重新创建 Activity 后，Android Volley 不会从服务器加载数据

Question

我有一个大问题困扰了我几天。在我正在处理的应用程序中，我有几个 Activity ，其中一个是中央 (BaseActivity)，应用程序从中转到其他 Activity ，并且在每个 Activity 中，它都与 Volley 库一起从 API 获取数据。

例如，如果我从 BaseActivity 转到 SelectionActivity，在 SelectionActivity 中我会收到包含所有必要数据的回收 View 。这很好，这就是我需要的。

但是，当我通过单击工具栏上的后退按钮或主页按钮完成 Activity ，然后想再次返回到 SelectionActivity 时，数据不会再次加载。它没有说明任何异常，只是不加载任何内容。

我一直在 Internet 上搜索，但似乎找不到解决方案。

编辑:当我使用调试器进行调查时，可以进一步确定。似乎一切都应该有效，因为它通过了响应，并通过了一切。但是，我没有看到任何东西，而不是充满数据的 RecyclerView。

选择 Controller 方法:

public void getAllJobs()
{
    queue = VolleyRequestHandler.getInstance(false).getQueue();

    JsonArrayRequest jobsRequest = new JsonArrayRequest(Request.Method.GET,makeAllJobsRequest(),
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    List<Job> jobs = new ArrayList<>();
                    Job job;
                    try
                    {
                        for (int i=0; i<response.length(); i++)
                        {
                            JSONObject dbJob = response.getJSONObject(i);
                            job = new Job();

                            job.setId(dbJob.getLong("JobId"));
                            job.setName(dbJob.getString("JobText"));
                            job.setCustName(dbJob.getString("CustomerName"));

                            jobs.add(job);
                        }

                        // Entries are being sorted!
                        Collections.sort(jobs, new CustomerComparator());

                        injection.onGettingAllJobs(jobs);
                    }
                    catch (JSONException e)
                    {
                        e.printStackTrace();
                        injection.onErrorSelection(e.getMessage());
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            injection.onErrorSelection(error.getMessage());
        }
    });

    jobsRequest.setTag(injection.GET_JOBS_TAG);

    jobsRequest.setRetryPolicy(new DefaultRetryPolicy(
            (int) TimeUnit.SECONDS.toMillis(10),//time out in 10second
            DefaultRetryPolicy.DEFAULT_MAX_RETRIES,//DEFAULT_MAX_RETRIES = 1;
            DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

    queue.add(jobsRequest);
}

选择注入(inject)接口(interface):

public interface SelectionInjection
{
    public static final String GET_JOBS_TAG = "SELECTION_GET_JOBS_TAG";
    public static final String GET_TASKS_TAG = "SELECTION_GET_TASKS_TAG";
    public static final String SAVE_ENTRY_TAG ="SELECTION_SAVE_ENTRY_TAG";

    public void onGettingAllJobs(List<Job> jobs);

    public void onGettingTasksForJob(List<Task> tasks);

    public void onSavedEntry(TimeEntry savedEntry);

    public void onErrorSelection(String message);
}

选择 Activity :

public class SelectionActivity extends ActionBarActivity implements SelectionInjection {

    private static final String TAG = SelectionActivity.class.getName();

    /*
    * Init variables for Recycler Views
    * */
    private LinearLayoutManager mLayoutManager;
    private SelectJobAdapter mJobsAdapter;
    private StickyHeadersItemDecoration headers;
    private SelectTaskAdapter mSelectTaskAdapter;

    /*
    * Lists used for adapter and for storing information from server
    * */
    private List<Job> mJobs;
    private List<Task> mTasks;
    private SelectionController controller;
    private Job selectedJob;


    // Inject Views with ButterKnife
    @InjectView(R.id.select_job_recyclerview) SuperRecyclerView mJobSuperRecyclerView;
    @InjectView(R.id.select_task_recyclerview) SuperRecyclerView mTaskSuperRecyclerView;
    @InjectView(R.id.job_view)FrameLayout mJobView;
    @InjectView(R.id.task_view) FrameLayout mTaskView;
    @InjectView(R.id.toolbar_actionbar) Toolbar mToolbarAction;

    private int mAnimDuration;
//    private SelectionTask mFetchingTask; // Is it a good idea to Init it here? -> Nej
//    private SaveSelectionTask mSavingTask;


    // TODO: Figure out why after coming back again to this activity, there is only a loading wheel and nothing shows up
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_selection);
        ButterKnife.inject(this);

