Question

我目前有两个活动在做HTTP请求。在第二个活动上，有一个前一个按钮。我希望能够在不丢失信息的情况下重新开始第一项活动，因为目前我丢失了所有已恢复的信息。

第一项活动：

public class GetChildrenList extends AppCompatActivity implements View.OnClickListener {
private ArrayList<Child> childrenImeList = new ArrayList<Child>();

private ListView itemsListView;
private TextView tv_signin_success;

String email;
String password;

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

    String infos_user = (String) getIntent().getSerializableExtra("infos_user");

    tv_signin_success = (TextView) findViewById(R.id.tv_signin_success);


    tv_signin_success.setText("Bonjour " + infos_user + "!");

    itemsListView  = (ListView)findViewById(R.id.list_view_children);


    new GetChildrenAsync().execute();
}

class GetChildrenAsync extends AsyncTask<String, Void, ArrayList<Child>>  {

    private Dialog loadingDialog;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        loadingDialog = ProgressDialog.show(GetChildrenList.this, "Please wait", "Loading...");
    }

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

        InputStream is = null;

        int statusCode = 0;
        int id = 0;
        int age = 0;
        email = (String) getIntent().getSerializableExtra("email");
        password = (String) getIntent().getSerializableExtra("password");
        String result = null;
        String first_name = null;
        String last_name = null;


        try {
            //Http request to communicate with our system
            HttpClient httpClient = new DefaultHttpClient();

            HttpGet httpGet = new HttpGet();
            URI website = new URI("http://192.168.1.33:5000/childrenime/list");
            httpGet.setURI(website);

            String base64EncodedCredentials = Base64.encodeToString(
                    (email + ":" + password).getBytes(),
                    Base64.NO_WRAP);

            httpGet.setHeader("Authorization", "Basic " + base64EncodedCredentials);

            HttpResponse response = httpClient.execute(httpGet);

            statusCode = response.getStatusLine().getStatusCode();

            HttpEntity entity = response.getEntity();
            is = entity.getContent();

            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 8);
            StringBuilder sb = new StringBuilder();

            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            result = sb.toString();
            String jsonResult = "{ \"children\":" + result + "}";

            Log.d("result1", jsonResult);

            //Manage JSON result
            JSONObject jsonObject = new JSONObject(jsonResult);
            JSONArray childrenArray = jsonObject.getJSONArray("children");

            for (int i = 0; i < childrenArray.length(); ++i) {
                JSONObject child = childrenArray.getJSONObject(i);
                id = child.getInt("id");
                first_name = child.getString("first_name");
                last_name = child.getString("last_name");
                age = child.getInt("age");

                String name = first_name + " " + last_name;

                childrenImeList.add(new Child(id,name,age));
            }

        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }

        return childrenImeList;

    }

    @Override
    protected void onPostExecute(final ArrayList<Child> childrenListInformation) {
        loadingDialog.dismiss();
        CustomListChildrenAdapter adapter = new CustomListChildrenAdapter(GetChildrenList.this, childrenListInformation);
        itemsListView.setAdapter(adapter);
    }
  }
}

第二项活动：

public class GetLearningGoalsList extends AppCompatActivity implements View.OnClickListener {
private ArrayList<LearningGoal> childrenLearningList = new ArrayList<LearningGoal>();

private Button btn_previous;
private ListView itemsListView;

String email;
String password;

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

    btn_previous = (Button) findViewById(R.id.btn_previous);

    btn_previous.setOnClickListener(this);

    itemsListView  = (ListView)findViewById(R.id.list_view_learning_goals);


    new GetLearningGoalsAsync().execute();
}

@Override
public void onClick(View v) {
    Intent myIntent = new Intent(GetLearningGoalsList.this, GetChildrenList.class);
    myIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(myIntent);
    finish();
    return;
}

class GetLearningGoalsAsync extends AsyncTask<String, Void, ArrayList<LearningGoal>>  {

    private Dialog loadingDialog;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        loadingDialog = ProgressDialog.show(GetLearningGoalsList.this, "Please wait", "Loading...");
    }

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

        InputStream is = null;

        int statusCode = 0;
        int id = 0;
        email = (String) getIntent().getSerializableExtra("email");
        password = (String) getIntent().getSerializableExtra("password");
        int idChild = (int) getIntent().getSerializableExtra("idChild");
        String json = null;
        String result = null;
        String name = null;
        String start_date = null;
        String end_date = null;

        try {
            //Http request to communicate with our system
            HttpClient httpClient = new DefaultHttpClient();

