java - 查询其他类/Activity 中的变量是否已填充

Question

我是 Java 和 Android 的初学者。我昨天搜索了一整天的解决方案。我想检查第二个 Activity 中的变量是否已填充。或者询问方法“loadAngebote”是否有返回值。执行获取数据的方法是:

public class loadAngebote extends AsyncTask<String, Void, ArrayList<ArtikelAngebot>>{

    String data ="";

    @Override
    protected ArrayList<ArtikelAngebot> doInBackground(String... params){

        try
        {
            URL url = new URL("http://url/file.php");
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while(line != null){
                line = bufferedReader.readLine();
                data = data + line;
            }
            ArrayList<String> listdata = new ArrayList<>();
            JSONArray jArray = new JSONArray(data);
            for(int i =0 ;i <jArray.length(); i++){
                listdata.add(jArray.getString(i));
            }

            JSONArray json = new JSONArray(data);
            String[][] matrix = new String[json.length()][6];

            for (int i=0; i < json.length(); i++) {
                JSONObject obj = json.getJSONObject(i);
                matrix[i][0] = String.valueOf(obj.getInt("ID"));
                matrix[i][1] = String.valueOf(obj.getInt("art_nr"));
                matrix[i][2] = String.valueOf(obj.getDouble("preis"));
                matrix[i][3] = obj.getString("von");
                matrix[i][4] = obj.getString("bis");
                matrix[i][5] = obj.getString("art_link");
            }

            String[] all_ID = new String[matrix.length];
            String[] all_art_nr = new String[matrix.length];
            String[] all_preis = new String[matrix.length];
            String[] all_von = new String[matrix.length];
            String[] all_bis = new String[matrix.length];
            String[] all_link = new String[matrix.length];


            for (int i = 0; i < matrix.length; i++) {
                all_ID[i] = matrix[i][0];
                all_art_nr[i] = matrix[i][1];
                all_preis[i] = matrix[i][2];
                all_von[i] = matrix[i][3];
                all_bis[i] = matrix[i][4];
                all_link[i] = matrix[i][5];
            }

            ArrayList<ArtikelAngebot> dataList = new ArrayList<>();

            for (int i = 0; i < matrix.length; i++) {
                ArtikelAngebot angebote = new ArtikelAngebot(all_art_nr[i], "Für: " + all_preis[i] + " €","Von: " + all_von[i],"Bis: " + all_bis[i], all_link[i]);
                dataList.add(angebote);
            }

            return dataList;   <--------------------------------------------


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

        return null;
    }

    @Override
    protected void onPostExecute(ArrayList<ArtikelAngebot> QueryResult){

        AngeboteListAdapter adapter = new AngeboteListAdapter(AngeboteActivity.this, R.layout.angebote_list_view_adapter, QueryResult);
        mListView.setAdapter(adapter);

    }

}

我需要检查我的应用程序的其他类中是否填充了 dataList:

static String getLocationResultTitle(Context context, List<Location> locations) {
    if(?????dataList_is_filled?????){
        String numLocationsReported = "Text1";
        return numLocationsReported + " \r\n \r\n :) \r\n \r\n" + DateFormat.getDateTimeInstance().format(new Date());
    }else{
        String numLocationsReported = "Text2";
        return numLocationsReported + " \r\n \r\n :( \r\n \r\n" + DateFormat.getDateTimeInstance().format(new Date());

    }

Answer 1

更新的答案

这是您的AngeboteActivity

public class AngeboteActivity extends AppCompatActivity {

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

    public enum DataHolder {
        INSTANCE;

        private ArrayList<ArtikelAngebot> mObjectList;

        public static boolean hasData() {
            return INSTANCE.mObjectList != null;
        }

        public static ArrayList<ArtikelAngebot> getData() {
            final ArrayList<ArtikelAngebot> retList = INSTANCE.mObjectList;
            INSTANCE.mObjectList = null;
            return retList;
        }

        public static void setData(final ArrayList<ArtikelAngebot> objectList) {
            INSTANCE.mObjectList = objectList;
        }
    }

    public class loadAngebote extends AsyncTask<String, Void, ArrayList<ArtikelAngebot>> {

        String data = "";

        @Override
        protected ArrayList<ArtikelAngebot> doInBackground(String... params) {

            try {
                URL url = new URL("http://url/file.php");
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line = "";
                while (line != null) {
                    line = bufferedReader.readLine();
                    data = data + line;
                }
                ArrayList<String> listdata = new ArrayList<>();
                JSONArray jArray = new JSONArray(data);
                for (int i = 0; i < jArray.length(); i++) {
                    listdata.add(jArray.getString(i));
                }

                JSONArray json = new JSONArray(data);
                String[][] matrix = new String[json.length()][6];

                for (int i = 0; i < json.length(); i++) {
                    JSONObject obj = json.getJSONObject(i);
                    matrix[i][0] = String.valueOf(obj.getInt("ID"));
                    matrix[i][1] = String.valueOf(obj.getInt("art_nr"));
                    matrix[i][2] = String.valueOf(obj.getDouble("preis"));
                    matrix[i][3] = obj.getString("von");
                    matrix[i][4] = obj.getString("bis");
                    matrix[i][5] = obj.getString("art_link");
                }

                String[] all_ID = new String[matrix.length];
                String[] all_art_nr = new String[matrix.length];
                String[] all_preis = new String[matrix.length];
                String[] all_von = new String[matrix.length];
                String[] all_bis = new String[matrix.length];
                String[] all_link = new String[matrix.length];


                for (int i = 0; i < matrix.length; i++) {
                    all_ID[i] = matrix[i][0];
                    all_art_nr[i] = matrix[i][1];
                    all_preis[i] = matrix[i][2];
                    all_von[i] = matrix[i][3];
                    all_bis[i] = matrix[i][4];
                    all_link[i] = matrix[i][5];
                }

                ArrayList<ArtikelAngebot> dataList = new ArrayList<>();

                for (int i = 0; i < matrix.length; i++) {
                    ArtikelAngebot angebote = new ArtikelAngebot(all_art_nr[i], "Für: " + all_preis[i] + " €", "Von: " + all_von[i], "Bis: " + all_bis[i], all_link[i]);
                    dataList.add(angebote);
                }

                DataHolder.setData(dataList);

                return dataList;


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

            return null;
        }

        @Override
        protected void onPostExecute(ArrayList<ArtikelAngebot> QueryResult) {

            AngeboteListAdapter adapter = new AngeboteListAdapter(AngeboteActivity.this, R.layout.angebote_list_view_adapter, QueryResult);
            mListView.setAdapter(adapter);

        }
    }
}

这是您的 Utils 类

public class Utils {
    static String getLocationResultTitle(Context context, List<Location> locations) {
        if (AngeboteActivity.DataHolder.hasData()) {
            //if hasData do your stuff what you want
            String numLocationsReported = "Text1";
            return numLocationsReported + " \r\n \r\n :) \r\n \r\n" + DateFormat.getDateTimeInstance().format(new Date());

        } else {
            String numLocationsReported = "Text2";
            return numLocationsReported + " \r\n \r\n :( \r\n \r\n" + DateFormat.getDateTimeInstance().format(new Date());

        }
    }
}