uwp - Drag accepted operation not observed

Question

Rather strange but I'm at my wit's end. I have this DragOver handler, practically out of the book:

  e.DragUIOverride.Caption = "my text";
  var op = DataPackageOperation.None;

  if (e.DataView.Contains(StandardDataFormats.StorageItems)) {
    var items = await e.DataView.GetStorageItemsAsync();
    if (items.Any()) {
      var file = items.First() as StorageFile;
      op = (file?.FileType == ".myext") ? DataPackageOperation.Copy : DataPackageOperation.None;
    }
  }

  System.Diagnostics.Trace.WriteLine(op);
  e.AcceptedOperation = op;

The reason for op is to avoid setting the AcceptedOperation twice (not normally required in samples but one of my desperate attempts). The trace at the end shows that this code sets the exact operation I need, no chance of failure. Yet, when running, all I get is a No Entry sign denoting a denied drag operation.

W10 20H2, for what it's worth.

Answer 1

等待大神答复