Android中的背景图片下载需要帮助吗？

Question

我有一个图像视图,我写过刷卡,在刷卡的时候,图像从互联网上下载,所以我想我必须在刷卡之前在后台下载图像,因为我需要使用asynctask或Service或IntentService,所有这些都有助于下载和存储在数据/数据/ mypackages中,但仍然在我的情况下刷卡任何想法,也告诉我哪一个是最好的,是我正在以正确的方式调用

asynctask

2.服务

3.意向服务如下图所示,

我很困惑哪一个是正确的方法,因为我的问题仍未解决

这是asynctask代码示例代码段

public class Demo extends Activity {

  @Override

  public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

       new FirstTask().execute(); // calling Asynctask here

  }

}

异步任务代码

private class FirstTask extends AsyncTask<Void, Void, Void> {
        private final ProgressDialog dialog = new ProgressDialog(Catalogue.this);
        int temp = 0;

        // can use UI thread here
        protected void onPreExecute() {
            this.dialog.setMessage("Loading...");
            this.dialog.setCancelable(false);
            //this.dialog.show();
            System.gc();
            Toast.makeText(Catalogue.this, "My Async  Created",
                    Toast.LENGTH_LONG).show();
        }

        @Override
        protected Void doInBackground(Void... params) {
            Looper.prepare();  
            try {

                myddownloadmethod();// calling my download method

            } catch (Exception e) {
                Util.trace("Error in Async"+e.getMessage());

            }
              Looper.loop();

            return null;
        }

        protected void onPostExecute(Void result) {

            if (this.dialog.isShowing()) {
                Toast.makeText(Catalogue.this, "My Async destroyed",
                        Toast.LENGTH_LONG).show();
                Toast.makeText(Catalogue.this, "count" + temp,
                        Toast.LENGTH_LONG).show();
                this.dialog.dismiss();
            }
        }
    }

这是我的服务

public class MyService extends Service implements Runnable

{      @Override

        public void onCreate() {

                super.onCreate();

                Thread mythread = new Thread(this);

                mythread.start();

        }



        public void run() {

                Looper.prepare();  

                try {

                        myddownloadmethod();// calling my download method

                } catch (Exception e1) {

                        // TODO Auto-generated catch block

                        e1.printStackTrace();

                }

                Looper.loop();

        }



        @Override
        public IBinder onBind(Intent intent) {

                // TODO Auto-generated method stub

                return null;

        }



}



Invoking Service  

public class ServicesDemo extends Activity {    

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

      startService(new Intent(this, MyService.class));


  }

}

这是IntentService代码

public class Downloader extends IntentService {

    public Downloader() {
        super("Downloader");
    }

    @Override
    public void onCreate() {
        super.onCreate();


    }

    @Override
    public void onDestroy() {
        super.onDestroy();

            }

    @Override   
    public void onHandleIntent(Intent i) {

        try {
             myddownloadmethod();// calling my download method
        } catch (Exception e1) {
            // TODO Auto-generated catch block
            Log.d("Error",e1.getMessage());
        }

    }
}

从MyActivity调用IntentService

public class ServicesDemo extends Activity {    
      @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Intent i1=new Intent(this, Downloader.class);
        startService(i1);



      }

    }

Answer 1

使用像我从服务器下载文件并放入SD卡的服务下载它的最佳方式也使用通知.它是相当长的代码,但我认为完美的一个,如果不明白任何事情,那么请去android开发者博客的服务.

public class DownloadService extends Service{

     SharedPreferences preferences;

    private static final String DOCUMENT_VIEW_STATE_PREFERENCES = "DjvuDocumentViewState";

      private Looper mServiceLooper;
      private ServiceHandler mServiceHandler;
      private NotificationManager mNM;
      String downloadUrl;
      public static boolean serviceState=false;

      // Handler that receives messages from the thread
      private final class ServiceHandler extends Handler {
          public ServiceHandler(Looper looper) {
              super(looper);
          }
          @Override
          public void handleMessage(Message msg) {
              downloadFile();
              showNotification(getResources().getString(R.string.notification_catalog_downloaded),"VVS");
              stopSelf(msg.arg1);
          }
      }


    @Override
        public void onCreate() {
            serviceState=true;
            mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
            HandlerThread thread = new HandlerThread("ServiceStartArguments",1);
            thread.start();

            // Get the HandlerThread's Looper and use it for our Handler 
            mServiceLooper = thread.getLooper();
            mServiceHandler = new ServiceHandler(mServiceLooper);

        }



     @Override
        public int onStartCommand(Intent intent, int flags, int startId) {
             Log.d("SERVICE-ONCOMMAND","onStartCommand");  

               Bundle extra = intent.getExtras();
               if(extra != null){
                   String downloadUrl = extra.getString("downloadUrl");
                   Log.d("URL",downloadUrl);

                   this.downloadUrl=downloadUrl;
               }

              Message msg = mServiceHandler.obtainMessage();
              msg.arg1 = startId;
              mServiceHandler.sendMessage(msg);

              // If we get killed, after returning from here, restart
              return START_STICKY;
          }



     @Override
          public void onDestroy() {

             Log.d("SERVICE-DESTROY","DESTORY");
             serviceState=false;
            //Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show(); 
          }


