dotnet/aspnetcore · error · Error

There is no file with ID

Error message

There is no file with ID ${fileId}. The file list may have changed. See https://aka.ms/aspnet/blazor-input-file-multiple-selections.

What it means

`getFileById` looks up a browser file the user selected via Blazor's `InputFile` component by indexing `elem._blazorFilesById[fileId]`. Each selected file is assigned an incremental ID by the framework; the map only lives for the lifetime of the current input's file list. If the requested ID is absent the lookup throws, pointing at the multiple-selections guidance because re-picking or clearing files renumbers the list.

Solutions

1. Re-read files in the same `OnInputFileChange` handler where the `IBrowserFile` was obtained — do not retain the id past the current selection.
2. If you must process asynchronously, copy the stream to memory/storage first, then release the id before the user can change the selection.
3. Clear the input (`InputFile.Reset()`) deliberately rather than letting the user re-pick, so the id lifecycle is explicit.
4. On Blazor Server, guard long-running file work against circuit reconnects which can invalidate the client-side file map.

Example fix

// before
var file = e.GetMultipleFiles(int.MaxValue)[0];
// ...user picks new files, then later:
await using var fs = file.OpenReadStream(); // stale id -> throw

// after
var file = e.GetMultipleFiles(int.MaxValue)[0];
await using var ms = new MemoryStream();
await using (var fs = file.OpenReadStream(maxAllowedSize: long.MaxValue))
    await fs.CopyToAsync(ms); // consume immediately, same selection

function hasFile(elem: HTMLInputElement, fileId: number): boolean {
  return !!(elem as any)._blazorFilesById && fileId in (elem as any)._blazorFilesById;
}

try { return await readFileData(elem, fileId); }
catch (e) { if (/no file with ID/.test(e.message)) { /* re-prompt user or abort */ return null; } throw e; }

When it happens

Trigger: Calling `readFileData`/`getFileById` (through `IBrowserFile` open-read APIs or `InputFile` JS interop) with a `fileId` that was never assigned, was assigned on a different input element, or became invalid after the file list changed (re-select, clear, or multiple-selection changes).

Common situations: Caching an `IBrowserFile` reference across postbacks in Blazor Server after the input's file list was replaced; passing an id from a disposed/cleared `<InputFile>`; using the same input for multiple selection rounds and referencing a stale id from an earlier round; desync between server-tracked ids and client `_blazorFilesById` after a reconnect.

Related errors

• Interop methods are already registered for renderer
• Interop methods are not registered for renderer
• No interop methods are registered for renderer
• Cannot update existing state: previous state has not been…
• Could not find ' ' (' ' was undefined).

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/01df505ee37907f5. Report an issue: GitHub.

Appendix: source

Thrown at src/Components/Web.JS/src/InputFile.ts:117

    contentType: format,
    blob: resizedImageBlob ? resizedImageBlob : originalFile.blob,
  };

  elem._blazorFilesById[result.id] = result;

  return result;
}

async function readFileData(elem: InputElement, fileId: number): Promise<Blob> {
  const file = getFileById(elem, fileId);
  return file.blob;
}

export function getFileById(elem: InputElement, fileId: number): BrowserFile {
  const file = elem._blazorFilesById[fileId];

  if (!file) {
    throw new Error(`There is no file with ID ${fileId}. The file list may have changed. See https://aka.ms/aspnet/blazor-input-file-multiple-selections.`);
  }

  return file;
}

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