Question

我想通过使用Asynctask从json获取图像url并在RecyclerView的帮助下将其设置在ImageView上。但是当我执行代码时它没有显示任何内容，这里是我的Json文件

[
  {
    "albumId": 1,
    "id": 1,
    "title": "accusamus beatae ad facilis cum similique qui sunt",
    "url": "http://placehold.it/600/92c952",
    "thumbnailUrl": "http://placehold.it/150/92c952"
  },
  {
    "albumId": 1,
    "id": 2,
    "title": "reprehenderit est deserunt velit ipsam",
    "url": "http://placehold.it/600/771796",
    "thumbnailUrl": "http://placehold.it/150/771796"
  }

]

这是我的主要活动

public class MainActivity extends AppCompatActivity {
ProgressDialog progressDialog;
private RecyclerView.LayoutManager mLayoutManager;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler);
    mLayoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.addItemDecoration(new SimpleDivider(MainActivity.this));
    RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(this);
    recyclerView.setAdapter(recyclerViewAdapter);
    new MyAsyncTask().execute();
}


private class MyAsyncTask extends AsyncTask<Object, Object, String> {


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }

    @Override
    protected String doInBackground(Object... params) {
        StringBuffer chaine = new StringBuffer("");

        try {
            URL url = new URL("https://jsonplaceholder.typicode.com/photos");
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setDoInput(true);
            urlConnection.connect();
            InputStream inputStream = urlConnection.getInputStream();
            BufferedReader rd = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while ((line = rd.readLine()) != null) {
                chaine.append(line);
            }


        } catch (IOException e) {
            e.printStackTrace();
        }
        String result = chaine.toString();
        return result;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        JB jb = new JB();
        try {
            JSONArray jArray = new JSONArray(result);
            for (int i = 0; i < jArray.length(); i++) {

                JSONObject jObject = jArray.getJSONObject(i);
                String image = jObject.getString("url");
                jb.setAndroid_image_url(image);
            }

        } catch (JSONException e) {
            Log.e("JSONException", "Error: " + e.toString());
        }
    }
}

}

这是我的RecyclerAdapter

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {
ArrayList<JB> jbs;
private Context context;


public RecyclerViewAdapter(Context context) {
    this.context = context;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(context).inflate(R.layout.image_layout, parent, false);
    return new ViewHolder(itemView);

}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    Picasso.with(context).load(jbs.get(position).getAndroid_image_url()).resize(120, 60).into(holder.imageView);
}

@Override
public int getItemCount() {
    return 0;
}

public class ViewHolder extends RecyclerView.ViewHolder {
    ImageView imageView;

    public ViewHolder(View itemView) {
        super(itemView);
        imageView = (ImageView) itemView.findViewById(R.id.image);

    }
}

}

我正在使用picaso将照片加载到ImageView

Answer 1

我认为你错过了什么，我做了一些改变。更新你的代码

更新onPostExecute

<div id="someImg" width="332px" height="300px">

</div>

更新RecyclerView适配器构造函数

@Override
protected void onPostExecute(String result) {
    super.onPostExecute(result);
    ArrayList<JB> jb = new ArrayList<JB>();
    try {
        JSONArray jArray = new JSONArray(result);
        for (int i = 0; i < jArray.length(); i++) {

            JSONObject jObject = jArray.getJSONObject(i);
            String image = jObject.getString("url");
            jb.setAndroid_image_url(image);
        }

  // remove below code from your OnCreate

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler);
        mLayoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(mLayoutManager);
        recyclerView.addItemDecoration(new SimpleDivider(MainActivity.this));
        RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(this, jb);
        recyclerView.setAdapter(recyclerViewAdapter);

    } catch (JSONException e) {
        Log.e("JSONException", "Error: " + e.toString());
    }
}

Answer 2

您必须创建JB类的ArrayList，然后传递给recyclerview适配器。

public static void createPipeline(Class<?> fnClass){
  Pipeline p = TestPipeline.create();
  p.apply(new Source()).apply(fnClass.newInstance());
  p.apply(new AnotherSource()).apply(fnClass.newInstance());
  p.run;
}

在RecyclerViewAdapter中，更改构造函数。

    ArrayList<JB> jbArray = new ArrayList();
    JB jb;
    try {
        JSONArray jArray = new JSONArray(result);
        for (int i = 0; i < jArray.length(); i++) {
            jb = new JB();
            JSONObject jObject = jArray.getJSONObject(i);
            String image = jObject.getString("url");
            jb.setAndroid_image_url(image);
            jbArray.add(jb);
        }
    recyclerViewAdapter = new RecyclerViewAdapter(this ,jbArray);
    recyclerView.setAdapter(recyclerViewAdapter);
    } catch (JSONException e) {
        Log.e("JSONException", "Error: " + e.toString());
    }

Answer 3

初始化数组

ArrayList<JB> yourarray = new ArrayList;

@Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            JB jb = new JB();
            try {
                JSONArray jArray = new JSONArray(result);
                for (int i = 0; i < jArray.length(); i++) {
                    jb = new JB();
                    JSONObject jObject = jArray.getJSONObject(i);
                    String image = jObject.getString("url");
                    jb.setAndroid_image_url(image);
                    yourarray.add(jb);


                }

        RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(this,yourarray);
        recyclerView.setAdapter(recyclerViewAdapter,yourarray);

            } catch (JSONException e) {
                Log.e("JSONException", "Error: " + e.toString());
            }
    }

更新适配器构造函数

public RecyclerViewAdapter(Context context,ArrayList<JB> jbs) {
    this.context = context;
    this.jbs=jbs;
}

Answer 4

首先，你需要使用JB的ArrayList，因为在onPostExecute中你创建了一个JB对象并在每次循环迭代中覆盖数据。

其次，您不要在适配器中设置数据集。适配器始终在getItemCount方法中返回0。尝试类似：

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {
    private ArrayList<JB> jbs;
    private Context context;

    public setData(ArrayList<JB> list) {
        jbs = list;
        notifyDataSetChanged();
    }

    <...>

    @Override
    public int getItemCount() {
        return jbs != null ? jbs.size() : 0;
    }
}

在onPostExecute：

@Override
protected void onPostExecute(String result) {
    super.onPostExecute(result);
    ArrayList<JB> jbList = new ArrayList<>();
    try {
        JSONArray jArray = new JSONArray(result);
        for (int i = 0; i < jArray.length(); i++) {
            JB curJb = new JB();
            JSONObject jObject = jArray.getJSONObject(i);
            String image = jObject.getString("url");
            curJb.setAndroid_image_url(image);
            jbList.add(curJb);
        }
    recyclerViewAdapter.setData(jbList); //don't forget make recycleViewAdapter available in this scope
    } catch (JSONException e) {
        Log.e("JSONException", "Error: " + e.toString());
    }
}

不使用asynctask从json中恢复图像

4 个答案: