デバイスがオフラインのときに使用するJSONレスポンスのキャッシュ

Question

ニュースアプリを構築していて、ネットワークがないときに使用するJSONレスポンスをキャッシュしたいとします。私はたくさんの方法を試しましたが、それは私にとってはうまくいかなかったのです。

私の非同期タスクと私のアダプタは、リストが新しいアイテムを読み込むときに別の問題です。それは画面の上部に移動し、その後にアイテムを追加します。これをどうすれば解決できますか？

private class jsontask extends AsyncTask<String, String, List<newsmodel>> { 
    @Override 
    protected List<newsmodel> doInBackground(String... params) { 
     BufferedReader reader = null; 
     HttpURLConnection connection = null; 
     try { 
      URL url = new URL(params[0]); 

      connection = (HttpURLConnection) url.openConnection(); 

      connection.connect(); 
      InputStream stream = connection.getInputStream(); 
      reader = new BufferedReader(new InputStreamReader(stream)); 
      StringBuffer buffer = new StringBuffer(); 
      String line = ""; 
      while ((line = reader.readLine()) != null) { 
       buffer.append(line); 
      } 

      String finaljson = buffer.toString(); 
      JSONObject parentobject = new JSONObject(finaljson); 

      JSONArray parentarray = parentobject.getJSONArray("articles"); 

      for (int i = 0; i < parentarray.length(); i++) { 
       JSONObject finalobject = parentarray.getJSONObject(i); 
       newsmodel newsmodel = new newsmodel(); 
       newsmodel.setAuthor(finalobject.getString("author")); 
       if (finalobject.isNull("author")) { 
       } 
       newsmodel.setDescription(finalobject.getString("description")); 
       newsmodel.setTitle(finalobject.getString("title")); 
       newsmodel.setImage(finalobject.getString("urlToImage")); 
       newsmodel.setUrl(finalobject.getString("url")); 
       newsmodel.setPublishedAt(finalobject.getString("publishedAt")); 

       moviemodelList.add(newsmodel); 
      } 

      return moviemodelList; 

     } catch (MalformedURLException e) { 
      e.printStackTrace(); 
return moviemodelList; 
     } catch (IOException e) { 
      e.printStackTrace(); 
      return moviemodelList; 
     } catch (JSONException e) { 

     } finally { 
      if (connection != null) { 
       connection.disconnect(); 
      } 
      try { 
       if (reader != null) { 
        reader.close(); 
       } 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } 
     } 

     return null; 
    } 

    @Override 
    protected void onPostExecute(List<newsmodel> result) { 

     super.onPostExecute(result); 
     newsadapter adapter = new newsadapter(getApplicationContext(), R.layout.row, result); 
     lvnews.setAdapter(adapter); 
    } 
} 

public class newsadapter extends ArrayAdapter { 
    private List<newsmodel> moviemodelList; 
    private int resource; 
    private LayoutInflater inflater; 

    public newsadapter(Context context, int resource, List<newsmodel> objects) { 
     super(context, resource, objects); 
     moviemodelList = objects; 
     this.resource = resource; 
     inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE); 
    } 

    @Override 
    public View getView(final int position, View convertView, ViewGroup parent) { 
     viewholder holder = null; 
     if (convertView == null) { 
      holder = new viewholder(); 
      convertView = inflater.inflate(resource, null); 
      holder.newsimage = (ImageView) convertView.findViewById(R.id.imageView2); 
      holder.title = (TextView) convertView.findViewById(R.id.textView2); 
      holder.description = (TextView) convertView.findViewById(R.id.textView3); 
      holder.author = (TextView) convertView.findViewById(R.id.textView4); 
      holder.publishdate = (TextView) convertView.findViewById(R.id.textView5); 
      holder.dotsmenu = (ImageButton) convertView.findViewById(R.id.dots); 
      convertView.setTag(holder); 
     } else { 
      holder = (viewholder) convertView.getTag(); 
     } 

     final ProgressBar progressBar; 
     progressBar = (ProgressBar) convertView.findViewById(R.id.progressBar); 
     ImageLoader.getInstance().displayImage(moviemodelList.get(position).getImage(), holder.newsimage, new ImageLoadingListener() { 
      @Override 
      public void onLoadingStarted(String imageUri, View view) { 
       progressBar.setVisibility(view.VISIBLE); 
      } 

