android - RecyclerView 不会立即显示任何内容

Question

我正在尝试解决与 RecyclerView 相关的问题。当我第一次尝试显示对象列表时，我什么也没看到。由于已知是异步的 volley 请求，数据得以传递。因此，我尝试了各种解决方案，例如 onDataSetChanged() 但没有任何反应。我想指出该解决方案有效，第二次查看列表时我可以毫无问题地看到它。

这是我的代码:

public class MainActivity extends AppCompatActivity {

RecyclerView recyclerView;

private static MyAdapter adapter;

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
    getSupportActionBar().setHomeButtonEnabled(false);

    recyclerView = (RecyclerView) findViewById(R.id.myRecyclerView);
    adapter = new MyAdapter(this,initData());
    adapter.setParentClickableViewAnimationDefaultDuration();
    adapter.setParentAndIconExpandOnClick(true);

    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setAdapter(adapter);
}

private List<ParentObject> initData() {
    TitleCreator titleCreator = TitleCreator.get(this);
    List<TitleParent> titles = titleCreator.getAll();
    List<ParentObject> parentObject = new ArrayList<>();

    for(TitleParent title:titles)
    {
        List<Object> childList = getList(title);
        title.setChildObjectList(childList);
        parentObject.add(title);
    }

    return parentObject;
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    ((MyAdapter)recyclerView.getAdapter()).onSaveInstanceState(outState);
}

@Override
public void onBackPressed() {
    super.onBackPressed();
    overridePendingTransition(R.anim.left_enter, R.anim.right_out);
}

private List<Object> getList(final TitleParent title){
    final List<Object> childList = new ArrayList<>();

    // Tag used to cancel the request
    String tag_string_req = "request";

    StringRequest strReq = new StringRequest(Request.Method.POST,
            AppConfig.URL_DASHBOARD, new Response.Listener<String>() {

        @Override
        public void onResponse(String response) {
            Log.d("POL", "Response: " + response.toString());

            try {
                JSONObject jObj = new JSONObject(response);

                for (int i = 0; i < jObj.getJSONArray("polizze").length(); i++) {
                    JSONObject user = jObj.getJSONArray("polizze").getJSONObject(i);
                    String certificate = user.getString("numero_contratto");
                    if(title.getTitle().contains(certificate)){
                        String scadenza = user.getString("scadenza");
                        String totale = user.getString("totale");
                        childList.add(new TitleChild(scadenza,totale));
                    }
                }
                Log.d("TRY", "Response: " + response.toString());
                adapter.notifyDataSetChanged();
            } catch (JSONException e) {
                // JSON error
                e.printStackTrace();
                //  Toast.makeText(getApplicationContext(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show();
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e("DASH", "Login Error: " + error.getMessage());
            //Toast.makeText(getApplicationContext(),
            //       error.getMessage(), Toast.LENGTH_LONG).show();
        }
    });

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(strReq, tag_string_req);

    return childList;
}

感谢您的帮助!

Answer 1

有几点

1. get list 方法在发出 volley 请求后返回空列表。
2. 确保列出来自服务器的填充数据，然后调用设置的数据。

你必须尝试像下面这样的东西。

public class MainActivity extends AppCompatActivity {

RecyclerView recyclerView;

private static MyAdapter adapter;

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
    getSupportActionBar().setHomeButtonEnabled(false);

    recyclerView = (RecyclerView) findViewById(R.id.myRecyclerView);
    // show some loading bar
     initData();

}

  private void initData() {
    TitleCreator titleCreator = TitleCreator.get(this);
    List<TitleParent> titles = titleCreator.getAll();
    List<ParentObject> parentObject = new ArrayList<>();

    for(TitleParent title:titles)
    {
        List<Object> childList = getList(title);
        title.setChildObjectList(childList);
        parentObject.add(title);
    }


}
 private void setData(List<ParentObject> parentObject) {
 // load the data here            
    adapter = new MyAdapter(this,parentObject);
            adapter.setParentClickableViewAnimationDefaultDuration();
adapter.setParentAndIconExpandOnClick(true);

recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(adapter);
}


@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    ((MyAdapter)recyclerView.getAdapter()).onSaveInstanceState(outState);
}

@Override
public void onBackPressed() {
    super.onBackPressed();
    overridePendingTransition(R.anim.left_enter, R.anim.right_out);
}

private List<Object> getList(final TitleParent title){
    final List<Object> childList = new ArrayList<>();

    // Tag used to cancel the request
    String tag_string_req = "request";

    StringRequest strReq = new StringRequest(Request.Method.POST,
            AppConfig.URL_DASHBOARD, new Response.Listener<String>() {

        @Override
        public void onResponse(String response) {
            Log.d("POL", "Response: " + response.toString());

            try {
                JSONObject jObj = new JSONObject(response);

                for (int i = 0; i < jObj.getJSONArray("polizze").length(); i++) {
                    JSONObject user = jObj.getJSONArray("polizze").getJSONObject(i);
                    String certificate = user.getString("numero_contratto");
                    if(title.getTitle().contains(certificate)){
                        String scadenza = user.getString("scadenza");
                        String totale = user.getString("totale");
                        childList.add(new TitleChild(scadenza,totale));
                    }
                 setData(childList);
                }
                Log.d("TRY", "Response: " + response.toString());

            } catch (JSONException e) {
                // JSON error
                e.printStackTrace();
                //  Toast.makeText(getApplicationContext(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show();
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e("DASH", "Login Error: " + error.getMessage());
            //Toast.makeText(getApplicationContext(),
            //       error.getMessage(), Toast.LENGTH_LONG).show();
        }
    });

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(strReq, tag_string_req);

    return childList;
}