        /*
        *  Setting up stuff for ViewSwitching
        * */
        mTaskView.setVisibility(View.GONE); // Also set in XMl but just in case :D
        mAnimDuration = getResources()
                .getInteger(android.R.integer.config_mediumAnimTime);
        /*
        * Setting Up Action Bar
        * */
        mToolbarAction.setTitle(getString(R.string.select_job_title));
        setSupportActionBar(mToolbarAction);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setHomeButtonEnabled(true); // Hierarchical activity

        if (mJobs == null) {
            // provifing dummy test data
            Log.v(TAG, "mJobs are are null");
//            mJobs = new ArrayList<Job>();
//            List<Task> taskList = new ArrayList<Task>();
//            taskList.add(
//                    new Task(88,"Task Name Doh")
//                    );
//            taskList.add(
//                    new Task(99,"Another Task Name Doh")
//            );
//            mJobs.add(
//                    new Job(
//                            10,
//                            "Test Job",
//                            1337,
//                            "Fake Customer",
//                            taskList
//                            ));
            fetchJobs();
        }
        else
        {
            setUpJobRecyclerView();
        }
    }



    private void fetchJobs() {
        Log.v(TAG,"fetchJobs();");
//        mFetchingTask = new SelectionTask();
//        mFetchingTask.execute(); // No PAram, get all the jobs
        controller = SelectionController.getInstance(BaseActivity.currentUser,this);
        controller.getAllJobs();
    }

    private void fetchTasks(Job job){
        Log.v(TAG,"fetchTAsks()");
        try{
//            mFetchingTask = new SelectionTask();
//            mFetchingTask.execute(job);

            controller = SelectionController.getInstance(BaseActivity.currentUser,this);
            controller.getTasksForJob(job);

        }catch (Exception e){
            Log.v(TAG,"There was an error fetching tasks");
            e.printStackTrace();
            Toast.makeText(this,"There was error fetching tasks",Toast.LENGTH_LONG).show();
        }
    }


    /**
     * Method for setting up Job Recycler View
     */
    private void setUpJobRecyclerView(){
        /*
        * Setting up Jobs Recycler View
        * */
        mJobsAdapter = new SelectJobAdapter(mJobs);
        mJobsAdapter.setHasStableIds(true);
        headers = new StickyHeadersBuilder()
                .setAdapter(mJobsAdapter)
                .setRecyclerView(mJobSuperRecyclerView.getRecyclerView())
                .setStickyHeadersAdapter(new SelectJobHeaderAdapter(mJobs))
                .build();

        mJobSuperRecyclerView.setAdapter(mJobsAdapter);
        mJobSuperRecyclerView.addItemDecoration(headers);

        mLayoutManager = new LinearLayoutManager(this);
        mJobSuperRecyclerView.setLayoutManager(mLayoutManager);
        // Setting up onClickListener
        mJobSuperRecyclerView.
                addOnItemTouchListener(
                        new RecyclerUtils.RecyclerItemClickListener(
                                this,
                                new RecyclerUtils.RecyclerItemClickListener.OnItemClickListener() {
                                    @Override
                                    public void onItemClick(View view, int position) {
                                        selectedJob = mJobs.get(position);
                                        showMaterialDialog(position);
                                    }
                                }));
    }
    /**
    * Method used for settigng up and initalising all the adapters
     * for TaskRecyclerView
    * */
    private void setUpTaskRecyclerView() {
        mLayoutManager = new LinearLayoutManager(this);
        mTaskSuperRecyclerView.setLayoutManager(mLayoutManager);
        mSelectTaskAdapter = new SelectTaskAdapter(mTasks);
        mSelectTaskAdapter.setHasStableIds(true);
        headers = new StickyHeadersBuilder()
                .setAdapter(mSelectTaskAdapter)
                .setRecyclerView(mTaskSuperRecyclerView.getRecyclerView())
                .setStickyHeadersAdapter(new SelectTaskHeaderAdapter(mTasks))
                .build();

        mTaskSuperRecyclerView.setAdapter(mSelectTaskAdapter);
        mTaskSuperRecyclerView.addItemDecoration(headers);
        mTaskSuperRecyclerView.
                addOnItemTouchListener(
                        new RecyclerUtils.RecyclerItemClickListener(
                                this,
                                new RecyclerUtils.RecyclerItemClickListener.OnItemClickListener() {
                                    @Override
                                    public void onItemClick(View view, int position) {
                                        Log.v(TAG,"TaskRecyclerView onItemClick");
                                        Toast.makeText(getApplicationContext(),"The Task has been added",Toast.LENGTH_LONG).show();
//                                        mSavingTask = new SaveSelectionTask();
//                                        mSavingTask.execute(mTasks.get(position));
                                    }
                                }));

