android - 如果在第二个活动中使用，RecyclerView 在屏幕上不显示任何数据，但如果在启动器活动中使用，则显示列表
问题描述
在从第一个活动（RollDiceActivity.java）单击按钮时，我将进入第二个活动，我的 recyclerview 正在获取 JSON 对象（使用 Volley）。我的代码很简单：
viewQuotesBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// created explicit intent
Intent intent = new Intent(RollDiceActivity.this,MainActivity.class);
intent.putExtra("addedRandomNo", addedRandomNo);
startActivity(intent);
finish();
}
});
第二个活动- MainActivity.java，recyclerView 在哪里，但 recyclerview 没有在屏幕上显示任何数据（但是 Log.d(TAG, response.toString() + "Size: "+response.length()); 给了我所有正在获取的 JSON 对象）
package com.subhasishlive.recyclerviewexplanation;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
import Adapter.MyAdapter;
import Model.ListItem;
import Util.Constants;
import Util.Prefs;
/**
* Created by SubhasishNath on 6/11/2018.
*/
public class MainActivity extends AppCompatActivity {
private static final String TAG = "getting length" ;
private RecyclerView recyclerView;
private MyAdapter adapter;
private List<ListItem> listItems;// listitems are movies...
private RequestQueue queue;// to use volleys
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// we are adding our queue and passing our current context....
queue = Volley.newRequestQueue(MainActivity.this);
// TODO: A FAB button would be added to call an alert dialog for search...
// now we will set up our recyclerview and setup the adapter.
recyclerView = (RecyclerView) findViewById(R.id.recyclerView1);
recyclerView.setHasFixedSize(false);
recyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
// creating an instance of Prefs class, calling parameterized constructor
// passing our mainActivity as parameter...
//Prefs prefs = new Prefs(MainActivity.this);
// calling getSearch() method
//String search = prefs.getSearch();
// ArrayLists are capable of holding any type of lists
listItems = new ArrayList<>();
// listItems is set to the returning value of getMovies(), which is a List<ListItem>
// so listItems holds all the movies returned by the search parameter.
listItems = getMovies();
adapter = new MyAdapter(MainActivity.this,listItems);// creating a new adapter for our listItems.
recyclerView.setAdapter(adapter);//setting our adapter for our recyclerView.
adapter.notifyDataSetChanged(); // Notify any registered observers that the data set has changed.
}
// creating a method to get movies...
public List<ListItem> getMovies(){
listItems.clear(); // first we're clearing the movie list....
JsonArrayRequest getRequest = new JsonArrayRequest(Request.Method.GET, Constants.base_url + "wp/v2/AllQuotes",new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
// TODO:response holds the whole JSON object from the URL
try{
Log.d(TAG, response.toString() + "Size: "+response.length());
// instantiated a new JSON array.
// Pass the name of the JSON array as parameter.
// Search is name of the JSON array from the JSON file
//JSONArray moviesArray = response.getJSONArray("Search");
// Now I'm iterating through the array by a for loop
// every index-element in that array contains a JSON object.
for(int i=0;i<response.length();i++){
// instanciating JSONObject variable to pick a Index item(which is a JSON object) from the JSONArray.
//JSONObject movieObj = moviesArray.getJSONObject(i);
ListItem movie = new ListItem();// creating ListItem object.
Log.d(TAG,"Object at " + i+ response.get(i));
// getting the JSONObject at i-th position of the JSONArray
JSONObject obj = response.getJSONObject(i);
// fetching id of each JSONObject from JSONArray.
movie.setId(obj.getInt("id"));
// title itself is an object so first I'm retrieving that
JSONObject titleObj=obj.getJSONObject("title");
// using title object I'm retrieving the string in it.
movie.setTitle(titleObj.getString("rendered"));
// content itself is an object so first I'm retriving that.
JSONObject contentObj = obj.getJSONObject("content");
// setting up the content
movie.setContent(contentObj.getString("rendered"));
// getting image object and setting up image.
JSONObject imgObj = obj.getJSONObject("better_featured_image");
movie.setPostImg(imgObj.getString("source_url"));
// getting excerpt object and setting up excerpt.
JSONObject excerptObj = obj.getJSONObject("excerpt");
movie.setPostExcerpt(excerptObj.getString("rendered"));
// adding the newly created movie to listItems list...
listItems.add(movie);
}
}catch(JSONException e){
e.printStackTrace(); // throwing an exception
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// TODO: Handle error
}
});
queue.add(getRequest);
return listItems;
}
}
但是，如果我将第二个活动（MainActivity.java）更改为我在 AndroidManifest.xml 中的启动活动，那么它会在屏幕上显示所有 recyclerView 项目以及显示日志。
<activity
android:name=".MainActivity"
android:configChanges="keyboardHidden|orientation|screenSize"
android:label="@string/app_name"
android:launchMode="singleTask">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
任何帮助将不胜感激。我很困惑，因为这个问题似乎很愚蠢。提前致谢 ：）
解决方案
您需要在列表adapter中添加数据后通知您listItems
尝试这个
在您的方法中的内部方法中adapter.notifyDataSetChanged();
添加数据后使用listItemsonResponse()getMovies()
示例代码
public List<ListItem> getMovies(){
listItems.clear(); // first we're clearing the movie list....
JsonArrayRequest getRequest = new JsonArrayRequest(Request.Method.GET, Constants.base_url + "wp/v2/AllQuotes",new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
// TODO:response holds the whole JSON object from the URL
try{
Log.d(TAG, response.toString() + "Size: "+response.length());
// instantiated a new JSON array.
// Pass the name of the JSON array as parameter.
// Search is name of the JSON array from the JSON file
//JSONArray moviesArray = response.getJSONArray("Search");
// Now I'm iterating through the array by a for loop
// every index-element in that array contains a JSON object.
for(int i=0;i<response.length();i++){
// instanciating JSONObject variable to pick a Index item(which is a JSON object) from the JSONArray.
//JSONObject movieObj = moviesArray.getJSONObject(i);
ListItem movie = new ListItem();// creating ListItem object.
Log.d(TAG,"Object at " + i+ response.get(i));
// getting the JSONObject at i-th position of the JSONArray
JSONObject obj = response.getJSONObject(i);
// fetching id of each JSONObject from JSONArray.
movie.setId(obj.getInt("id"));
// title itself is an object so first I'm retrieving that
JSONObject titleObj=obj.getJSONObject("title");
// using title object I'm retrieving the string in it.
movie.setTitle(titleObj.getString("rendered"));
// content itself is an object so first I'm retriving that.
JSONObject contentObj = obj.getJSONObject("content");
// setting up the content
movie.setContent(contentObj.getString("rendered"));
// getting image object and setting up image.
JSONObject imgObj = obj.getJSONObject("better_featured_image");
movie.setPostImg(imgObj.getString("source_url"));
// getting excerpt object and setting up excerpt.
JSONObject excerptObj = obj.getJSONObject("excerpt");
movie.setPostExcerpt(excerptObj.getString("rendered"));
// adding the newly created movie to listItems list...
listItems.add(movie);
}
adapter.notifyDataSetChanged();
}catch(JSONException e){
e.printStackTrace(); // throwing an exception
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// TODO: Handle error
}
});
queue.add(getRequest);
return listItems;
}
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