unoplatform/uno · error · Error

retrieveFiles failed to find pending drag and drop data for

Error message

retrieveFiles failed to find pending drag and drop data for id ${pendingDropId}.

What it means

Thrown by BrowserDragDropExtension.retrieveText when the static _idToContent Map does not contain an entry for the given pendingDropId. The _idToContent map is populated ONLY inside the 'drop' DOM event handler (line 56 of onDragDropEvent) and removed explicitly via removeId. Note: the message text incorrectly says 'retrieveFiles' even though this is the retrieveText method (copy-paste bug in the error string). This indicates the C# caller passed a drop ID that was never registered or was already consumed.

Source

Thrown at src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserDragDropExtension.ts:99

			}
		}

		private static beginRetrieveItems(data: DataTransfer): Array<Promise<FileSystemHandle | File | string | null>> {
			const promises: Array<Promise<FileSystemHandle | File | string | null>> = [];
			for (let i = 0; i < data.items.length; i++) {
				if (data.items[i].kind == "string") {
					promises.push(BrowserDragDropExtension.getText(data.items[i]));
				} else {
					promises.push(BrowserDragDropExtension.getAsFile(data.items[i]));
				}
			}
			return promises;
		}

		public static retrieveText(pendingDropId: number, itemId: number): Promise<string> {
			const data = BrowserDragDropExtension._idToContent.get(pendingDropId);
			if (!data) {
				throw new Error(`retrieveFiles failed to find pending drag and drop data for id ${pendingDropId}.`);
			}

			return data[itemId] as Promise<string>;
		}

		public static async retrieveFiles(pendingDropId: number, itemIds: Int32Array): Promise<string> {
			const data = BrowserDragDropExtension._idToContent.get(pendingDropId);
			if (!data) {
				throw new Error(`retrieveFiles failed to find pending drag and drop data for id ${pendingDropId}.`);
			}

			const selected = Array.from(itemIds).map(i => data[i] as Promise<FileSystemHandle | File>);
			const fileHandles = await Promise.all(selected);
			const infos = Uno.Storage.NativeStorageItem.getInfos(...fileHandles);
			return JSON.stringify(infos);
		}

		public static removeId(id: number) {

View on GitHub (pinned to 0418340488)

Solutions

Ensure retrieveText is called exactly once per drop event, using the pendingDropId delivered by the OnNativeDropEvent dispatch (the same id set in onDragDropEvent on dragenter).
Do not call removeId until all item content has been fully retrieved for that drop id.
If you need to retrieve multiple items, batch them in a single retrieveFiles/retrieveText call chain before removeId.

Example fix

// before: retrieve then immediately remove
BrowserDragDropExtension.retrieveText(dropId, 0);
BrowserDragDropExtension.removeId(dropId);
BrowserDragDropExtension.retrieveText(dropId, 1); // throws — id already removed

// after: retrieve all items first, then remove
const t0 = BrowserDragDropExtension.retrieveText(dropId, 0);
const t1 = BrowserDragDropExtension.retrieveText(dropId, 1);
await Promise.all([t0, t1]);
BrowserDragDropExtension.removeId(dropId);

Defensive patterns

Strategy: validation

Validate before calling

// Before calling retrieveText, verify the drop id still has content
const data = BrowserDragDropExtension['_idToContent']?.get(pendingDropId);
if (!data) {
    // drop id not staged — do not call retrieveText
    return null;
}

Try / catch

try {
    const text = await BrowserDragDropExtension.retrieveText(dropId, itemId);
} catch (e) {
    if (e.message.includes('failed to find pending drag and drop data')) {
        // drop content already consumed/cleared — handle gracefully
    } else { throw e; }
}

Prevention

Track which drop ids have been consumed and avoid double-retrieval.
Call removeId only after all retrieveText/retrieveFiles calls for that id have resolved.
Log the pendingDropId at dragenter and at retrieve time to catch mismatches early.

When it happens

Trigger: C# calls retrieveText(pendingDropId, itemId) after the drop content was already retrieved and removeId was called, or before a 'drop' event has fired (the map is only filled on drop, not dragenter), or with a stale/wrong pendingDropId.

Common situations: Double-retrieval of the same drop payload (C# calls retrieveText twice for the same drop), calling retrieve after the browser already cleared the DataTransfer, or a mismatch between the pendingDropId captured in dragenter and the one passed to retrieveText.

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/ec6ef9979aba9794. Report an issue: GitHub.