stride3d/stride · error · ArgumentException

Invalid path [ ] for action [ ]. Expecting last path to be…

Error message

Invalid path [{0}] for action [{1}]. Expecting last path to be a dictionary item

What it means

MemberPathAction.DictionaryRemove requires the last path segment to be a DictionaryPathItem identifying the key to remove. Apply() throws ArgumentException when the final segment is a member, collection item, or array item.

Solutions

  1. Push a dictionary key segment (PushDictionaryItem) as the final path segment before calling DictionaryRemove.
  2. For lists/arrays, use MemberPathAction.CollectionRemove instead.
  3. Validate lastItem is DictionaryPathItem before invoking Apply in generic helper code.

Example fix

// before
var path = new MemberPath();
path.Push(type.GetProperty("Settings"));
path.Apply(root, MemberPathAction.DictionaryRemove, null);
// after
var path = new MemberPath();
path.Push(type.GetProperty("Settings"));
path.PushDictionaryItem("someKey");
path.Apply(root, MemberPathAction.DictionaryRemove, null);
Defensive patterns

Strategy: validation

Validate before calling

var last = path.Items[^1];
if (action == MemberPathAction.DictionaryRemove && last is not DictionaryPathItem)
    throw new InvalidOperationException("DictionaryRemove requires a dictionary-item path segment.");

Type guard

static bool CanDictionaryRemove(MemberPath p) => p.Items.Count > 0 && p.Items[^1] is DictionaryPathItem;

Try / catch

try { path.Apply(root, MemberPathAction.DictionaryRemove, null); }
catch (ArgumentException ex) when (ex.Message.Contains("Expecting last path to be a dictionary item")) { /* push a dictionary-key segment */ }

Prevention

When it happens

Trigger: Calling Apply(root, MemberPathAction.DictionaryRemove, null) on a path that ends with a MemberPathItem (e.g. just the dictionary property) or a CollectionPathItem/ArrayPathItem.

Common situations: Reusing a list-shaped path and switching the action to DictionaryRemove; forgetting to push the dictionary-key segment (PushDictionaryItem) after pushing the dictionary member.

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 stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/5615c9612851a4a3. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Reflection/MemberPath.cs:253

        switch (actionType)
        {
            case MemberPathAction.CollectionAdd:
                if (lastItem is not CollectionPathItem)
                {
                    throw new ArgumentException("Invalid path [{0}] for action [{1}]. Expecting last path to be a collection item".ToFormat(this, actionType));
                }
                break;
            case MemberPathAction.CollectionRemove:
                if (lastItem is not (CollectionPathItem or ArrayPathItem))
                {
                    throw new ArgumentException("Invalid path [{0}] for action [{1}]. Expecting last path to be a collection/array item".ToFormat(this, actionType));
                }
                break;

            case MemberPathAction.DictionaryRemove:
                if (lastItem is not DictionaryPathItem)
                {
                    throw new ArgumentException("Invalid path [{0}] for action [{1}]. Expecting last path to be a dictionary item".ToFormat(this, actionType));
                }
                break;
        }

        var stack = stackTLS;
        try
        {
            object? nextObject = rootObject;

            if (stack == null)
            {
                stack = [];
                stackTLS = stack;
            }
            else
            {
                stack.Clear();
            }

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