---
title: "draggingSession(_:sourceOperationMaskFor:)"
framework: appkit
role: symbol
role_heading: Instance Method
path: "appkit/nsdraggingsource/draggingsession(_:sourceoperationmaskfor:)"
---

# draggingSession(_:sourceOperationMaskFor:)

Declares the types of operations the source allows to be performed.

## Declaration

```swift
@MainActor func draggingSession(_ session: NSDraggingSession, sourceOperationMaskFor context: NSDraggingContext) -> NSDragOperation
```

## Parameters

- `session`: The dragging session.
- `context`: The dragging context. See doc://com.apple.appkit/documentation/AppKit/NSDraggingContext for the supported values.

## Return Value

Return Value A dragging operation you specify.

## Discussion

Discussion To account for unexpected contexts, set a default case for the most specific context your app handles. The following code shows an example that handles different dragging contexts and includes a default case.     switch(context) {         case NSDraggingContextOutsideApplication:             return NSDragOperationCopy;           case NSDraggingContextWithinApplication:         default:             return NSDragOperationCopy | NSDragOperationMove;     }