dotnet/wpf · error · ArgumentException

SR.BadTextPositionOrder

Error message

SR.BadTextPositionOrder

What it means

ValidationHelper.VerifyPositionPair throws ArgumentException(SR.BadTextPositionOrder) when a start TextPointer compares greater than an end TextPointer. The library requires all start/end position pairs to be ordered so that start <= end; passing a reversed pair would break TextRange/TextSegment invariants. This is a pre-condition check on the public text-position API surface.

Solutions

  1. Swap the arguments so the earlier TextPointer is passed as startPosition.
  2. Call startPosition.CompareTo(endPosition) before invoking and swap if > 0.
  3. Verify both pointers come from the same TextContainer and represent the intended logical order.

Example fix

// before
new TextRange(endPointer, startPointer);
// after
if (startPointer.CompareTo(endPointer) > 0) { var t = startPointer; startPointer = endPointer; endPointer = t; }
new TextRange(startPointer, endPointer);
Defensive patterns

Strategy: validation

Validate before calling

if (start == null || end == null) throw new ArgumentNullException(nameof(start));
if (start.CompareTo(end) > 0) (start, end) = (end, start);

Try / catch

try { ... } catch (ArgumentException ex) { /* handle reversed/rejected positions */ }

Prevention

When it happens

Trigger: Calling any API that takes (startPosition, endPosition) where startPosition.TextContainer == endPosition.TextContainer but startPosition.CompareTo(endPosition) > 0 — e.g. constructing a TextRange or selecting a range with the later position passed as 'start'.

Common situations: Constructing ranges from user-selection data where start/end were swapped; computing positions asynchronously and passing them back in reverse order; copying positions from two different selections.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/326ad88dda4f4259. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/ValidationHelper.cs:63

            }
        }

        // Verifies two positions are safe to use as a logical text span.
        //
        // Throws ArgumentNullException if startPosition == null || endPosition == null
        //        ArgumentException if startPosition.TextContainer != endPosition.TextContainer or
        //                             startPosition > endPosition
        internal static void VerifyPositionPair(ITextPointer startPosition, ITextPointer endPosition)
        {
            ArgumentNullException.ThrowIfNull(startPosition);
            ArgumentNullException.ThrowIfNull(endPosition);
            if (startPosition.TextContainer != endPosition.TextContainer)
            {
                throw new ArgumentException(SR.Format(SR.InDifferentTextContainers, "startPosition", "endPosition"));
            }
            if (startPosition.CompareTo(endPosition) > 0)
            {
                throw new ArgumentException(SR.Format(SR.BadTextPositionOrder, "startPosition", "endPosition"));
            }
        }

        // Throws an ArgumentException if direction is not a valid enum.
        internal static void VerifyDirection(LogicalDirection direction, string argumentName)
        {
            if (direction != LogicalDirection.Forward &&
                direction != LogicalDirection.Backward)
            {
                throw new InvalidEnumArgumentException(argumentName, (int)direction, typeof(LogicalDirection));
            }
        }

        // Throws an ArgumentException if edge is not a valid enum.
        internal static void VerifyElementEdge(ElementEdge edge, string param)
        {
            if (edge != ElementEdge.BeforeStart &&
                edge != ElementEdge.AfterStart  &&

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