Question

我正在尝试使用ProductHunt API在ListView中显示新帖子列表，并在点击时进一步展开列表项。

在打开应用程序时，会出现进度条，但之后应用程序屏幕保持空白。我认为我的OnPostExecute方法可能有一些错误，因为当我添加一个textview来显示一个字符串时，它会显示但是我的listView没有显示。

我使用标准的Apache HttpClient来处理api请求。

我有4个班级，

MainActivity.java

    package com.emoji.apisoup;

/**
 * Created by mdhalim on 16/05/16.
 */

import java.io.IOException;
import java.util.ArrayList;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;

import org.apache.http.HttpClientConnection;
import org.apache.http.HttpResponse;

import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicHttpResponse;
import org.apache.http.protocol.HTTP;






public class MainActivity extends Activity {

    private ListView lvPosts;
    private ProductHuntAdapter adapterPosts;
    public static final String POST_DETAIL_KEY = "posts";
    private ProgressDialog pDialog;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.phunt_main);
        String serverURL = "https://api.producthunt.com/v1/posts/";
        ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
        adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);


        lvPosts = (ListView) findViewById(R.id.lvPosts);



        lvPosts.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                {
                    Intent i = new Intent(MainActivity.this, ProductHuntDetail.class);
                    i.putExtra(POST_DETAIL_KEY, adapterPosts.getItem(position));
                    startActivity(i);
                }
            }
        });

        new LongOperation().execute(serverURL);


    }
        private class LongOperation extends AsyncTask<String, Void, Void> {

        private final HttpClient Content = new DefaultHttpClient();
        private String Error = null;

            @Override
            protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();

        }
            protected Void doInBackground(String... urls){

                JSONArray items = null;

                try {

                HttpGet httpget = new HttpGet(urls[0]);
                httpget.setHeader("Accept","application/json");
                httpget.setHeader("Content-Type","application/json");
                httpget.setHeader("Authorization","Bearer 2587aa878d7334e3c89794a6b73ebffb59a06c23b82cd0f789d2ab72d2417739");
                ResponseHandler<String> responseHandler = new BasicResponseHandler();

                String jsonStr = Content.execute(httpget, responseHandler);
                    Log.d("Response: ", "> " + jsonStr);

                JSONObject jsonObj = new JSONObject(jsonStr);

                    items = jsonObj.getJSONArray("posts");

                    // Parse json array into array of model objects
                    ArrayList<ProductHuntList> posts = ProductHuntList.fromJson(items);

                    // Load model objects into the adapter
                    for (ProductHuntList post : posts) {
                        adapterPosts.add(post);
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    Error = e.getMessage();
                    cancel(true);
                }
                return null;
            }

            @Override
            protected void onPostExecute(Void result) {

                super.onPostExecute(result);
                // Dismiss the progress dialog
                if (pDialog.isShowing())
                    pDialog.dismiss();

                ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
                adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
                lvPosts.setAdapter(adapterPosts);
            }
        }

}

ProductHuntList.java 包含JSON数据模型和反序列化器以及用于解析JSON数组的静态方法

  package com.emoji.apisoup;


import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.io.Serializable;


/**
 * Created by mdhalim on 18/05/16.
 */

public class ProductHuntList implements Serializable {
    private static final long serialVersionUID = -8959832007991513854L;

    private String name;
    private String tagline;
    private String screenshot_url;
    private String largePosterUrl;
    private String discussion_Url;
    private String created_at;
    private int votes_count;


    public String getNames() {

        return name;
    }

    public String getCreated_at() {
        return created_at;
    }

    public String getScreenshot_url() {
        return screenshot_url;
    }

    public String getDiscussion_Url() {
        return discussion_Url;
    }

    public int getVotes_count() {
        return votes_count;
    }

    public String getLargePosterUrl() {
            return largePosterUrl;
        }
    public String getTagline(){
        return tagline;
    }


    public static ProductHuntList fromJson(JSONObject jsonObject) {
        ProductHuntList b = new ProductHuntList();
        try {
            // Deserialize json into object fields
            b.name = jsonObject.getString("name");
            b.created_at = jsonObject.getString("created_at");
            b.tagline = jsonObject.getString("tagline");
            b.screenshot_url = jsonObject.getJSONObject("screenshot_url").getString("300px");
            b.largePosterUrl = jsonObject.getJSONObject("screenshot_url").getString("850px");
            b.votes_count = jsonObject.getInt("votes_count");
            b.discussion_Url = jsonObject.getString("discussion_url");


        } catch (JSONException e) {
            e.printStackTrace();
            return null;
        }
        // Return new object
        return b;

    }

    public static ArrayList<ProductHuntList> fromJson(JSONArray jsonArray) {
        ArrayList<ProductHuntList> posts = new ArrayList<ProductHuntList>(jsonArray.length());

        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject productJson = null;
            try {
                productJson = jsonArray.getJSONObject(i);
            } catch (Exception e) {
                e.printStackTrace();
                continue;
            }

            ProductHuntList post = ProductHuntList.fromJson(productJson);
            if (post != null)
            {
                posts.add(post);
            }
        }

        return posts;
    }

}

ProductHuntAdapter.java 这实现了ArrayAdapter

package com.emoji.apisoup;

/**
 * Created by mdhalim on 18/05/16.
 */

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.squareup.picasso.Picasso;

import java.util.ArrayList;

/**
 * Created by mdhalim on 18/05/16.
 */
public class ProductHuntAdapter extends ArrayAdapter<ProductHuntList> {
    public ProductHuntAdapter(Context context, ArrayList<ProductHuntList> aPosts) {
        super(context, 0, aPosts);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Get the data item for this position
        ProductHuntList posts = getItem(position);
        // Check if an existing view is being reused, otherwise inflate the view
        if (convertView == null) {
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(R.layout.item_product_hunt, null);
        }
        // Lookup view for data population
        TextView name = (TextView) convertView.findViewById(R.id.name);
        TextView created = (TextView) convertView.findViewById(R.id.created);
        TextView tagline = (TextView) convertView.findViewById(R.id.tagline);
        ImageView ivPosterImage = (ImageView) convertView.findViewById(R.id.ivPosterImage);

        // Populate the data into the template view using the data object
        name.setText(posts.getNames());
        created.setText("Created On: " + posts.getCreated_at() + "%");
        tagline.setText(posts.getTagline());
        Picasso.with(getContext()).load(posts.getScreenshot_url()).into(ivPosterImage);
        // Return the completed view to render on screen
        return convertView;
    }
}

最后，当用户点击列表中的任何项目时，实现项目详细信息活动的类。 ProductHuntDetail

package com.emoji.apisoup;

/**
 * Created by mdhalim on 18/05/16.
 */
        import android.annotation.SuppressLint;
        import android.app.Activity;
        import android.os.Bundle;
        import android.text.Html;
        import android.widget.ImageView;
        import android.widget.TextView;

        import com.squareup.picasso.Picasso;

public class ProductHuntDetail extends Activity {
    private ImageView ivPosterImage;
    private TextView name;
    private TextView discusUrl;
    private TextView upvotes;
    private TextView tagline;
    private TextView created;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.product_hunt_detail);
        // Fetch views
        ivPosterImage = (ImageView) findViewById(R.id.ivPosterImage);
        name = (TextView) findViewById(R.id.name);
        discusUrl = (TextView) findViewById(R.id.discusUrl);
        created = (TextView) findViewById(R.id.created);
        upvotes =  (TextView) findViewById(R.id.upvotes);
        tagline = (TextView) findViewById(R.id.tagline);
        // Load movie data
        ProductHuntList posts = (ProductHuntList) getIntent().getSerializableExtra(MainActivity.POST_DETAIL_KEY);
        loadMovie(posts);
    }

    // Populate the data for the movie
    @SuppressLint("NewApi")
    public void loadMovie(ProductHuntList posts) {
        // Populate data
        name.setText(posts.getNames());
        upvotes.setText(Html.fromHtml("<b>Upvotes:</b> " + posts.getVotes_count() + "%"));
        created.setText(posts.getCreated_at());
        tagline.setText(posts.getTagline());
        discusUrl.setText(Html.fromHtml("<b>Discussion Url:</b> " + posts.getDiscussion_Url()));
        // R.drawable.large_movie_poster from
        // http://content8.flixster.com/movie/11/15/86/11158674_pro.jpg -->
        Picasso.with(this).load(posts.getLargePosterUrl()).
                placeholder(R.drawable.large_movie_poster).
                into(ivPosterImage);
    }

}

我一直试图调试这几个小时：/

Answer 1

您的异步任务正在返回空白。

protected void onPostExecute(Void result) {

            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();

            ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
            adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
            lvPosts.setAdapter(adapterPosts);
        }

据我所知，代码中的aPosts是空的。

我认为你的异步任务应该是 -

 AsyncTask<String, Void, ProductHuntAdapter>

并删除 -

 adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);

您正在使用doInBackground()方法创建并更新此内容。

Answer 2

我明白了！

我不需要在onPostExecute（）方法中再次声明这些行

ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);

所以基本上，我的新onPostExecute（）方法就像这样

protected void onPostExecute(Void result) {

            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            lvPosts.setAdapter(adapterPosts);
        }

我过去2个小时一直试图找到这个错误，因此更难，我甚至没有收到任何错误。一旦我在StackOverFlow上发布它，似乎我有神圣的干预。

在log.d中获取json响应但不在app内部（包含代码）

2 个答案: