我有一个应用程序，它在遍历文件系统时递归地创建 Activity 的多个实例(每个文件夹一个 Activity )。在 Activity 堆栈中向前移动时(即正常文件夹遍历)，我通过 Intent 检索数据。当我从父文件夹转到子文件夹时，应用程序运行良好。我在[返回]时遇到问题，因为文件/文件夹列表与之前的 Activity ( child )保持不变。我不想再次从 Internet 检索文件夹数据，所以可以跟踪以前的 Activity 状态吗？这是我的 Activity 的一段代码。谢谢

public class RisorseActivity extends DashboardActivity implements Observer {
private Docente docente;
private String get_response;
private String response;
//private HttpsClient client;

private ListView list;
private RelativeLayout progressLayout;
private ProgressBar progressBar;
private TextView txtMateriale;

private ArrayList<Risorsa> risorseList;
private RisorseAdapter risAdapter;
private RisorseList risList;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_risorse);
    setTitleFromActivityLabel(R.id.title_text);

    list = (ListView) findViewById(R.id.ListRisorse);
    list.setClickable(true);


    Intent intent = getIntent();
    // vengono recuperati i parametri dalla activity chiamante
    docente = (Docente) intent.getSerializableExtra(getPackageName() + ".Docente");
    //cartella = (Insegnamento) intent.getSerializableExtra(pkg + ".Insegnamento");
    get_response = intent.getExtras().getString("get_response");
    response = intent.getExtras().getString("response");

    list.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> arg0, View view,
                int position, long index) {
            if (risorseList.get(position).getType().equalsIgnoreCase("Folder")) {
                Intent intRisorse = new Intent(getApplicationContext(), RisorseActivity.class);
                intRisorse.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
                intRisorse.putExtra(getPackageName() + ".Docente", docente);
                intRisorse.putExtra("get_response", risorseList.get(position).getURL()); 
                startActivity(intRisorse);
            } else if (risorseList.get(position).getType().equalsIgnoreCase("File")) {
                //--------------- DOWNLOAD DEL FILE-------------------
            }
        }
    });


    startRisorseService();
}


// Aggiorna la View della Activity popolando la lista dei docenti trovati
private void updateView() {

    this.risAdapter = new RisorseAdapter(this, this.risorseList);
    if (this.risAdapter != null) {
        this.list.setAdapter(this.risAdapter);

    } else {
        Toast.makeText(this, "Errore caricamento lista materiale",
                Toast.LENGTH_LONG).show();
    }
}

private void startRisorseService() {
    // risList conterrà il nostro modello dei dati (l'array di oggetti
    // Ricevimento)
    risList = RisorseList.getInstance();
    if (risList.countObservers() == 0)
        risList.addObserver(this); // aggiungiamo la nostra "View" come
                                    // osservatore del modello dati

    loginState = ((LoginState) getApplicationContext());

    Handler handler = new RisorseHandler();
            //IT IS THE TASK THATH RETRIEVE THE DATA
    RisorseService task = null;
    if (response != null){
        task = new RisorseService(handler, loginState, response);
    }else
        task = new RisorseService(handler, loginState);
    if (task != null)
        task.execute(get_response);
}

public void update(Observable observable, Object arg1) {
    if(observable instanceof RisorseList){ 
        // in quanto potremmo avere piu modelli dati
        // verifichiamo su quale modello è avvenuto un cambiamento dei dati
        // prima di effettuare il cast
        this.risorseList = ((RisorseList) observable).getData();
    }
            updateView();
    risList.deleteObserver(this);
}

public void onClickRefresh(View v) {
    startRisorseService();
}


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

            // IF I UNCOMMENT THESE LINES IT WORK BUT RETRIEVE DATA FROM INTERNET AGAIN!!!
    /*if (risAdapter == null)
        startRisorseService();
    else{
        risAdapter.notifyDataSetChanged();

    }*/
    if (risAdapter != null)
    updateView();
}

最佳答案

这不会回答您的问题，但您是否考虑过使用 Fragments而不是每次都创建一个新 Activity ？

想法是，您将在 Fragment 中显示列表项，而不是每次打开文件夹时都重新创建 RisorseActivity，您将替换旧 fragment 与新的。

此外，在提交 fragment 之前，您将调用 addToBackStack()，以便将事务添加到 fragment 事务的后栈中。此返回堆栈由 Activity 管理，并允许用户通过按“返回”按钮返回到前一个 fragment 状态。

这样，当你返回时，堆栈中的前一个 fragment 会弹出，并且不会再次下载数据。

关于android - 返回递归 Activity (类似文件系统)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8279709/