class_docstr: XCollector is a data collector which takes processed related prediction probabilities to calculate Fidelity+
  and Fidelity-.
  
  Args:
      sparsity (float): The Sparsity is use to transform the soft mask to a hard one.
  
  .. note::
      For more examples, see `benchmarks/xgraph
      <https://github.com/divelab/DIG/tree/dig/benchmarks/xgraph>`_.
code: def targets(self) -> list:
      return self.__targets
  
imports: import torch
  import torch.nn
  from typing import List, Union
  from torch import Tensor
  import numpy
  from torch_geometric.data.data import Data
  from torch_geometric.nn import MessagePassing
label_desc: Use image node_id 2 for calling the XCollector obj's underlying member method code with example usage: obj.targets() and returns: self