Add value to TreeDataTransferItem dnd API

src/vs/workbench/api/common/extHostTypes.ts

@@ -2315,10 +2315,10 @@ export enum TreeItemCollapsibleState {
 @es5ClassCompat
 export class TreeDataTransferItem {
 	async asString(): Promise<string> {
-		return JSON.stringify(this._value);
+		return JSON.stringify(this.value);
 	}
 
-	constructor(private readonly _value: any) { }
+	constructor(public readonly value: any) { }
 }
 
 @es5ClassCompat

src/vs/workbench/api/common/shared/treeDataTransfer.ts

@@ -19,7 +19,8 @@ export namespace TreeDataTransferConverter {
 		const newDataTransfer: ITreeDataTransfer = new Map<string, ITreeDataTransferItem>();
 		value.types.forEach((type, index) => {
 			newDataTransfer.set(type, {
-				asString: async () => value.items[index].asString
+				asString: async () => value.items[index].asString,
+				value: undefined
 			});
 		});
 		return newDataTransfer;

src/vs/workbench/browser/parts/views/treeView.ts

@@ -1382,7 +1382,8 @@ export class CustomTreeViewDragAndDrop implements ITreeDragAndDrop<ITreeItem> {
 								willDropUuid = dataValue;
 							} else {
 								treeDataTransfer.set(type, {
-									asString: () => Promise.resolve(dataValue)
+									asString: () => Promise.resolve(dataValue),
+									value: undefined
 								});
 							}
 							decrementStringCount();

src/vs/workbench/common/views.ts

@@ -637,6 +637,7 @@ export interface IViewDescriptorService {
 
 export interface ITreeDataTransferItem {
 	asString(): Thenable<string>;
+	value: any;
 }
 
 export type ITreeDataTransfer = Map<string, ITreeDataTransferItem>;

src/vscode-dts/vscode.proposed.treeViewDragAndDrop.d.ts

@@ -29,24 +29,13 @@ declare module 'vscode' {
 	/**
 	 * A class for encapsulating data transferred during a tree drag and drop event.
 	 *
-	 * If your `DragAndDropController` implements `handleDrag`, you can extend `TreeDataTransferItem` and return
-	 * an instance of your new class for easy access to the source tree items.
-	 *
-	 * ```ts
-	 * 	class TestViewObjectTransferItem extends vscode.TreeDataTransferItem {
-	 * 		constructor(private _nodes: Node[]) {
-	 * 			super(_nodes);
-	 * 		}
-	 *
-	 * 		asObject(): Node[] {
-	 * 			return this._nodes;
-	 * 		}
-	 * 	}
-	 * ```
+	 * If your `DragAndDropController` implements `handleDrag`, you can use the `value` of the `TreeDataTransferItem`
+	 * to get back the object you put into it so long as the extension that created the `TreeDataTransferItem` runs in the same
+	 * extension host.
 	 */
 	export class TreeDataTransferItem {
 		asString(): Thenable<string>;
-
+		readonly value: any;
 		constructor(value: any);
 	}