Question

在ClojureScript中，可以将要解构的原始项目存储在单独的值中。例如，当使用地图{:a "A" :b "B" :c 3 :d 4}调用下面的匿名函数时，密钥a和b将被解构，原始地图将使用m存储在:as中操作

((fn [{:keys [a b] :as m}]
   (println "a is" a)
   (println "b is" b)
   (println "m is" m))
  {:a "A" :b "B" :c 3 :d 4})

;; => a is A
;;    b is B
;;    m is {:a "A" :b "B" :c 3 :d 4}
;;    nil

ECMAScript中是否有类似的操作？如，

(({ a, b }) => {
  console.log(`a = ${a}`);
  console.log(`b = ${b}`);
  console.log(`m = ${???}`);
})({ a: "A", b: "B", c: 3, d: 4 });

或者是否有必要先将原始项目存储在变量中并稍后进行解构？

((m) => {
  const { a, b } = m;
  console.log(`a is ${a}`);
  console.log(`b is ${b}`);
  console.log(`m is ${m}`);
})({ a: "A", b: "B", c: 3, d: 4 });

;; => a is A
;;    b is B
;;    m is [Object object]

Answer 1

如果要访问原始参数，则应将其解构为函数体中的变量：

public class MainActivity extends AppCompatActivity {

    FloatingActionButton fab;
    Animation show_fab;
    Animation hide_fab;
    private List<Movie> movieList = new ArrayList<>();
    MyAdapter mAdapter;
    RecyclerView recycler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fab = (FloatingActionButton) findViewById(R.id.fab);
        show_fab = AnimationUtils.loadAnimation(getApplication(), R.anim.fab_show);
        hide_fab = AnimationUtils.loadAnimation(getApplication(), R.anim.fab_hide);

        recycler = (RecyclerView)findViewById(R.id.recycler);
        recycler.setLayoutManager(new LinearLayoutManager(MainActivity.this, LinearLayoutManager.VERTICAL, false));
        recycler.setHasFixedSize(true);

        mAdapter = new MyAdapter(movieList);
        recycler.setAdapter(mAdapter);

        prepareMovieData();

        recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                if (dy > 0 && (fab.getVisibility() == View.VISIBLE)){
                    //fab.hide();
                    fab.startAnimation(hide_fab);
                }
                else if (dy < 0 && (fab.getVisibility() != View.VISIBLE)){
                    //fab.show();
                    fab.startAnimation(show_fab);
                }
            }
        });
    }

    private void prepareMovieData() {
        Movie movie = new Movie("Mad Max: Fury Road", "Action & Adventure", "2015");
        movieList.add(movie);

        movie = new Movie("Inside Out", "Animation, Kids & Family", "2015");
        movieList.add(movie);

        movie = new Movie("Star Wars: Episode VII - The Force Awakens", "Action", "2015");
        movieList.add(movie);

        movie = new Movie("Shaun the Sheep", "Animation", "2015");
        movieList.add(movie);

        movie = new Movie("The Martian", "Science Fiction & Fantasy", "2015");
        movieList.add(movie);

        movie = new Movie("Mission: Impossible Rogue Nation", "Action", "2015");
        movieList.add(movie);

        movie = new Movie("Up", "Animation", "2009");
        movieList.add(movie);

        movie = new Movie("Star Trek", "Science Fiction", "2009");
        movieList.add(movie);

        movie = new Movie("The LEGO Movie", "Animation", "2014");
        movieList.add(movie);

        movie = new Movie("Iron Man", "Action & Adventure", "2008");
        movieList.add(movie);

        movie = new Movie("Aliens", "Science Fiction", "1986");
        movieList.add(movie);

        movie = new Movie("Chicken Run", "Animation", "2000");
        movieList.add(movie);

        movie = new Movie("Back to the Future", "Science Fiction", "1985");
        movieList.add(movie);

        movie = new Movie("Raiders of the Lost Ark", "Action & Adventure", "1981");
        movieList.add(movie);

        movie = new Movie("Goldfinger", "Action & Adventure", "1965");
        movieList.add(movie);

        movie = new Movie("Guardians of the Galaxy", "Science Fiction & Fantasy", "2014");
        movieList.add(movie);

        mAdapter.notifyDataSetChanged();
    }

    public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

        private List<Movie> moviesList;

        public MyAdapter(List<Movie> moviesList) {
            this.moviesList = moviesList;
        }

        @Override
        public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View itemView = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.movie_list_row, parent, false);

            return new MyViewHolder(itemView);
        }

        @Override
        public void onBindViewHolder(MyViewHolder holder, int position) {
            Movie movie = moviesList.get(position);
            holder.title.setText(movie.getTitle());
            holder.genre.setText(movie.getGenre());
            holder.year.setText(movie.getYear());
        }

        @Override
        public int getItemCount() {
            return moviesList.size();
        }

        public class MyViewHolder extends RecyclerView.ViewHolder {
            public TextView title, year, genre;

            public MyViewHolder(View view) {
                super(view);
                title = (TextView) view.findViewById(R.id.title);
                genre = (TextView) view.findViewById(R.id.genre);
                year = (TextView) view.findViewById(R.id.year);
            }
        }
    }


}

即使没有访问它，这种风格也是有益的，因为它允许在出现问题时调试参数，尤其是在(m) => { const { a, b } = m; ... }不可用的原生箭头函数中。

访问已解构的项目

1 个答案: