When to reuse cut and when to find it again?

[danielchalmers]

A change to the MudBlazor MudDialog was made in https://github.com/MudBlazor/MudBlazor/pull/8964/files which changed asynchrony and caused my tests to fail with Bunit.Rendering.ComponentNotFoundException : A component of type EditNoteDialog was not found in the render tree..

[Fact]
public void Note()
{
[...]
    var cut = layout.FindComponent<DataPointView>();

    cut.Find(".mud-link").Click();

    var noteEditor = layout.FindComponent<EditNoteDialog>();
    noteEditor.Find("textarea").Input("123");
    layout.Find(".submit-button").Click();

    point.Text.Should().Be("123");

    cut.Find(".mud-link").Click();

    noteEditor = layout.FindComponent<EditNoteDialog>();
    noteEditor.Find("textarea").Input("EXTRA TEXT THAT WILL BE DISCARDED");
    layout.Find(".cancel-button").Click();

    point.Text.Should().Be("123");
}

but making these changes fixes it:

[Fact]
public void Note()
{
[...]
    var cut = () => layout.FindComponent<DataPointView>();

    cut().Find(".mud-link").Click();

    var noteEditor = () => layout.FindComponent<EditNoteDialog>();
    noteEditor().Find("textarea").Input("123");
    layout.Find(".submit-button").Click();

    point.Text.Should().Be("123");

    cut().Find(".mud-link").Click();

    noteEditor().Find("textarea").Input("EXTRA TEXT THAT WILL BE DISCARDED");
    layout.Find(".cancel-button").Click();

    point.Text.Should().Be("123");
}

Is this the preferred way of doing it: var cut = () => layout.FindComponent<DataPointView>();? We've made several similar changes in the MudBlazor codebase but want to double check that it's supported!

[danielchalmers]

Something interesting:

[...] when a Task method becomes truly asynchronous: async Task SomeTask => await Task.CompletedTask vs async Task SomeTask => await Task.Delay(x), the Find methods start to behave differently.

MudBlazor/MudBlazor#9030 (comment)

[ScarletKuro]

Looks like my comment isn't accurate, since apparently it's still failing (MudBlazor/MudBlazor#9030 (comment)), but I still think it has nothing to do with the MudBlazor code. Why does the test fail when you run tests in batch and not when you run them individually? Something could be wrong with the configuration. If anyone has an idea, please share.
Btw, this isn't reproducible with NUnit when @danielchalmers tried.

[ScarletKuro]

What I see is that the layout.FindComponent<EditNoteDialog>() will kick in before await dialogReference.Result in that case. I'll just revert this PR; I don't really have that much time to spend more on it. I added this because it was done in Blazored/Modal (Blazored/Modal#408) and our dialogs are basically the same.

[ScarletKuro]

Btw, somehow similar #1064 and #1456, tho unlike the last one we don't use any Task.Run, just the RunContinuationsAsynchronously for TaskCompletionSource, but both will result running the code on the ThreadPool(?)

[danielchalmers]

Putting this on hold so I can get more info

[egil]

Hey there,

When you call cut.FindComponent<TComponent>(), it will search down the component tree from the current component (cut), until it finds the first component that matches TComponent. If a render causes this component to be removed from the component tree, the instance returned from the previous call to FindComponent will be in a disposed/disconnected state, and no longer representing the current state of the component tree.

So whether or not you need to re-issue a FindComponent call depends on whether or not the found component gets removed and then recreated in the component tree between interactions. That is obviously very scenario specific, so there is no general rule I can give you.