android - 多个 Java fragment 使用的 Asynctask

Question

我目前正在开发一个项目，我在 Android 上从 JSON 转储中获取数据。到目前为止，我是否在每个 fragment 中都设置了自定义的 Asynctask，我需要在其中从 JSON 转储中获取数据。我很好奇的是我是否可以拥有一个公共(public) Java 类， fragment 可以在需要获取数据时“使用”它。

这是我尝试执行此操作的示例。首先是从公共(public) java 类调用 Asynctask 的 fragment :

public class DataTabelFragment extends Fragment {

private TextView sensor1;
private Button jsonButton;

jsonAsynctask jsonasynctask = new jsonAsynctask();


public DataTabelFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate( R.layout.fragment_data_tabel, container, false );

    sensor1 = (TextView) view.findViewById( R.id.sensor1Box );
    //jsonButton = (Button) view.findViewById( R.id.buttonjson );

    new jsonAsynctask().execute();

    for (int i = 0; i < jsonasynctask.allId.size(); i++) {
        sensor1.append( jsonasynctask.allId.get( i ) + " | " + jsonasynctask.allDevice.get( i ) + " | " + jsonasynctask.allTemp.get( i ) + " | " + jsonasynctask.allHum.get( i ) + " | " + jsonasynctask.allBat.get( i ) + " | " + jsonasynctask.allMode.get( i ) + " | " + jsonasynctask.allLux.get( i ) + " | " + jsonasynctask.allDate_time.get( i ) + "\n\n" );

    }

    //new jsonConnection().execute();

    /*

    jsonButton.setOnClickListener( new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            new jsonConnection().execute();
        }
    } );*/



    return view;

}


}

这是带有 Asynctask 的 java 类:

public class jsonAsynctask extends MainActivity {

private TextView sensor1;
private Button jsonButton;

JSONObject deviceArray;
JSONObject tempArray;
JSONObject humArray;
JSONObject batArray;
JSONObject modeArray;
JSONObject date_timeArray;
JSONObject luxArray;

JSONArray json2;

List<String> allId = new ArrayList<String>();
List<String> allDevice = new ArrayList<String>();
List<String> allTemp = new ArrayList<String>();
List<String> allHum = new ArrayList<String>();
List<String> allBat = new ArrayList<String>();
List<String> allMode = new ArrayList<String>();
List<String> allDate_time = new ArrayList<String>();
List<String> allLux = new ArrayList<String>();

String basicAuth;
String line;
String json_string;
String json;
String cxwebURL;
String credentials;
String password;
String username;

Gson gson;
ProgressDialog pd;
String data = "";
HttpURLConnection connection;
BufferedReader bufferedReader;

String id = "";
JSONObject idArray;

URL url;

private static String encodeBase64URLSafeString(byte[] binaryData) {

    return android.util.Base64.encodeToString( binaryData, android.util.Base64.URL_SAFE );

}

public class jsonConnection extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... voids) {

        username = "xxx";

        password = "xxx";

        credentials = username + ":" + password;

        cxwebURL = "https://" + credentials + "@xxx.com/fetch.php?device=xxx";

        try {

            url = new URL( cxwebURL );

            connection = (HttpsURLConnection) url.openConnection();

            basicAuth = "Basic " + new String( encodeBase64URLSafeString( credentials.getBytes() ) );

            connection.setRequestProperty( "Authorization", basicAuth );
            connection.setRequestMethod( "GET" );
            connection.setRequestProperty( "Content-Type", "application/x-www-form-urlencoded" );
            connection.setRequestProperty( "Content-Language", "en-US" );
            connection.setUseCaches( false );
            connection.setDoInput( true );
            connection.setDoOutput( true );
            connection.connect();

            InputStream stream = connection.getInputStream();

            bufferedReader = new BufferedReader( new InputStreamReader( stream ) );

            line = "";

            while (line != null) {
                line = bufferedReader.readLine();
                data = data + line;
            }

            json2 = new JSONArray( data );

            for (int i = 0; i < json2.length(); i++) {
                idArray = json2.getJSONObject( i );
                deviceArray = json2.getJSONObject( i );
                tempArray = json2.getJSONObject( i );
                humArray = json2.getJSONObject( i );
                batArray = json2.getJSONObject( i );
                modeArray = json2.getJSONObject( i );
                date_timeArray = json2.getJSONObject( i );
                luxArray = json2.getJSONObject( i );
                id = idArray.getString( "id" );

                String temp = tempArray.getString( "temp" );
                String device = deviceArray.getString( "device" );

                String hum = humArray.getString( "hum" );

                String bat = batArray.getString( "bat" );

                String mode = modeArray.getString( "mode" );

                String date_time = date_timeArray.getString( "time" );

                String lux = luxArray.getString( "light" );

                allId.add( id );
                allDevice.add( device );
                allTemp.add( temp );
                allHum.add( hum );
                allBat.add( bat );
                allMode.add( mode );
                allDate_time.add( date_time );
                allLux.add( lux );


            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        pd = new ProgressDialog( new MainActivity() );
        pd.setMessage( "Være sød at vente" );
        //pd.setCancelable( false );
        pd.show();
    }

