緩存設備脫機時使用的JSON響應

Question

我正在構建新聞應用程序，並且希望緩存無網絡時使用的JSON響應。我嘗試了很多方法，但它對我沒有用。

我的異步任務，我的適配器是另一面的問題時，列表加載它轉到屏幕的頂部新項目之後，它會將項目。我怎樣才能解決這個問題？

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

建立一個測試網絡連接是否可用的類。

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; 

} 
} 

創建上述類的一個對象ob。

ConnectionDetector ob=new ConnectionDetector(getApplicationContext()); 

聲明這些變量爲全局變量：

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

做一個函數cacher的（）：

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

    // Cache Size of 5MB 


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

正下方的onCreate中的setContentView，添加以下代碼：

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這裏來的最後的東西，url.openConnection線之下把下面的代碼片段：

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); 
}