SteveSandersonMS
commented
10 months ago I'm afraid you can't do this:
<FluentTreeView>
@{
RenderTree(0, 3);
void RenderTree(int depth, int maxDepth)
{
if (depth >= maxDepth)
{
return;
}
<FluentTreeItem Text="item">
@{ RenderTree(depth + 1, maxDepth); }
</FluentTreeItem>
}
}
</FluentTreeView>This is adding procedural logic in the middle of rendering that shares the same RenderTreeBuilder just as a fluke of C# scoping rules. It will write output to the builder in an unsupported order, without any correctness guarantees provided by normal Razor syntax. It's unfortunate that C# local method syntax creates the possibility of this pattern which will not work.
It could be an error with the library (initially reported here https://github.com/microsoft/fluentui-blazor/issues/1289) but this code works fine:
That does work fine because it's returning a real RenderFragment which can be rendered properly.
verdie-g
ghost
[Edit by @SteveSandersonMS] This issue was originally reported by @verdie-g as follows below the line. On investigation the problem is that C# has added a new syntax that doesn't work in Razor.
The Razor compiler allows arbitrary C# code within
@{ ... }blocks. Unfortunately this means it allows the use of local functions in a way that confuses the parsing logic, causing it to use the wrong__builderinstance. Example:Here, the child content of
FluentTreeItemshould be compiled as aRenderFragmentthat acts on whateverRenderTreeBuilderis passed in. But because of C# scoping rules, theRenderFragmentactually acts on the__buildercaptured from its parent context, so it is simply corrupting the output instead of doing something useful.Possible solutions:
@{ ... }specifically. However that's probably impractical because Razor doesn't parse the contents of@{ ... }.RenderTreeBuilderis invoked. For example if the runtime set an "rendering in progress" flag on it before it starts rendering and synchronously unsets that flag at the end of rendering, then it would have caught this case because child components are rendered afterwards (not recursively), so when the child is rendered it would see it's trying to write to a builder that does not have the "rendering in progress" flag set.NullReferenceExceptioninstead of corrupt output. Obviously that's not super easy to understand but avoids any perf cost.Is there an existing issue for this?
Describe the bug
I'm rendering a blazor wasm component using a recursive C# method and while it's working fine using C# only (
OpenComponent,AddAttribute, etc.), it fails when returning HTML from that recursive method.Expected Behavior
I'm expecting a tree structure to be built and clicking on a line should expand its children but it seems like the children are not rendered and an error is thrown on click.
Steps To Reproduce
I was not able to reproduce the issue without the library fluentui-blazor.
Then replace
Home.razorwithClick on the item generated and check the error in the console.
It could be an error with the library (initially reported here https://github.com/microsoft/fluentui-blazor/issues/1289) but this code works fine:
Exceptions (if any)
.NET Version
8.0.101
Anything else?
No response