android AsyncTask共享变量（全局变量）

Question

我将全局变量设置为public static int ABC;

并执行asynctask。

然后onPostExecute将ABC指定为5.现在ABC为5。

但是，UI线程没有ABC与5，只有空变量。

如何在asynctask和UI线程之间共享全局变量？

我的代码是

public class ProjectInfo extends AppCompatActivity {

private Boolean isFabOpen = false; // Fab 세팅
private FloatingActionButton fab1, fab2, fab3, fab4; // fab1 -> + , fab2 -> , fab3 -> , fab4 ->
private TextView textSubjectAdd, textSubjectCorrect, textSubjectDelete;
private Animation fab_open, fab_close, rotate_forward, rotate_backward;

private Spinner ProjectSpinner;
private ArrayList<String> SpinnerList = new ArrayList<String>();
private String SubjectName = null; // 주제 추가에 쓰이는 변수
private int flagSpinner = 0; // 주체 추가 완료를 했으면 1로 되서 Spinner을 세로 set 해준다.

// DB 관련 변수 //
private static String[] listSubjectDB; // DB의 결과를 받아오는 변수
private String[] Subjecttemp; // listDB를 <br> 단위로 끊어서 받음
private String PROJ_SEQ; // 프로젝트 SEQ를 받는다.
private static ArrayAdapter<String> Subjectadapter; // 스피너 어댑터
/**
 * ATTENTION: This was auto-generated to implement the App Indexing API.
 * See https://g.co/AppIndexing/AndroidStudio for more information.
 */
private GoogleApiClient client;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // 프로젝트 SEQ를 받아온다.
    Intent intent = getIntent();
    PROJ_SEQ = "PROJ_SEQ=" + intent.getStringExtra("PROJ_SEQ");
    new HttpTaskSubject().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
    //Log.i("testListDB" , "value:" + listSubjectDB.length);

    setContentView(R.layout.activity_projectinfo);

    // fab 관련
    textSubjectAdd = (TextView) findViewById(R.id.textSubjectAdd);
    textSubjectCorrect = (TextView) findViewById(R.id.textSubjectCorrect);
    textSubjectDelete = (TextView) findViewById(R.id.textSubjectDelete);
    fab1 = (FloatingActionButton) findViewById(R.id.fab1);
    fab2 = (FloatingActionButton) findViewById(R.id.fab2);
    fab3 = (FloatingActionButton) findViewById(R.id.fab3);
    fab4 = (FloatingActionButton) findViewById(R.id.fab4);
    fab_open = AnimationUtils.loadAnimation(getApplicationContext(), R.anim.fab_open);
    fab_close = AnimationUtils.loadAnimation(getApplicationContext(), R.anim.fab_close);
    rotate_forward = AnimationUtils.loadAnimation(getApplicationContext(), R.anim.rotate_forward);
    rotate_backward = AnimationUtils.loadAnimation(getApplicationContext(), R.anim.rotate_backward);
    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();

    // 스피너 선택 시 //
    ProjectSpinner.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Log.i("spinnervalue" , "value : " + view.getTransitionName() + " / "  + position);
        }
    });

}

public void onClickFab(View v) {
    switch (v.getId()) {
        case R.id.fab1: // fab 추가 보여주기
            animateFAB();
            break;
        case R.id.fab2: // 주제 삭제
            break;
        case R.id.fab3: // 주제 수정
            break;
        case R.id.fab4: // 주제 추가 - dialog를 통해 구현
            final EditText name = new EditText(this);
            AlertDialog.Builder alert = new AlertDialog.Builder(ProjectInfo.this);
            alert.setView(name);
            alert.setTitle("주제 추가");
            alert.setPositiveButton("추가", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    SubjectName = name.getText().toString();
                    flagSpinner = 1;
                    SpinnerAdd(); // 주제 추가 완료 버튼을 누르면 spinner 새로 set
                }
            });

            alert.setNegativeButton("취소", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    dialog.dismiss(); // 닫기
                    flagSpinner = 0;
                }
            });

            alert.show();
            break;
    }
}

// FAB 애니메이션 효과
public void animateFAB() {
    if (isFabOpen) {
        fab1.startAnimation(rotate_backward);
        textSubjectAdd.startAnimation(fab_close);
        textSubjectCorrect.startAnimation(fab_close);
        textSubjectDelete.startAnimation(fab_close);
        fab2.startAnimation(fab_close);
        fab3.startAnimation(fab_close);
        fab4.startAnimation(fab_close);
        fab2.setClickable(false);
        fab3.setClickable(false);
        fab4.setClickable(false);
        isFabOpen = false;
        Log.d("Raj", "close");
    } else {
        fab1.startAnimation(rotate_forward);
        textSubjectAdd.startAnimation(fab_open);
        textSubjectCorrect.startAnimation(fab_open);
        textSubjectDelete.startAnimation(fab_open);
        fab2.startAnimation(fab_open);
        fab3.startAnimation(fab_open);
        fab4.startAnimation(fab_open);
        fab2.setClickable(true);
        fab3.setClickable(true);
        fab4.setClickable(true);
        isFabOpen = true;
        Log.d("Raj", "open");
    }
}

// 주제 추가 완료시 (flag == 1 이면 spinner 새로 추가 )
public void SpinnerAdd() {
    if (flagSpinner == 1) {
        SpinnerList.add(SubjectName);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item, SpinnerList);
        ProjectSpinner.setAdapter(adapter);

        // DB에 추가된 주자를 insert 한다. //

    } else {
        return;
    }

}

/**
 * ATTENTION: This was auto-generated to implement the App Indexing API.
 * See https://g.co/AppIndexing/AndroidStudio for more information.
 */
public Action getIndexApiAction() {
    Thing object = new Thing.Builder()
            .setName("ProjectInfo Page") // TODO: Define a title for the content shown.
            // TODO: Make sure this auto-generated URL is correct.
            .setUrl(Uri.parse("http://[ENTER-YOUR-URL-HERE]"))
            .build();
    return new Action.Builder(Action.TYPE_VIEW)
            .setObject(object)
            .setActionStatus(Action.STATUS_TYPE_COMPLETED)
            .build();
}

@Override
public void onStart() {
    super.onStart();

    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    client.connect();
    AppIndex.AppIndexApi.start(client, getIndexApiAction());
}

@Override
public void onStop() {
    super.onStop();

    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    AppIndex.AppIndexApi.end(client, getIndexApiAction());
    client.disconnect();
}

// PHP 검색 쿼리 보내는 class
public class HttpTaskSubject extends AsyncTask<String, Void, String> {
    /* Bitmap bitmap , String image는 전역변수 */
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub
        try {

            String urlPath = "http://58.142.149.131/grad/Grad_project_list_subject.php";

            // 내가 보낼 데이터 (쿼리, SUBSEQ 전역변수, switch 에서 정해준다.)
            String data = PROJ_SEQ;

            URL url = new URL(urlPath);
            URLConnection conn = url.openConnection();
            conn.setDoOutput(true);
            OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());

            //추가 할 내용 - 서버 on/off 검사

            // 문자열 전송
            wr.write(data);
            wr.flush();

            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

            StringBuilder sb = new StringBuilder();
            String CheckNull = "0";
            String line = null;

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

            CheckNull = sb.toString();

            if (sb.toString() != "") {
                listSubjectDB = sb.toString().split("<br>");
                return sb.toString();
            } else {
                return null;
            }

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        //오류시 null 반환
        return null;
    }

    //asyonTask 3번째 인자와 일치 매개변수값 -> doInBackground 리턴값이 전달됨
    //AsynoTask 는 preExcute - doInBackground - postExecute 순으로 자동으로 실행됩니다.
    //ui는 여기서 변경
    protected void onPostExecute(String value) { // 스피너 불러오기

        ProjectSpinner = (Spinner) findViewById(R.id.ProjectSpinner);
        Subjectadapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.support_simple_spinner_dropdown_item, SpinnerList);
        for (int i = 1; i < listSubjectDB.length; i++) {
            Subjecttemp = split(listSubjectDB[i]); // seq / 주제 <BR>
            Subjectadapter.add(Subjecttemp[1]);
        }
        ProjectSpinner.setAdapter(Subjectadapter);
        PROJ_SEQ = null;

        super.onPostExecute(value);
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }
}

// PHP DB insert 쿼리를 보내는 class (주제추가)
public class HttpTaskSubjectAdd extends AsyncTask<String, Void, String> {
    /* Bitmap bitmap , String image는 전역변수 */
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub
        try {

            String urlPath = "http://58.142.149.131/grad/Grad_project_list_subject.php";

            // 내가 보낼 데이터 (쿼리, SUBSEQ 전역변수, switch 에서 정해준다.)
            String data = "ADD";

            URL url = new URL(urlPath);
            URLConnection conn = url.openConnection();
            conn.setDoOutput(true);
            OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());

            //추가 할 내용 - 서버 on/off 검사

            // 문자열 전송
            wr.write(data);
            wr.flush();

            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

            StringBuilder sb = new StringBuilder();
            String CheckNull = "0";
            String line = null;

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

            CheckNull = sb.toString();

            if (sb.toString() != "") {
                listSubjectDB = sb.toString().split("<br>");
                return sb.toString();
            } else {
                return null;
            }

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        //오류시 null 반환
        return null;
    }

    //asyonTask 3번째 인자와 일치 매개변수값 -> doInBackground 리턴값이 전달됨
    //AsynoTask 는 preExcute - doInBackground - postExecute 순으로 자동으로 실행됩니다.
    //ui는 여기서 변경
    protected void onPostExecute(String value) { // 스피너 불러오기

        ProjectSpinner = (Spinner) findViewById(R.id.ProjectSpinner);
        Subjectadapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.support_simple_spinner_dropdown_item, SpinnerList);
        for (int i = 1; i < listSubjectDB.length; i++) {
            Subjecttemp = split(listSubjectDB[i]); // seq / 주제 <BR>
            Subjectadapter.add(Subjecttemp[1]);
        }
        ProjectSpinner.setAdapter(Subjectadapter);
        PROJ_SEQ = null;
        super.onPostExecute(value);
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }
}

// PHP 주제에 해당하는 파일 불러오는 통신 class
public class HttpTaskSubjectShow extends AsyncTask<String, Void, String> {
    /* Bitmap bitmap , String image는 전역변수 */
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub
        try {

            String urlPath = "http://58.142.149.131/grad/Grad_project_list_subject.php";

            // 내가 보낼 데이터 (쿼리, SUBSEQ 전역변수, switch 에서 정해준다.)
            String data = "ADD";

            URL url = new URL(urlPath);
            URLConnection conn = url.openConnection();
            conn.setDoOutput(true);
            OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());

            //추가 할 내용 - 서버 on/off 검사

            // 문자열 전송
            wr.write(data);
            wr.flush();

            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

            StringBuilder sb = new StringBuilder();
            String CheckNull = "0";
            String line = null;

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

            CheckNull = sb.toString();

            if (sb.toString() != "") {
                listSubjectDB = sb.toString().split("<br>");
                return sb.toString();
            } else {
                return null;
            }

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        //오류시 null 반환
        return null;
    }

    //asyonTask 3번째 인자와 일치 매개변수값 -> doInBackground 리턴값이 전달됨
    //AsynoTask 는 preExcute - doInBackground - postExecute 순으로 자동으로 실행됩니다.
    //ui는 여기서 변경
    protected void onPostExecute(String value) { // 스피너 불러오기

        ProjectSpinner = (Spinner) findViewById(R.id.ProjectSpinner);
        Subjectadapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.support_simple_spinner_dropdown_item, SpinnerList);
        for (int i = 1; i < listSubjectDB.length; i++) {
            Subjecttemp = split(listSubjectDB[i]); // seq / 주제 <BR>
            Subjectadapter.add(Subjecttemp[1]);
        }
        ProjectSpinner.setAdapter(Subjectadapter);
        PROJ_SEQ = null;
        super.onPostExecute(value);
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }
}

// listDB를 #단위로 끊어서 반환
public String[] split(String temp123) {
    String[] temp2 = temp123.split("#");
    return temp2;
  }
}

我希望ProjectSpinner在UI线程上工作......但是为null。

Answer 1

AsyncTask是后台流程，如果您这样做

// background process started
new AsncTaskClass.execute();
//you are getting value from static variable,
//this line will be executed immediately after execute `AsyncTask` it will not wait while finish so you will get `null` value 
String value = AsncTaskClass.ABC;

对于你的解决方案，你必须在postExecute后使用abstract或interface来获取值，参见例：

  

AsyncTask类

public abstract class DemoAsync extends AsyncTask<Void, Void, Void> {
@Override
    protected Void doInBackground(Void... voids){
        return null;
    }
@Override
    protected void onPostExecute(Void result) {
         onGetValue(pass value here);
    }

     public abstract void onGetValue(String value);//Create an `abstract` method in AsyncTask class

    }

  

现在像你一样打电话给上课

 new DemoAsync() {
     @Override
     public void onGetValue(String value) {
            //you will get this implemented method 
            // TO do something here, hurray you got value!
     }
 }.execute();

Answer 2

我发布下面的示例代码，请阅读并试试。

＆＃13;

＆＃13;

public class MainActivity extends AppCompatActivity {

    static String globalString;
    TextView hello;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        hello = (TextView) findViewById(R.id.textView1);
        new asyncclass().execute("");
    }
    private class asyncclass extends AsyncTask<String,String,String>{
        @Override
        protected String doInBackground(String... params) {
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return "New message for Hello word";

        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            globalString = s;
            hello.setText(globalString);
        }
    }
}

＆＃13;

＆＃13;

＆＃13;