    }

    /**
     * A method that starts a corssfade Animation between JobView and TaskView
     *
     */
    private void crossfadeViews(final View fromView, View toView){
        // Set the Task view to 0% opacity but visible, so that it is visible
        // (but fully transparent) during the animation.
        toView.setAlpha(0f);
        toView.setVisibility(View.VISIBLE);

        // Animate the Task view to 100% opacity, and clear any animation
        // listener set on the view.
        toView.animate()
                .alpha(1f)
                .setDuration(mAnimDuration)
                .setListener(null);

        // Animate the Job view to 0% opacity. After the animation ends,
        // set its visibility to GONE as an optimization step (it won't
        // participate in layout passes, etc.)
        fromView.animate()
                .alpha(0f)
                .setDuration(mAnimDuration)
                .setListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        fromView.setVisibility(View.GONE);
                    }
                });
    }

    /**
     * Method that creates and shows a Dialog
     * and executes fetchTasks() if given option is picked.
     */
    private void showMaterialDialog(final int position){
        // TODO: Consider starting running he Async Task straight away as
        //       it might be likely that the user will pick "Pcik A Task" option
        //       and this might speed up the process
        Log.v(TAG,"showMAterialDialog");
        new MaterialDialog.Builder(this)
                .title("Choose Action")
                .positiveText("Add Job")
                .negativeText("Pick A Task")
                .neutralText("CANCEL")
                .callback(new MaterialDialog.ButtonCallback(){
                    @Override
                    public void onPositive(MaterialDialog dialog) {
                        // Add Job
                        Log.v(TAG,"Adding the whole Job");
//                        mSavingTask = new SaveSelectionTask();
//                        mSavingTask.execute();
                        controller = SelectionController.getInstance(BaseActivity.currentUser,SelectionActivity.this);
                        controller.saveNewTimeEntry(BaseActivity.selectedDate,selectedJob,null);
                    }

                    @Override
                    public void onNegative(MaterialDialog dialog) {
                        /**
                         *Pick a Task
                         */
                        fetchTasks(mJobs.get(position));
                        Log.v(TAG, "Switching Views");
                        crossfadeViews(mJobView, mTaskView);
                    }

                    @Override
                    public void onNeutral(MaterialDialog dialog) {
                        Log.v(TAG,"Cancelling the Dialog Choice");

                    }
                }).show();

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.global, menu);

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        try
        {
            switch(id)
            {
                case R.id.action_settings:

                    return true;
                case android.R.id.home:
                    if (mTaskView.getVisibility() == View.VISIBLE)
                    {
                        crossfadeViews(mTaskView,mJobView);
                    }
                    else
                    {
                        finish();
                    }
                    return true;
                default:
                    throw new Exception();
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public void onSavedEntry(TimeEntry savedEntry)
    {
        Log.v("SAVED ENTRY", "TRUE");
        System.out.println(savedEntry.toString());
        controller.closeQueue(SAVE_ENTRY_TAG);
    }

    @Override
    public void onGettingAllJobs(List<Job> jobs) {
        mJobs = jobs;
        setUpJobRecyclerView();
        controller.closeQueue(GET_JOBS_TAG);
    }

    @Override
    public void onGettingTasksForJob(List<Task> tasks) {
        mTasks = tasks;
        setUpTaskRecyclerView();
        controller.closeQueue(GET_TASKS_TAG);
    }

    @Override
    public void onErrorSelection(String message) {
        Log.v(TAG,"onErrorJobTask");
    }
}

Answer 1

经过大量调试，我找到了解决方案:

我制作 Controller 和注入(inject)的方式似乎并不真正适合 Android 开发，所以我将代码重新构建为 Activity 和 fragment ，现在一切正常。

编辑:

最后我弄清楚了实际问题是什么。当我将 Context 传递给 Controller 时……我只是在实际实例化它们时才这样做。而且因为 Controller 在我的例子中是单例的，所以我在重新进入 Activity 时一直在使用旧的上下文。

我不敢相信我怎么没明白。 :)