for the Label. What's the detailed MAUI version and VS version? Could you please identify which page is having the problem while loading and share some code snippets so that I can reproduce the issue?

Will Autio 5

@Wenyan Zhang Thanks for taking an interest in this issue.

I am upgrading our XF app to Maui and initially just testing/running it on Android.

I am using VS 17.7.3 and net7.0

The answer to the rest of your questions is ... complicated.

This part of the app consists of a CustomTabbedPage with 5 tabs. Two of the tabs are of interest. The one tab is the one we enter on (we have to start somewhere). The other is the one that I tap on and when all is said and done, something causes an exception. Let's call this the ActivePage.

The ActivePage consists of some XAML for Labels, Buttons, Pickers and finally this layout:

<StackLayout

<StackLayout

    <ScrollView

        StackLayout

            <local:ExtendedExpander      // a SyncFusion Control

The expander gets populated programatically and consists of about 10 groups where the Group name appears on the Expander and when clicked on, the related Labels, Checkboxes and Pickers get displayed (all added programatically). And this all worked in XF.

Now, as far as I can tell, something in Android goes horribly wrong and I get 100 lines of Android StackTrace that starts with:

[InputTransport] Input channel destroyed: 'ClientS', fd=120

[0:] Microsoft.Maui.FontManager: Warning: Unable to load font '/data/user/0/com.itraxonline.i_traxmobile/cache/Maui Material Assets.ttf' from assets.

Java.Lang.RuntimeException: Font asset not found /data/user/0/com.itraxonline.i_traxmobile/cache/Maui Material Assets.ttf

...

and ends with:

	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)
[0:] Microsoft.Maui.Controls.Element: Warning: Microsoft.Maui.Controls.Label is already a child of Microsoft.Maui.Controls.Grid. Remove Microsoft.Maui.Controls.Label from Microsoft.Maui.Controls.Grid before adding to Microsoft.Maui.Controls.Grid.
**Java.Lang.IllegalStateException:** 'The specified child already has a parent. You must call removeView() on the child's parent first.'

Two things:
1) So far I have not found any references to 
2) On the ActivePage I do not use a Grid anywhere.

Previously I asked a question about the font at this site:
https://learn.microsoft.com/en-us/answers/questions/1341119/in-maui-code-i-am-getting-a-missing-font-message-b

And after some back and forth, received the recommendation to call Microsoft Support. 

Later I started looking at the Grid and Label issue (which is really only a Warning, well Maui calls it a Warning and on the next line it starts with 
**Java.Lang.IllegalStateException:**

So, is it a Warning or an Exception? (Rhetorical question). VS displays a popup window that looks like this:
Exception Unhandled
**Java.Lang.IllegalStateException:** 'The specified child already has a parent. You must call removeView() on the child's parent first.'

So, I guess the Exception wins.

Again, thanks for having a look at this.
Best Regards,
Will

Will Autio 5 Reputation points

2023-09-07T02:00:24.21+00:00
@Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.)

Argh! I tried adding a comment and it disappeared so I'll try again. Thankfully I made a copy.

Thanks for taking an interest in this issue.

I am upgrading our XF app to Maui and initially just testing/running it on Android.

I am using VS 17.7.3 and net7.0

The answer to the rest of your questions is ... complicated. Which is why I thought about creating a sample program but was not sure that at the end of the exercise it would break in the same way. Please read on...

This part of the app consists of a CustomTabbedPage with 5 tabs. Two of the tabs are of interest. The one tab is the one we enter on (we have to start somewhere). The other is the one that I tap on and when all is said and done, something causes an exception. Let's call this the ActivePage.

The ActivePage consists of some XAML for Labels, Buttons, Pickers and finally this layout:

<StackLayout

<StackLayout <ScrollView StackLayout <local:ExtendedExpander // a SyncFusion Control

The expander gets populated programatically and consists of about 10 groups where the Group name appears on the Expander and when clicked on, the related Labels, Checkboxes and Pickers get displayed (all added programatically). And this all worked in XF.

Now, as far as I can tell, something in Android goes horribly wrong and I get 100 lines of Android StackTrace that starts with:

[InputTransport] Input channel destroyed: 'ClientS', fd=120

[0:] Microsoft.Maui.FontManager: Warning: Unable to load font '/data/user/0/com.itraxonline.i_traxmobile/cache/Maui Material Assets.ttf' from assets.

Java.Lang.RuntimeException: Font asset not found /data/user/0/com.itraxonline.i_traxmobile/cache/Maui Material Assets.ttf

...

and ends with:

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)

[0:] Microsoft.Maui.Controls.Element: Warning: Microsoft.Maui.Controls.Label is already a child of Microsoft.Maui.Controls.Grid. Remove Microsoft.Maui.Controls.Label from Microsoft.Maui.Controls.Grid before adding to Microsoft.Maui.Controls.Grid.

Java.Lang.IllegalStateException: 'The specified child already has a parent. You must call removeView() on the child's parent first.'

Two things:

So far I have not found any references to Maui Material Assets.ttf anywhere.

On the ActivePage I do not use a Grid anywhere.

Previously I asked a question about the font at this site:

https://learn.microsoft.com/en-us/answers/questions/1341119/in-maui-code-i-am-getting-a-missing-font-message-b

And after some back and forth, received the recommendation to call Microsoft Support.

Later I started looking at the Grid and Label issue (which is really only a Warning, well Maui calls it a Warning and on the next line it starts with

Java.Lang.IllegalStateException:

So, is it a Warning or an Exception? (Rhetorical question). VS displays a popup window that looks like this:

Exception Unhandled

Java.Lang.IllegalStateException: 'The specified child already has a parent. You must call removeView() on the child's parent first.'

So, I guess the Exception wins. So, maybe they are related issues and I should call MS Support.

Again, thanks for having a look at this.

Best Regards,

Will
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 35,831 Reputation points Microsoft Vendor

2023-09-11T06:51:55.2+00:00

Sorry for the late response, I didn't see the message before.

You mean you got the warnings in ActivePage, but there is not a grid in this page, right? You could try to remove the <local:ExtendedExpander, then check if the issue is related to this control.

For the font issue, it's recommended that you connect the 1:1 support for further help. Thanks for your understanding and collaboration.

1 answer

Bill Fulton 6 Reputation points

2025-02-20T02:37:45.22+00:00

I get this quite infuriating error a lot in converting a Xamarin app. Typically the exception is not raised until the UI is updated, but the problem actually happened much earlier and somehow had been 'remembered' by MAUI meanwhile! An example is a static list of visual elements that is added to a StackLayout on multiple occasions. The parent of each visual element must then be removed before adding the visual element. Can be tedious to find, in a complex app.
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Maui tells me I have a problem but surely it could narrow it down

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