      @Override 
      public void onLoadingFailed(String imageUri, View view, FailReason failReason) { 
       progressBar.setVisibility(view.GONE); 
      } 

      @Override 
      public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) { 
       progressBar.setVisibility(view.GONE); 
      } 

      @Override 
      public void onLoadingCancelled(String imageUri, View view) { 
       progressBar.setVisibility(view.GONE); 
      } 
     }); 
     holder.title.setText(moviemodelList.get(position).getTitle()); 
     holder.description.setText(moviemodelList.get(position).getDescription()); 
     holder.author.setText(moviemodelList.get(position).getAuthor()); 
     holder.publishdate.setText(moviemodelList.get(position).getPublishedAt()); 
     final viewholder finalHolder = holder; 
     holder.dotsmenu.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       PopupMenu popup = new PopupMenu(page.this, finalHolder.dotsmenu); 
       //Inflating the Popup using xml file 
       popup.getMenuInflater().inflate(R.menu.dots_menu, popup.getMenu()); 
       popup.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() { 
        @Override 
        public boolean onMenuItemClick(MenuItem item) { 
         switch (item.getItemId()) { 

          case R.id.share: 
           Intent sendIntent = new Intent(); 
           sendIntent.setAction(Intent.ACTION_SEND); 
           sendIntent.putExtra(Intent.EXTRA_TEXT, moviemodelList.get(position).getUrl()); 
           sendIntent.setType("text/plain"); 
           startActivity(sendIntent); 
           return true; 
         } 
         return false; 
        } 

       }); 
       popup.show(); 
      } 
     }); 
     lvnews.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

       Intent intent = new Intent(page.this, webview.class); 
       intent.putExtra("Link", moviemodelList.get(position).getUrl()); 
       startActivity(intent); 
      } 
     }); 

     return convertView; 
    } 

Answer 1

ネット接続が可能かどうかをテストするためのクラスを作成します。

ConnectionDetector.java

public class ConnectionDetector { 
public Context context; 
public ConnectionDetector(Context context) 
{ 
    this.context=context; 
} 
public boolean isConnecting() { 
    ConnectivityManager check=(ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE); 
    if (check!=null){ 
     NetworkInfo[] infos=check.getAllNetworkInfo(); 
     for (int i=0;i<infos.length;i++) 
     { 
      if (infos[i].getState()== NetworkInfo.State.CONNECTED) 
       return true; 
     }} 

    return false; 

} 
} 

上記クラスのオブジェクトOBを作成します。

ConnectionDetector ob=new ConnectionDetector(getApplicationContext()); 

グローバル変数としてこれらの変数を宣言します。

File httpCacheDir; 
    long httpCacheSize = 5 * 1024 * 1024;// In place of 5 you can use size in mb 
    HttpResponseCache cache; 

は（）関数のキャッシャを行います。

public void cacher() 
{ 
    httpCacheDir = getExternalCacheDir(); 

    // Cache Size of 5MB 


    try { 
     // Install the custom Cache Implementation 
     HttpResponseCache.install(httpCacheDir, httpCacheSize); 
    } catch (Exception e) { 
     e.printStackTrace(); 
    } 
} 

だけのonCreateでsetContentViewの下に、次のコードを追加します。

を

cacher(); 
    cache = HttpResponseCache.getInstalled(); 
    if(cache != null) { 
     // If cache is present, flush it to the filesystem. 
     // Will be used when activity starts again. 
     cache.flush(); 
    } 

A NDここで、最終的なものはurl.openConnection線の下に、来ては、次のスニペット置く：

if (ob.isConnecting()){ 
      connection.addRequestProperty("Cache-Control", "max-age=0");} 
      else{ 
      connection.addRequestProperty("Cache-Control", "max-stale=" + 60*60*36);//In place of 36 , you can put hours for which cache is available 
      connection.setUseCaches(true); 
}