ErrorBoundary support for multiple exceptions

[thirstyape]

Am I using this incorrectly? I implemented as per Documentation in MainLayout.razor with the slight change that in my <ErrorContent> section I added a button that triggers errorBoundary?.Recover();.

My test involved throwing a generic exception with a message from a child component in protected override void OnInitialized(). The result was that instead of displaying the content of @Body or the ErrorContent, there was nothing. Upon opening the browser inspector I had an empty <main></main>.

I also tried creating a custom class that implemented ErrorBoundary, but this did not help either.

Originally posted by @thirstyape in #30874 (comment)

[TanayParikh]

Does it work as expected if you throw the exception in OnParametersSet instead of OnInitialized? That's the event used in the docs and occurs after OnInitialized, so I wonder if this is an event ordering issue.

[ghost]

Hi @thirstyape. We have added the "Needs: Author Feedback" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[thirstyape]

Yes, it occurred in OnParametersSet as well. That was actually the first time I noticed this. I tested a basic scenario on Index.razor in its OnIntialized event and that worked as expected. Then I changed a different component from using OnIntialized to OnParametersSet which threw an exception (it should have). This caused the issue where there was nothing in the <main>. I then modified the event code to throw a generic exception instead of its normal actions, which caused the issue regardless of which event I used.

For reference, the component that is seeing issue is a Tab within a TabBar. A merge of the component tree has code similar to the following, I can provide more detailed samples if anything could use further investigation:

<MainLayout>
  <ErrorBoundary>
    <ChildContent>
       <UserPage>
          <TabBar>
            <Tab>
            </Tab>
            <Tab>
            </Tab>
          </TabBar>
       </UserPage>
    </ChildContent>
    <ErrorContent>
       <button @onclick="Reset">Reset Error</button>
    </ErrorContent>
  <ErrorBoundary>
</MainLayout>

The TabBar has <CascadingValue Value="this"> that contains the ChildContent for the Tab items. The Tab items add themselves to a collection in the TabBar in the event call.

[TanayParikh]

Could you please provide a minimal (using the base Blazor template with minimal additions) public github repro project to allow us to investigate further?

[ghost]

Hi @thirstyape. We have added the "Needs: Author Feedback" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[thirstyape]

Done, here is the repository.

Changes to default template:

• Add TabBar.razor and TabBar.razor.cs
• Add Tab.razor
• Update MainLayout.razor to include ErrorBoundary
• Update Index.razor to include TabBar
• Remove default error notice from index.html

Steps to reproduce:

1. Go into Tab.razor and change the OnInitialized to OnParametersSet
2. Run the app
3. Click the "Click me" text

This will produce some exceptions and the <article> will be empty. Interestingly, navigating to another component will correct the behavior and the Failed message appears.

Unexpected behavior:
I am not sure why, but when I started the app the Tab items did not appear. I needed to add the "Click me" tab directly in TabBar.razor and then click it to get the rest of the tabs to appear. After that they work as expected.

This is making me think the TabBar or Tab components may not be structured correctly.

[TanayParikh]

Thanks @thirstyape for the repro. I took a look and I believe it may be because in your example multiple exceptions are being thrown. If we update your example to just throw a single exception, things work as expected (Failed is shown).

diff --git a/BlazorApp1/Shared/Tab.razor b/BlazorApp1/Shared/Tab.razor
index f59c9e1..475e711 100644
--- a/BlazorApp1/Shared/Tab.razor
+++ b/BlazorApp1/Shared/Tab.razor
@@ -16,8 +16,8 @@
     [CascadingParameter]
     private TabBar Parent { get; set; }
 
-    protected override void OnInitialized()
-    //protected override void OnParametersSet() // Changing to this will cause the issue
+    // protected override void OnInitialized()^M
+    protected override void OnParametersSet() // Changing to this will cause the issue^M
     {
         Parent.Tabs.Add(Name, Icon);
     }
diff --git a/BlazorApp1/Shared/TabBar.razor.cs b/BlazorApp1/Shared/TabBar.razor.cs
index 24a6221..576ae92 100644
--- a/BlazorApp1/Shared/TabBar.razor.cs
+++ b/BlazorApp1/Shared/TabBar.razor.cs
@@ -39,8 +39,7 @@ public partial class TabBar
 
     private void OnTabBarChanged(string tab)
     {
-        Active = tab;
-        StateHasChanged();
+               throw new Exception("Yay for exceptions");^M
     }

This is making me think the TabBar or Tab components may not be structured correctly.

I believe this may be the case as well, I skimmed your code, but didn't immediately see what you were using to trigger the exception. My interpretation is the OnParametersSet is being triggered multiple times and that's causing a duplicate key to be added to the Parent.Tabs leading to the (multiple) exceptions. I'd recommend reviewing your code in that case. If you still believe this to be a framework bug, we'll need an even simpler repro app that doesn't require understanding the heuristics of TabBar, Tab, etc.

may be because in your example multiple exceptions are being thrown

@SteveSandersonMS are there any restrictions with respect to ErrorBoundary's and multiple exceptions?

[thirstyape]

Hi @TanayParikh, thank you for reviewing this.

Yes, as the <Tab> component has multiple instances, there will be multiple exceptions. If that is not currently a supported way to use <ErrorBoundary> we can close this issue. Of course, that would be nice to see eventually :)

[TanayParikh]

I'll leave this open to confirm if there are any restrictions with respect to ErrorBoundary's and multiple exceptions.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[thirstyape]

@TanayParikh I did some further testing today and I believe that we can close this out. I was able to use the sample project and get everything to work as expected as long as there was a single exception.

I pushed my changes to the test. With these updates, the ErrorBoundary now works as expected and can be re-used as many times as needed. That is, it will not stop working after the first time. Simply clicking the reset button I added will allow the process to repeat.

I think we can reasonably conclude that the multiple exceptions was the cause and is not currently a supported scenario.

[TanayParikh]

Thanks @thirstyape, let's keep this issue open to track potentially adding support for multiple exceptions in the future.

[ghost]

Thank you for contacting us. Due to a lack of activity on this discussion issue we're closing it in an effort to keep our backlog clean. If you believe there is a concern related to the ASP.NET Core framework, which hasn't been addressed yet, please file a new issue.

This issue will be locked after 30 more days of inactivity. If you still wish to discuss this subject after then, please create a new issue!

[TanayParikh]

@SteveSandersonMS would you like to keep this open?

[SteveSandersonMS]

Sure, let's reopen and keep on backlog.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[eduard-tapkey]

Are there any updates on this topic? One year later it seems multiple exceptions at once are not supported by ErrorBoundary. The ErrorContent won't render.

[zerox981]

This bug is making the ErrorBoundary useless for real world scenarios. As soon as we have more than 1 component failing (in OnInitialized(Async), OnParameterSet(Async), nothing gets rendered on the screen (the render code is executed, but there is no output).