Android Custom ListView没有与Volley一起构建

Question

我正在从公共源解析JSON数组并将它们插入到自定义ListView中。我有4节课;

1. MySingleton for Volley Requests

   public class MySingleton {
   private static MySingleton mInstance;
   private RequestQueue mRequestQueue;
   private ImageLoader mImageLoader;
   private static Context mCtx;
   
   private MySingleton(Context context) {
       mCtx = context;
       mRequestQueue = getRequestQueue();
   
       mImageLoader = new ImageLoader(mRequestQueue,
               new ImageLoader.ImageCache() {
                   private final LruCache<String, Bitmap>
                           cache = new LruCache<String, Bitmap>(20);
   
                   @Override
                   public Bitmap getBitmap(String url) {
                       return cache.get(url);
                   }
   
                   @Override
                   public void putBitmap(String url, Bitmap bitmap) {
                       cache.put(url, bitmap);
                   }
               });
   }
   
   public static synchronized MySingleton getInstance(Context context) {
       if (mInstance == null) {
           mInstance = new MySingleton(context);
       }
       return mInstance;
   }
   
   public RequestQueue getRequestQueue() {
       if (mRequestQueue == null) {
           mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
       }
       return mRequestQueue;
   }
   
   public <T> void addToRequestQueue(Request<T> req) {
       getRequestQueue().add(req);
   }
   
   public ImageLoader getImageLoader() {
       return mImageLoader;
   }}

2. GameListItem 公共类GameListItem {

   private String itemName, itemLongDescription, itemShortDescription, itemReleaseDate;
   String releaseyear;
   private int iconID, imageID;
   
   public GameListItem(String itemName, String releaseyear, int iconID) {
   
       this.itemName = itemName;
       this.releaseyear = releaseyear;
       this.iconID = iconID;
   }
   
   public String getItemName() {
   
       return itemName;
   }
   
   public String getReleaseyear() {
       return releaseyear;
   }}

3. CustomListAdapter 公共类CustomListAdapter扩展BaseAdapter {

   private Context mContext;
   private LayoutInflater mInflater;
   private List<GameListItem> mDataSource;
   
   public CustomListAdapter(Context context, List<GameListItem> items) {
       mContext = context;
       mDataSource = items;
       mInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
   }
   
   
   @Override
   public int getCount() {
       return mDataSource.size();
   }
   
   @Override
   public Object getItem(int position) {
       return mDataSource.get(position);
   }
   
   @Override
   public long getItemId(int position) {
       return position;
   }
   
   @Override
   public View getView(int position, View convertView, ViewGroup parent) {
       View rowView = mInflater.inflate(R.layout.gamelist_layout, parent, false);
   
       TextView titleTextView = (TextView) rowView.findViewById(R.id.gameTitle);
   
       TextView subtitleTextView = (TextView) rowView.findViewById(R.id.gameDescription);
   
       titleTextView.setText(mDataSource.get(position).getItemName());
       subtitleTextView.setText(mDataSource.get(position).getReleaseyear());
   
       return rowView;
   }}

4. 主要活动 公共类MainActivity扩展AppCompatActivity {

   final String TAG = this.getClass().getSimpleName();
   RequestQueue requestQueue;
   private CustomListAdapter adapter;
   private List<GameListItem> gameList;
   private GameListItem gameItem;
   ListView listView;
   
   
   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
   
       Cache cache = new DiskBasedCache(getCacheDir(), 1024*1024);
       Network network = new BasicNetwork(new HurlStack());
       requestQueue = new RequestQueue(cache, network);
       requestQueue.start();
       listView = (ListView) findViewById(R.id.gameListView);
       gameList = new ArrayList<>();
   
       //This works and gives me a ListView with 5 rows
       gameList.add(new GameListItem("Test 1", "2019", R.mipmap.ic_launcher));
       gameList.add(new GameListItem("Test 2", "2092", R.mipmap.ic_launcher));
       gameList.add(new GameListItem("Test 3", "3243", R.mipmap.ic_launcher));
       gameList.add(new GameListItem("Test 4", "2323", R.mipmap.ic_launcher));
       gameList.add(new GameListItem("Test 5", "2123", R.mipmap.ic_launcher));
   
   
       //This doesn't work...
       String url = "http://api.androidhive.info/json/movies.json";
       JsonArrayRequest stringRequest = new JsonArrayRequest(url, new Response
               .Listener<JSONArray>(){
   
           @Override
           public void onResponse(JSONArray jsonArray) {
   
               if (jsonArray == null) {
                   Toast.makeText(MainActivity.this, "jsonArray is Null", Toast.LENGTH_LONG).show();
               } else {
                   try {
                       Toast.makeText(MainActivity.this, "ATTEMPTING PARSING", Toast.LENGTH_SHORT).show();
                       Log.e("This is the json array", jsonArray.toString());
   
                       for (int i = 0; i < jsonArray.length(); i++){
   
                           JSONObject jsonObject = jsonArray.getJSONObject(i);
                           String title = jsonObject.getString("title");
                           int releaseYear = jsonObject.getInt("releaseYear");
   
                           gameList.add(new GameListItem(releaseDate, "" + releaseYear , R.mipmap.ic_launcher));
   
                           //this prints all the Titles and Release Dates correctly
                           Log.e("This is a title", title);
                           Log.e("This is a year", "HERE " + releaseYear);
   
   
   
                       }
   
                   } catch(JSONException e){
                       Log.i("JSON exception", e.toString());
                       Toast.makeText(MainActivity.this, "JSON ERROR", Toast.LENGTH_LONG).show();
                   }
   
                   requestQueue.stop();
               }
   
           }
       }, new Response.ErrorListener() {
           @Override
           public void onErrorResponse(VolleyError error) {
   
               Log.d("This is an error", ""+error.getMessage()+","+error.toString());
           }
       });
   
   
       MySingleton.getInstance(this).addToRequestQueue(stringRequest);
   
       adapter = new CustomListAdapter(this, gameList);
       listView.setAdapter(adapter);
   
   
   }}

正如在主活动中所评论的，当我手动添加一行（带有手动数据）时，ListView构建并显示，但解析器没有显示任何内容。我检查了无数的教程，一切看起来都井然有序，我甚至看了看这里，并按照大部分回答我发现什么都没有。有人可以看到导致列表不能构建/打印的错误吗？

PS。 Log.e也打印出来（在解析器里面）

谢谢！

Answer 1

如果请求成功，则必须将数据更改通知适配器。在你的情况下，adapter.notifyDataSetChanged（）;在catchRedponse里面的catch块之前。

Answer 2

在requestQueue.stop语句后添加以下行：

adapter.notifyDataSetChanged();

---

首先，当您设置适配器时，列表没有数据，因为Volley请求将异步进行，这就是为什么您需要让适配器知道其数据何时发生更改。

来自the documentation：

notifyDataSetChanged（）

通知附加的观察者基础数据已被更改，反映数据集的任何视图都应自行刷新。