mapDispatchToProps参数可以是undefined、对象或函数。如果它是undefined，react-redux将把dispatch添加到props中。
下面是3个例子，你可以如何使用它与undefined，一个函数或一个对象和一个例子与react-redux hooks。我建议使用钩子，因为这是React的发展方向（而不是像连接一样的HOC）。

const {
  Provider,
  connect,
  useSelector,
  useDispatch,
} = ReactRedux;
const { createStore, applyMiddleware, compose } = Redux;

const initialState = {
  items: [{ id: 1, name: 'item 1' }],
};
//action types
const DELETE = 'DELETE';
//action creators
const deleteItem = (id) => ({
  type: DELETE,
  payload: id,
});
const reducer = (state, { type, payload }) => {
  console.log('action:', type, 'payload:', payload);
  return state;
};
//creating store with redux dev tools
const composeEnhancers =
  window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
const store = createStore(
  reducer,
  initialState,
  composeEnhancers(
    applyMiddleware(() => (next) => (action) =>
      next(action)
    )
  )
);
//you should use reselect here but for simplicity I didn't
const mapStateToProps = (state, { id }) => ({
  item: state.items.find((item) => item.id === id),
});
//if mapDispatchToProps is undefined then react-redux
//  will add dispatch to props, here is how you can delete
const ItemMapDispatchUndefined = ({ item, dispatch }) => (
  <button onClick={() => dispatch(deleteItem(item.id))}>
    undefined - delete {item.name}
  </button>
);
const ConnectedDispatchUndefined = connect(mapStateToProps)(
  ItemMapDispatchUndefined
);
//if mapDispatchToProps is an object then react-redux
//  will take the properties of that object and if a
//  property is a functoin it will wrap that function
//  in a new function that will automatically dispatch
//  the return value when that function is called
const ItemMapDispatchObject = ({ item, deleteItem }) => (
  // no dispatch needed but still need to pass id to deleteItem
  <button onClick={() => deleteItem(item.id)}>
    object - delete {item.name}
  </button>
);
const ConnectedDispatchObject = connect(mapStateToProps, {
  deleteItem,
})(ItemMapDispatchObject);
//if mapDispatchToProps is a function then that function needs
//  to return an object where each property of that object is a
//  function that will dispatch an action. These properties
//  will be added to component props by react-redux
const ItemMapDispatchFunction = ({ item, deleteItem }) => (
  // no dispatch needed and no id needs to be passed
  <button onClick={deleteItem}>
    function - delete {item.name}
  </button>
);
const ConnectedItem3 = connect(
  mapStateToProps,
  (dispatch, { id }) => ({
    deleteItem: () => dispatch(deleteItem(id)),
  })
)(ItemMapDispatchFunction);
//using hooks (not using connect at all)
const Hooks = ({ id }) => {
  //should use reselect but for simplicity not used
  const item = useSelector((state) =>
    state.items.find((item) => item.id === id)
  );
  const dispatch = useDispatch();
  return (
    <button onClick={() => dispatch(deleteItem(item.id))}>
      hooks - delete {item.name}
    </button>
  );
};

const App = () => {
  return (
    <div>
      <ConnectedDispatchUndefined id={1} />
      <ConnectedDispatchObject id={1} />
      <ConnectedItem3 id={1} />
      <Hooks id={1} />
    </div>
  );
};

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById('root')
);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.4/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.4/umd/react-dom.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/redux/4.0.5/redux.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-redux/7.2.0/react-redux.min.js"></script>
<div id="root"></div>