    @Override
    public void onPostExecute(Void result) {
        super.onPostExecute( result );
        if (pd.isShowing()) {
            pd.dismiss();
        }

        System.out.println( data );

        gson = new Gson();

        json = gson.toJson( data );

        System.out.println( "String json: " + json );

        json_string = data;

        System.out.println( "json_string: " + json_string );

//            System.out.println( "DET HER ER ID!!: " + allId.get( 1 ) );

        //textView2.setMovementMethod( new ScrollingMovementMethod() );


        System.out.println("Size of Array: " + allId.size());



    }
        }


}

我能像这样编程吗，还是我应该继续在每个 fragment 中有一个 Asynctask？顺便说一下，“新的 jsonAsynctask().execute();”在 fragment 中不起作用，我收到此错误:

error: cannot find symbol class execute

* 更新 *

这是 Asynctask 所在的 Java 类中的更新。

public class jsonAsynctask extends AsyncTask<Void, Void, Void> {

private TextView sensor1;
private Button jsonButton;

JSONObject deviceArray;
JSONObject tempArray;
JSONObject humArray;
JSONObject batArray;
JSONObject modeArray;
JSONObject date_timeArray;
JSONObject luxArray;

JSONArray json2;

List<String> allId = new ArrayList<String>();
List<String> allDevice = new ArrayList<String>();
List<String> allTemp = new ArrayList<String>();
List<String> allHum = new ArrayList<String>();
List<String> allBat = new ArrayList<String>();
List<String> allMode = new ArrayList<String>();
List<String> allDate_time = new ArrayList<String>();
List<String> allLux = new ArrayList<String>();

String basicAuth;
String line;
String json_string;
String json;
String cxwebURL;
String credentials;
String password;
String username;

Gson gson;
ProgressDialog pd;
String data = "";
HttpURLConnection connection;
BufferedReader bufferedReader;

String id = "";
JSONObject idArray;

URL url;

private static String encodeBase64URLSafeString(byte[] binaryData) {

    return android.util.Base64.encodeToString( binaryData, android.util.Base64.URL_SAFE );

}

    @Override
    protected Void doInBackground(Void... voids) {

        username = "xxx";

        password = "xxx";

        credentials = username + ":" + password;

        cxwebURL = "https://" + credentials + "@xxx.com/fetch.php?device=xxx";


        try {

            url = new URL( cxwebURL );

            connection = (HttpsURLConnection) url.openConnection();

            basicAuth = "Basic " + new String( encodeBase64URLSafeString( credentials.getBytes() ) );

            connection.setRequestProperty( "Authorization", basicAuth );
            connection.setRequestMethod( "GET" );
            connection.setRequestProperty( "Content-Type", "application/x-www-form-urlencoded" );
            connection.setRequestProperty( "Content-Language", "en-US" );
            connection.setUseCaches( false );
            connection.setDoInput( true );
            connection.setDoOutput( true );
            connection.connect();

            InputStream stream = connection.getInputStream();

            bufferedReader = new BufferedReader( new InputStreamReader( stream ) );

            line = "";

            while (line != null) {
                line = bufferedReader.readLine();
                data = data + line;
            }

            json2 = new JSONArray( data );


            for (int i = 0; i < json2.length(); i++) {
                idArray = json2.getJSONObject( i );
                deviceArray = json2.getJSONObject( i );
                tempArray = json2.getJSONObject( i );
                humArray = json2.getJSONObject( i );
                batArray = json2.getJSONObject( i );
                modeArray = json2.getJSONObject( i );
                date_timeArray = json2.getJSONObject( i );
                luxArray = json2.getJSONObject( i );
                id = idArray.getString( "id" );

                String temp = tempArray.getString( "temp" );

                String device = deviceArray.getString( "device" );


                String hum = humArray.getString( "hum" );

                String bat = batArray.getString( "bat" );

                String mode = modeArray.getString( "mode" );

                String date_time = date_timeArray.getString( "time" );

                String lux = luxArray.getString( "light" );

                allId.add( id );
                allDevice.add( device );
                allTemp.add( temp );
                allHum.add( hum );
                allBat.add( bat );
                allMode.add( mode );
                allDate_time.add( date_time );
                allLux.add( lux );


            }


        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        pd = new ProgressDialog( new MainActivity() );
        pd.setMessage( "Være sød at vente" );
        pd.show();
    }

    @Override
    public void onPostExecute(Void result) {
        super.onPostExecute( result );
        if (pd.isShowing()) {
            pd.dismiss();
        }

        gson = new Gson();

        json = gson.toJson( data );

        json_string = data;


      }
        }

}

我收到的错误:

error: class, interface, or enum expected

感谢您的帮助!提前致谢。

Answer 1

为 AsyncTask 创建单独的类比在每个 fragment 中创建 AsyncTask 更好。你收到错误是因为在 new jsonAsynctask().execute()//jsonAsyncTask 扩展自 MainActivity，因此它不是 AsyncTask

用新的 jsonConnection .execute() 替换上面的行