GridView在适配器获取新项后没有更新其子视图

Question

我一直在寻找原因，想知道我的代码为什么会出问题。我有一个GridView，它有一个ArrayAdapter，使用AsyncTask拉取图片。我可以看到项被更新，但是当我尝试更新适配器时，GridView似乎没有使用新视图进行更新。

这是相关的工作代码...

private void fetchJsonResponse(String url) {
    // Pass second argument as "null" for GET requests
    JsonObjectRequest req = new JsonObjectRequest(Request.Method.GET,
            url + "&api_key=" + API_KEY,
            null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray photos = response.getJSONArray("photos");

                        for(int i = 0; i < photos.length(); i++){
                            JSONObject object = photos.getJSONObject(i);
                            String url = object.getString("img_src");
                            //String id = object.getString("id");
                            list.add(new ImageItem(null, "Picture", url));
                            Log.i("Debug 2", url);
                        }
                        Log.i("Debug 2", list.get(0).toString());

                        if(gridViewAdapter != null){
                            gridViewAdapter.clear();
                            gridViewAdapter.addAll(list);
                            gridViewAdapter.notifyDataSetChanged();
                            gridView.invalidateViews();
                        } else {
                            gridViewAdapter = new GridViewAdapter(getActivity(), R.layout.gridview_item, list);
                            gridView.setAdapter(gridViewAdapter);
                        }




                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.e("Error: ", error.getMessage());
        }
    });



    /* Add your Requests to the RequestQueue to execute */
    mRequestQueue.add(req);

}

private class MyAsyncTask extends AsyncTask<String, Void, Void> {
    private ProgressDialog progressDialog;
    private Context context;

    public MyAsyncTask (Context context){
        this.context = context;
        progressDialog = new ProgressDialog(getActivity());
        progressDialog.setMessage("Contacting Rover...");
    }

    @Override
    protected Void doInBackground(String... strings) {
        fetchJsonResponse(strings[0]);
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        Toast.makeText(getActivity(), "In Pre Execute", Toast.LENGTH_SHORT).show();
        progressDialog.show();

    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        progressDialog.dismiss();
    }
}

如果可能的话，我真的很感激您的任何帮助。试图在新年前推出应用程序 :).

也许如果您能告诉我为什么会发生这种情况，那么它就不会再次引起问题，并且其他人也会看到。

编辑：添加了更多代码，点击按钮两次后它会刷新。

private void fetchJsonResponse(String url) {
    // Pass second argument as "null" for GET requests
    JsonObjectRequest req = new JsonObjectRequest(Request.Method.GET,
            url + "&api_key=" + API_KEY,
            null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray photos = response.getJSONArray("photos");
                        list.clear();
                        for(int i = 0; i < photos.length(); i++){
                            JSONObject object = photos.getJSONObject(i);
                            String url = object.getString("img_src");
                            list.add(new ImageItem(null, "Picture", url));
                            Log.i("Debug 2", url);
                        }
                        Log.i("Debug 2", list.get(0).toString());

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.e("Error: ", error.getMessage());
        }
    });



    /* Add your Requests to the RequestQueue to execute */
    mRequestQueue.add(req);

}

private class MyAsyncTask extends AsyncTask<String, Void, Void> {
    private ProgressDialog progressDialog;
    private Context context;

    public MyAsyncTask (Context context){
        this.context = context;

        progressDialog = new ProgressDialog(getActivity());
        progressDialog.setMessage("Contacting Rover...");
        pictureAdapter = new PictureAdapter(getActivity(), list);
        gridView.setAdapter(pictureAdapter);
    }

    @Override
    protected Void doInBackground(String... strings) {
        fetchJsonResponse(strings[0]);
        return null;
    }

    @Override
    protected void onPreExecute() {
        progressDialog.show();
        super.onPreExecute();
        Toast.makeText(getActivity(), "In Pre Execute", Toast.LENGTH_SHORT).show();


    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);

        pictureAdapter.updateItemList(list);
        gridView.invalidate();

        progressDialog.dismiss();
    }
}

Adapter:

public class PictureAdapter extends BaseAdapter {
private ArrayList<ImageItem> items;
private Context context;
private TextView titleText;
private ImageView itemImage;

public PictureAdapter(Context context, ArrayList<ImageItem> items){
    this.context = context;
    this.items = items;
}

@Override
public int getCount() {
    return items.size();
}

@Override
public Object getItem(int position) {
    return items.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View v = LayoutInflater.from(context).inflate(R.layout.gridview_item, parent, false);

    titleText = (TextView) v.findViewById(R.id.text);
    itemImage = (ImageView)v.findViewById(R.id.image);

    titleText.setText(items.get(position).getTitle());
    Picasso.with(context).load(items.get(position).getUrl()).fit().into(itemImage);

    return v;
}

public void updateItemList(ArrayList<ImageItem> newItemList){
    this.items = newItemList;
    notifyDataSetChanged();
}

}

- SmiffyKmc

---

如果您正在进行活动，则在runOnUiThread()方法内更新您的GridView，或者使用Handler在UI线程上运行。 - sohan shetty

我将应该更新GridView的if/else部分放入了onPostExecute中，因为它在UI线程上运行，但现在似乎根本没有更新... - SmiffyKmc

请查看这个问题 - 你可以将列表作为doInBackground的返回值传递，使用获取到的数据在onPostExecute中更新你的UI。像这样做：list.clear(); list.addAll(listFromDoInBackground); adapter.notifyDataSetChanged(); 或者如果为空，则实例化一个新的adapter。我还建议使用ViewHolder模式或RecyclerView。 - yennsarah

如果您正在使用Volley，则不需要使用asynctask，可以将其删除。 - Narendra Kothamire

你试过用断点和流程吗？ - Noorul

Answer 1

在 post execute 中尝试以下代码：

@Override
protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);

    pictureAdapter.updateItemList(list,gridView);
    progressDialog.dismiss();
}

现在在您的updateItemList中。

public void updateItemList(ArrayList<ImageItem> newItemList,GridView gridView){
    this.items = newItemList;

    gridView.setAdapter(null);
    gridView.invalidateViews();
    gridView.deferNotifyDataSetChanged();

    gridView.setAdapter(list);

}

- Ranjan

Answer 2

为什么你要在AsyncTask中调用Volley请求，因为Volley会在NetworkThread上执行请求。

移除AsyncTask并直接调用Volley。

试一下这个方法，希望能帮到你。

private ProgressDialog progressDialog;

protected void onCreate(Bundle savedInstanceState) {
    progressDialog = new ProgressDialog(getActivity());
    progressDialog.setMessage("Contacting Rover...");
    progressDialog.show();
    fetchJsonResponse(url); 
}

private void fetchJsonResponse(String url) {
    // Pass second argument as "null" for GET requests
    JsonObjectRequest req = new JsonObjectRequest(Request.Method.GET,
            url + "&api_key=" + API_KEY,
            null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    progressDialog.dismiss();
                    try {
                        JSONArray photos = response.getJSONArray("photos");
                        list.clear();
                        for(int i = 0; i < photos.length(); i++){
                            JSONObject object = photos.getJSONObject(i);
                            String url = object.getString("img_src");
                            list.add(new ImageItem(null, "Picture", url));
                            Log.i("Debug 2", url);
                        }
                        pictureAdapter.notifyDataSetChanged();
                        Log.i("Debug 2", list.get(0).toString());

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, 
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    progressDialog.dismiss();
                    VolleyLog.e("Error: ", error.getMessage());
                }
            });
    /* Add your Requests to the RequestQueue to execute */
    mRequestQueue.add(req);
}

- Jaymin Panchal