PrismLibrary/Prism · error · InvalidOperationException

The constructed URI has a relative back operator after a…

Error message

The constructed URI has a relative back operator after a new Navigation Segment which is not supported - '{uri}'.

What it means

BuildUri also rejects a URI where a '..' back operator appears AFTER a real navigation segment, since .NET MAUI/Prism navigation cannot pop and then descend within a single URI in that order. It throws InvalidOperationException identifying the constructed URI.

Solutions

Reorder segments: put all RelativeBack() calls first, then the page segments to descend into: RelativeBack().AddSegment("DetailPage").
Split navigation into two calls if you need pop-then-push semantics (GoBackAsync then NavigateAsync).
Validate the segment list before building: reject any '..' appearing after a non-'..' segment.

Example fix

// before
navigationService.CreateBuilder().AddSegment("DetailPage").RelativeBack().NavigateAsync(); // back after segment
// after
navigationService.CreateBuilder().RelativeBack().AddSegment("DetailPage").NavigateAsync(); // back first

Defensive patterns

Strategy: validation

Validate before calling

bool backAfterSegment = false; bool hasPage = false;
foreach (var s in segments)
{
    if (s == "..") { if (hasPage) { backAfterSegment = true; break; } }
    else hasPage = true;
}
if (backAfterSegment) throw new InvalidOperationException("All '..' segments must precede page segments.");

Try / catch

try
{
    await navigationService.NavigateAsync(uri);
}
catch (InvalidOperationException ex) when (ex.Message.Contains("after a new Navigation Segment"))
{
    logger.LogError(ex, "Navigation segments out of order: {Uri}", uri);
}

Prevention

Always build URIs as [.. ']* followed by page segments.
Use RelativeBack() extension at the start of the chain, then AddSegment calls.
Split pop-then-push needs into GoBackAsync() + NavigateAsync() calls.

When it happens

Trigger: Building segments in the order [page segment, '..', ...] — e.g. AddSegment("DetailPage").RelativeBack() — then calling NavigateAsync(); the loop detects hasNonBackSegment followed by a '..' segment.

Common situations: Misunderstanding that RelativeBack must precede new segments (it walks up first); assembling segments from user input or config in the wrong order; refactoring that appends a back step after navigating deeper.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/4468d8711ae4298b. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Builder/NavigationBuilder.cs:118

    internal Uri BuildUri()
    {
        var uri = (_absoluteNavigation ? "/" : string.Empty) +
            string.Join("/", _uriSegments.Select(x => x.Segment));

        if(uri.Contains("../"))
        {
            if (_absoluteNavigation)
                throw new InvalidOperationException("The generated URI has one or more relative back operators and was marked as an absolute path. This is not supported.");

            var segments = uri.Split('/');
            if (!segments.Any(x => x != ".."))
                throw new InvalidOperationException($"The constructed URI contains one or more relative back operators, but contains no other navigation segments - '{uri}'.");
            var hasNonBackSegment = false;
            for(int i = 0; i < segments.Length; i++)
            {
                if (hasNonBackSegment && segments[i] == "..")
                    throw new InvalidOperationException($"The constructed URI has a relative back operator after a new Navigation Segment which is not supported - '{uri}'.");
                else if (segments[i] != "..")
                    hasNonBackSegment = true;
            }
        }

        return UriParsingHelper.Parse(uri);
    }
}

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