dotnet/wpf · error · ArgumentException

SR.Format(SR.DragDrop_DragActionInvalid, "value")

Error message

SR.Format(SR.DragDrop_DragActionInvalid, "value")

What it means

QueryContinueDragEventArgs.Action accepts only values validated by DragDrop.IsValidDragAction: DragAction.Continue, Drop, or Cancel. Setting any other value (e.g. a cast integer or uninitialized enum) throws an ArgumentException with the parameter name 'value'.

Solutions

Only assign DragAction.Continue, DragAction.Drop, or DragAction.Cancel.
Validate numeric input with Enum.IsDefined(typeof(DragAction), v) before casting.
Map native DROPEFFECT constants to the proper DragAction explicitly instead of blind casts.
Wrap the assignment in validation logic in the drag handler.

Example fix

// before
e.Action = (DragAction)nativeEffect; // may be out of range

// after
e.Action = (nativeEffect & DROPEFFECT_MOVE) != 0 ? DragAction.Drop : DragAction.Continue;

Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined(typeof(DragAction), value))
    throw new ArgumentException($"Invalid DragAction: {value}");

Type guard

static bool IsValidDragAction(DragAction a) =>
    a == DragAction.Continue || a == DragAction.Drop || a == DragAction.Cancel;

Try / catch

try { args.Action = desiredAction; }
catch (ArgumentException ex) when (ex.Message.Contains("value"))
{ args.Action = DragAction.Cancel; }

Prevention

Never cast raw ints or native DROPEFFECT values directly to DragAction.
Validate configuration-driven drag behavior with Enum.IsDefined.
Use only the three documented DragAction members.

When it happens

Trigger: In a QueryContinueDrag handler, assigning e.Action = (DragAction)someInt or an out-of-range value; data-binding or reflection-driven property assignment with invalid enum data.

Common situations: Custom drag controllers storing drag state as int and casting; settings-driven drag behavior where configuration values are not validated; interop code mapping native DROPEFFECT values directly onto DragAction.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/28e563d365835e4c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/QueryContinueDragEventArgs.cs:81

        {
            get {return _dragDropKeyStates;}
        }

        /// <summary>
        /// The action of drag operation
        /// </summary>
        public DragAction Action
        {
            get 
            {   
                return _action;
            }

            set 
            {
                if (!DragDrop.IsValidDragAction(value))
                {
                    throw new ArgumentException(SR.Format(SR.DragDrop_DragActionInvalid, "value"));
                }

                _action = value; 
            }
        }

        #endregion Public Methods

        #region Protected Methods

        //------------------------------------------------------
        //
        //  Protected Methods
        //
        //------------------------------------------------------

        /// <summary>
        /// The mechanism used to call the type-specific handler on the target.

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