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Вячеслав
Asked:2020-09-20 01:50:28 +0000 UTC2020-09-20 01:50:28 +0000 UTC

如何将 url 传递给 Book 类的新实例？

  • 772

如何在这段代码中将方法initData()传递url给对象Book？从服务器上Url解析。json

public class MainActivity extends AppCompatActivity {
    public static String LOG_TAG = "my_log";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setHasFixedSize(true);
        RecyclerAdapter adapter = new RecyclerAdapter(initData());
        recyclerView.setAdapter(adapter);

//        new ParseTask().execute();
    }


    private class ParseTask extends AsyncTask<Void, Void, String> {

        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;
        String resultJson = "";

        @Override
        protected String doInBackground(Void... params) {
            // получаем данные с внешнего ресурса
            try {
                URL url = new URL("http://*********/todbook/booklist.json");

                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();

                reader = new BufferedReader(new InputStreamReader(inputStream));

                String line;
                while ((line = reader.readLine()) != null) {
                    buffer.append(line);
                }

                resultJson = buffer.toString();

            } catch (Exception e) {
                e.printStackTrace();
            }
            return resultJson;
        }

        @Override
        protected void onPostExecute(String strJson) {
            super.onPostExecute(strJson);
            // выводим целиком полученную json-строку
            Log.d(LOG_TAG, strJson);

            JSONObject dataJsonObj = null;

            try {
                dataJsonObj = new JSONObject(strJson);
                JSONArray books = dataJsonObj.getJSONArray("books");

                // 2. перебираем и выводим url обложек
                for (int i = 0; i < books.length(); i++) {
                    JSONObject book = books.getJSONObject(i);
                    String url_book = book.getString("coverUrl");
                    Log.d(LOG_TAG, "coverUrl: " + url_book);
                }

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * массив для показа обложек книг
     */
    private List<Book> initData() {
        ArrayList<Book> books1 = new ArrayList<>();
        new ParseTask().execute();
        books1.add(new Book("wwww"));
        books1.add(new Book("wwww"));
        books1.add(new Book("wwww"));
        return books1;
    }
}
java

1 个回答

  1. Best Answer

    您需要编写一个接口Callback，它将成为AsyncTask'th的观察者

     interface Callback {
     void onPreExecute();
     void onPostExecute(ArrayList<String> urls); 
 }

    AsyncTask拉方法Calback'a

    class ParseTask extends AsyncTask<Void, Void, String> {
    Callback callback;

    public ParseTask(Callback callback) {//передать в конструктор
        this.callback = callback;
    }

    @Override
    protected void onPreExecute() {//загрузка началась
        callback.onPreExecute();
    }

    @Override
    protected String doInBackground(Void... voids) {
        return null;
    }

    @Override
    protected void onPostExecute(String string) {//загрузка закончилась
        //parse
        callback.onPostExecute(new ArrayList<String>());//передать данные
    }
}

    传递Callback给构造函数并调用execute()

    new ParseTask(new Callback(){
    @Override
    public void onPreExecute() {
        //show progress
    }

    @Override
    public void onPostExecute(ArrayList<String> urls) {
        //hide progress
        RecyclerAdapter adapter = new RecyclerAdapter(initData(urls)); //передать полученные урлы
        recyclerView.setAdapter(adapter);
    }
}).execute();
    • 0

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