            HttpPost httpPost = new HttpPost();
            URI website = new URI("http://192.168.1.33:5000/learningchild/list");
            httpPost.setURI(website);

            JSONObject jsonObj = new JSONObject();
            jsonObj.accumulate("idChild", idChild);

            json = jsonObj.toString();

            StringEntity se = new StringEntity(json);

            httpPost.setEntity(se);

            String base64EncodedCredentials = Base64.encodeToString(
                    (email + ":" + password).getBytes(),
                    Base64.NO_WRAP);

            httpPost.setHeader("Authorization", "Basic " + base64EncodedCredentials);
            httpPost.setHeader("Accept", "application/json");
            httpPost.setHeader("Content-type", "application/json");

            HttpResponse response = httpClient.execute(httpPost);

            statusCode = response.getStatusLine().getStatusCode();

            HttpEntity entity = response.getEntity();
            is = entity.getContent();

            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 8);
            StringBuilder sb = new StringBuilder();

            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            result = sb.toString();
            String jsonResult = "{ \"learningGoals\":" + result + "}";

            Log.d("result1", jsonResult);

            //Manage JSON result
            JSONObject jsonObject = new JSONObject(jsonResult);
            JSONArray learningGoalsArray = jsonObject.getJSONArray("learningGoals");

            for (int i = 0; i < learningGoalsArray.length(); ++i) {
                JSONObject learningGoal = learningGoalsArray.getJSONObject(i);
                id = learningGoal.getInt("id");
                name = learningGoal.getString("name");
                start_date = learningGoal.getString("start_date");
                end_date = learningGoal.getString("end_date");


                childrenLearningList.add(new LearningGoal(id,name,start_date,end_date));
            }

        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }

        return childrenLearningList;

    }

    @Override
    protected void onPostExecute(final ArrayList<LearningGoal> learningListInformation) {
        loadingDialog.dismiss();
        CustomListLearningGoalAdapter adapter = new CustomListLearningGoalAdapter(GetLearningGoalsList.this, learningListInformation);
        itemsListView.setAdapter(adapter);
    }
  }
}

我怎能这样做，以免丢失信息？

谢谢。

Answer 1

您可以使用SharedPreferences保存数据。

首先，在第二个活动上创建SharedPreferences：

SharedPreferences pref = getApplicationContext()
    .getSharedPreferences("MyPreferences", MODE_PRIVATE); 
Editor editor = pref.edit();

然后将您的数据存储为KEY/VALUE对：

editor.putString("key", "string value");
editor.commit();

然后获取第一项活动的数据：

SharedPreferences sharedPreferences = 
    PreferenceManager.getDefaultSharedPreferences(this);
String value = mSharedPreference.getString("key", "");

在Android Example上，您可以遵循一些SharedPreferences基础知识。

Answer 2

嗯，首先要知道的是，有几种方法可以保留信息，这取决于具体内容和方式。

可以通过覆盖“onSaveInstanceState”方法来保存数据以保存数据：

@Override
protected void onSaveInstanceState(Bundle iOutState)
{
    super.onSaveInstanceState(iOutState);

    iOutState.putString("USER_INFORMATION", infos_user);
    iOutState.putInt("CHILD_ID", idChild);
}

并覆盖“onRestoreInstanceState”方法以加载保存的数据：

@Override
protected void onRestoreInstanceState(Bundle iSavedInstanceState)
{
    super.onRestoreInstanceState(iSavedInstanceState);
    infos_user = iSavedInstanceState.getString("USER_INFORMATION");
    idChild = iSavedInstanceState.getInt("CHILD_ID");
}

因此，当活动状态发生变化时，它会保存变量的最后值，并在必要时恢复它们。

数据可以保存为单身。
可以使用SharedPreferences或SQLite DB

此外，您没有提供足够的信息，但如果我理解正确，您首先调用“GetChildrenList”活动，然后“GetLearningGoalsList”，最后您单击上一个按钮返回“GetChildrenList”。 IF 就是这种情况，您需要了解默认情况下，活动不像单个实体那样作为单个实体运行，而是在每个“startActivity”调用中创建。换句话说，每次调用“startActivity”命令时，都会创建一个全新的活动，因此最终会有3个活动;类“GetChildrenList”中的2个和“GetLearningGoalsList”中的一个。要解决这个问题：

按下上一个按钮时调用“onBackPressed”方法。
将“GetChildrenList”启动模式设置为“singleInstance”。可以在清单中或作为用于启动活动的意图中的标志来完成。除“singleInstance”之外，还有几种类型的启动模式。可以找到更多信息here。

祝你好运=）

返回上一个活动

2 个答案: