如何從URL請求和獲取jsonarray並在Android中的ListView上查看它們

Question

我是Android Studio的新手，我想創建一個RSS閱讀器應用程序。 應用程序應從url獲取最新新聞ID，將其與應用程序中現有的最新新聞ID進行比較，發送請求並獲取它們之間的每個ID的json數組。下載json完成后，將其顯示在列表視圖中。 問題是我不知道如何將它們添加到列表視圖。 MainActivity類是：

//sorry guys this class is totally messed up!
package com.example.sorush.slidr;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

import com.example.sorush.slidr.model.NewsItems;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import com.r0adkll.deadskunk.adapters.BetterRecyclerAdapter;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Type;
import java.util.List;

import butterknife.ButterKnife;
import butterknife.InjectView;


public class MainActivity extends ActionBarActivity {

@InjectView(R.id.recycler)
RecyclerView mRecycler;

private OSVersionAdapter mAdapter;
List<NewsItems> oss = null;

int i=1;
String lastidurl = api + "name=getnewsid";
String URL = api + "name=getnews" + i;
private final static  String api = "api link";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.inject(this);
    new DownloadFilesTask();

}

/**
 * Intialize Recycler
 */
private void initRecycler(){
    mAdapter = new OSVersionAdapter();
    mAdapter.addAll(getJSONFromUrl(URL));
    mRecycler.setAdapter(mAdapter);
    mRecycler.setLayoutManager(new LinearLayoutManager(this));
    mAdapter.setOnItemClickListener(new BetterRecyclerAdapter.OnItemClickListener<NewsItems>() {
        @Override
        public void onItemClick(View view, NewsItems androidOS, int i) {
            // Launch the slidable activity
            Intent viewer = new Intent(MainActivity.this, ViewerActivity.class);
            viewer.putExtra(ViewerActivity.EXTRA_OS, androidOS);
            startActivity(viewer);
        }
    });
}

private class DownloadFilesTask extends AsyncTask<String, Integer, Void> {

    @Override
    protected void onProgressUpdate(Integer... values) {
    }

    @Override
    protected void onPostExecute(Void result) {
        if (oss != null) {
            initRecycler();
        }
    }

    @Override
    protected Void doInBackground(String... params) {
        String lastid;
        lastid = getLastNewsID(lastidurl);
        int id = Integer.parseInt(lastid);

        if(lastid!=null) {
            for (i = 0; i < id ; i++) {
                 String url = params[i];
                getJSONFromUrl(url);

            }
        }else{
            //
        }
        if(i==lastid.length()){
            Intent intent = new Intent(MainActivity.this,     ViewerActivity.class);
            PendingIntent contentIntent =     PendingIntent.getActivity(MainActivity.this, 0, intent,     PendingIntent.FLAG_UPDATE_CURRENT);

            NotificationCompat.Builder b = new NotificationCompat.Builder(MainActivity.this);

            b.setAutoCancel(true)
                    .setDefaults(Notification.DEFAULT_ALL)
                    .setWhen(System.currentTimeMillis())
                    .setSmallIcon(R.drawable.ic_launcher)
                    .setTicker("News")
                    .setContentTitle("News Available")
                    .setContentText("news text")
                    .setDefaults(Notification.DEFAULT_LIGHTS| Notification.DEFAULT_SOUND)
                    .setContentIntent(contentIntent)
                    .setContentInfo("Info");


            NotificationManager notificationManager = (NotificationManager) MainActivity.this.getSystemService(Context.NOTIFICATION_SERVICE);
            notificationManager.notify(1, b.build());
        }
        return null;
    }
}
public List<NewsItems> getJSONFromUrl(String url) {
    InputStream is = null;

    // Making HTTP request
    try {

        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();

        InputStreamReader isr = new InputStreamReader(is);
        Gson gson = new Gson();
        Type listType = new TypeToken<List<NewsItems>>(){}.getType();
        oss = gson.fromJson(isr, listType);

        is.close();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return oss;

}
public final static String getLastNewsID(String s){

    InputStream is = null;
    JSONObject jObj = null;
    String id = null;
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(s);

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();

        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "UTF-8"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        id = sb.toString();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return id;
  }

}

和NewsItems類：

package com.example.sorush.slidr.model;

import android.os.Parcel;
import android.os.Parcelable;

public class NewsItems implements Parcelable{
public String author;
public String newstitle;
public int newsid;
public String thumb;
public String date;
public String content;

public NewsItems(){}

private NewsItems(Parcel in){
    author = in.readString();
    newstitle = in.readString();
    newsid = in.readInt();
    thumb = in.readString();
    date = in.readString();
    content = in.readString();
}

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

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(author);
    dest.writeString(newstitle);
    dest.writeInt(newsid);
    dest.writeString(thumb);
    dest.writeString(date);
    dest.writeString(content);
}

public static final Creator<NewsItems> CREATOR = new Creator<NewsItems>() {
    @Override
    public NewsItems createFromParcel(Parcel source) {
        return new NewsItems(source);
    }

    @Override
    public NewsItems[] newArray(int size) {
        return new NewsItems[size];
        }
    };

}

Answer 1

由於您將NewsItems保留在列表中，因此我建議使用ArrayAdapter將數據與ListView綁定。 這是我使用的適配器的示例。

public class ResultAdapter extends ArrayAdapter<Result> {
private List<Result> items;
private Context context;

static class ViewHolder {
    public ImageView icon;
    public TextView title;
    public TextView type;
}

public ResultAdapter(Context context, int resource, List<Result> objects) {
    super(context, resource, objects);
    this.context = context;
    items = objects;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // ViewHolder pattern - view stores its subviews when it's created. Next time the view is looked up it
    // reuses the views (no need to search for those again)
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.result_item, parent, false);

        ViewHolder viewHolder = new ViewHolder();
        viewHolder.icon = (ImageView) convertView.findViewById(R.id.result_item_icon);
        viewHolder.title = (TextView) convertView.findViewById(R.id.result_item_title);
        viewHolder.type = (TextView) convertView.findViewById(R.id.result_item_type);
        convertView.setTag(viewHolder);
    }
    // now the ViewHolder is prepared, next get its tag and prepare the view
    ViewHolder holder = (ViewHolder) convertView.getTag();
    Result result = items.get(position);
    holder.title.setText(result.text);
    // the Utils class is my own helper function that get me what I need from config
    holder.type.setText(Utils.getTypeString(context, result.type, true));
    holder.icon.setImageResource(Utils.getTypeSearchDrawable(result.type));
    holder.title.setTextColor(Utils.getTypeColor(context, result.type));

    return convertView;
} }

然后在您的活動中，將ListView的適配器設置為所需的適配器：

ArrayList<Result> results = new ArrayList<Result>();
// fill the ArrayList results with data - you would probably get it already filled from your AsyncTask
results.add(...);
ListView list = (ListView) findViewById(R.id.result_list_view);
list.setAdapter(new ResultAdapter(this, R.id.list_item, results));

一些注意事項：

• ViewHolder模式不是必需的，但是當我不使用它時，Eclipse會警告我。 它加快了ListView的滾動。
• 您正在使用AsyncTask加載數據。 IMO，最好在活動中為AsyncTaskLoader對其進行更改，這將為您管理配置更改（屏幕旋轉等）。 關於AsyncTaskLoader的很好的解釋： http : //www.javacodegeeks.com/2013/01/android-loaders-versus-asynctask.html