如何等待Android UI線程中異步填充的對象而不阻止它？

Question

我有一個人來處理實體Profilo（配置文件）的注冊和刪除。

通過傳遞標識符並以異步方式在服務器上收集信息來設置此實體。

我的問題是，當必須返回仍未加載的profilo實例時，它將返回null。

public class AccountHandler {
    private static AccountHandler istanza = null;

    Context context;
    private boolean logged;
    private Profilo profilo;


    private AccountHandler(Context context) {
        this.context = context;
        //initialization
        //setting logged properly
            assignField(this.getName());
        }
    }

    public static AccountHandler getAccountHandler(Context context) {
        if (istanza == null) {
            synchronized (AccountHandler.class) {
                if (istanza == null) {
                    istanza = new AccountHandler(context);
                }
            }
        }
        return istanza;
    }

    public void setAccount(String nickname, String accessingCode) {
        logged = true;
        assignField(nickname);
    }

    //other methods

    private void assignField(String nickname) {
        ProfiloClient profiloClient = new ProfiloClient();
        profiloClient.addParam(Profilo.FIELDS[0], nickname);
        profiloClient.get(new JsonHttpResponseHandler() {
            @Override
            public void onSuccess(int statusCode,
                                  Header[] headers,
                                  JSONArray response) {
                JSONObject objson = null;
                try {
                    objson = (JSONObject) response.getJSONObject(0);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
                AccountHandler accountHandler = AccountHandler.getAccountHandler(context);
    // Profilo is created with a JSONObject
    // **setProfilo is called in async**
                **accountHandler.setProfilo(new Profilo(objson));**
            }

        });
    }


    private void setProfilo(Profilo profilo) {
        this.profilo = profilo;
    }



    public Profilo getProfilo() {
        if( logged && profilo == null)
            //How can I wait that profilo is loaded by the JsonHttpResponseHandler before to return it

        return this.profilo;
    }


}

Answer 1

除了調用getProfilo您可以使用一種回調機制，在該機制中， AccountHandler類在加載配置文件時通知調用方。 例如

  public void setAccount(String nickname, String accessingCode, MyCallback cb) {
      assignField(nickname, cb);
  }
  private void assignField(String nickname, MyCallback cb) {
      ....
      accountHandler.setProfilo(new Profilo(objson));
      cb.onSuccess(this.profilo);
  }

在AccountHandler類中創建一個內部接口MyCallback （重命名）

public class AccountHandler {
    public interface MyCallback {
        void onSuccess(Profilo profile);
    }
}

現在，無論何時調用setAccount您都將傳遞回調並在配置文件可用時得到通知，例如

accountHandler.setAccount("Test", "Test", new AccountHandler.MyCallback() {
        void onSuccess(Profilio profile) {
            // do something with the profile
        }
    }

Answer 2

正如@Murat K.所建議的那樣，我添加了我的類的接口，該接口將提供一種可以隨時使用的對象調用方法。

   public class AccountHandler {

    public interface Callback {
            void profiloReady(Profilo profilo);
    }
}

在處理程序中的getProfilo中調用此方法，該處理程序對getProfilo進行遞歸調用，直到准備使用profilo為止，然后調用該回調方法，該類作為getProfilo的參數傳遞。

public void getProfilo(final Callback Callback) {
    if( logged && (profilo == null || !profilo.isReady() ) {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                getProfilo(Callback);
            }
        }, 500);
    }else
        Callback.profiloReady(profilo);
}

getProfilo調用示例

public class ProfiloCall implements AccountHandler.MyCallback {

        @Override
        public void profiloReady(Profilo profilo) {
            //Use profilo as needed
            //EXECUTED ONLY WHEN PROFILO IS READY
        }


        public void callerMethod() {
            //useful code
            accountHandler.getProfilo(this);
            //other useful code

        }
    }