     @Override
      public IBinder onBind(Intent intent) {
          // We don't provide binding, so return null
          return null;
      }


      public void downloadFile(){

            downloadFile(this.downloadUrl,fileName);


      }



        void showNotification(String message,String title) {
        // In this sample, we'll use the same text for the ticker and the expanded notification
        CharSequence text = message;

        // Set the icon, scrolling text and timestamp
       Notification notification = new Notification(R.drawable.icon, "vvs",
                System.currentTimeMillis());
        notification.flags |= Notification.FLAG_AUTO_CANCEL;
        Intent intent = new Intent(this, HomeScreenActivity.class);
        intent.setFlags (Intent.FLAG_ACTIVITY_CLEAR_TOP);
         //The PendingIntent to launch our activity if the user selects this notification
        PendingIntent contentIntent = PendingIntent.getActivity(this.getBaseContext(), 0,
              intent, PendingIntent.FLAG_CANCEL_CURRENT);

        // Set the info for the views that show in the notification panel.
        notification.setLatestEventInfo(this, title,
                      text, contentIntent);
        // Send the notification.
        // We use a layout id because it is a unique number.  We use it later to cancel.
        mNM.notify(R.string.app_name, notification);
    }

  public void downloadFile(String fileURL, String fileName) {

    StatFs stat_fs = new StatFs(Environment.getExternalStorageDirectory().getPath());
    double avail_sd_space = (double)stat_fs.getAvailableBlocks() *(double)stat_fs.getBlockSize();
    //double GB_Available = (avail_sd_space / 1073741824);
    double MB_Available = (avail_sd_space / 10485783);
    //System.out.println("Available MB : " + MB_Available);
    Log.d("MB",""+MB_Available);
   try {
        File root =new File(Environment.getExternalStorageDirectory()+"/vvveksperten");
        if(root.exists() && root.isDirectory()) {

        }else{
            root.mkdir();
        }
        Log.d("CURRENT PATH",root.getPath());
        URL u = new URL(fileURL);
        HttpURLConnection c = (HttpURLConnection) u.openConnection();
        c.setRequestMethod("GET");
        c.setDoOutput(true);
        c.connect();
          int fileSize  = c.getContentLength()/1048576;
          Log.d("FILESIZE",""+fileSize);
          if(MB_Available <= fileSize ){
               this.showNotification(getResources().getString(R.string.notification_no_memory),getResources().getString(R.string.notification_error));
              c.disconnect();
              return;
          } 

        FileOutputStream f = new FileOutputStream(new File(root.getPath(), fileName));

        InputStream in = c.getInputStream();


        byte[] buffer = new byte[1024];
        int len1 = 0;
        while ((len1 = in.read(buffer)) > 0) {
            f.write(buffer, 0, len1);
        }
        f.close();
        File file = new File(root.getAbsolutePath() + "/" + "some.pdf");
        if(file.exists()){
            file.delete();
            Log.d("FILE-DELETE","YES");
        }else{
            Log.d("FILE-DELETE","NO");
        }
        File from =new File(root.getAbsolutePath() + "/" + fileName);
        File to = new File(root.getAbsolutePath() + "/" + "some.pdf");


        } catch (Exception e) {
        Log.d("Downloader", e.getMessage());

    }

Answer 2

您可能对此进行了过度设计。我已经实现了动态加载图像的滑动，我只是使用一个简单的实用程序类，它通过静态方法调用为我完成这一切。试试这个课程：

package com.beget.consumer.util;

/*
 Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.    
*/
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.net.MalformedURLException;
import java.util.HashMap;
import java.util.Map;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public class DrawableLoader {
    private final Map<String, Drawable> drawableMap;
    private WeakReference<ImageView> imageViewReference;

    public DrawableLoader() {
        drawableMap = new HashMap<String, Drawable>();
    }

    public Drawable fetchDrawable(String urlString) {
        if (drawableMap.containsKey(urlString)) {
            return drawableMap.get(urlString);
        }

        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
        try {
            InputStream is = fetch(urlString);
            Drawable drawable = Drawable.createFromStream(is, "src");
            drawableMap.put(urlString, drawable);
            Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                    + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                    + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
            return drawable;
        } catch (MalformedURLException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        } catch (IOException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        }
    }

    public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {

        imageViewReference = new WeakReference<ImageView>(imageView);

        if (drawableMap.containsKey(urlString)) {
            imageViewReference.get().setImageDrawable(drawableMap.get(urlString));
        }

        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message message) {
                imageViewReference.get().setImageDrawable((Drawable) message.obj);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                //TODO : set imageView to a "pending" image
                Drawable drawable = fetchDrawable(urlString);
                Message message = handler.obtainMessage(1, drawable);
                handler.sendMessage(message);
            }
        };
        thread.start();
    }

    private InputStream fetch(String urlString) throws MalformedURLException, IOException {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet request = new HttpGet(urlString);
        HttpResponse response = httpClient.execute(request);
        return response.getEntity().getContent();
    }

}

这就是您所需要的。然后当你需要加载图像时，你调用：

fetchDrawableOnThread("http://path/to/your/image.jpg", yourImageViewReference);

就是这样。
如果您有来自 JSON 对象的 URL，请将 URL 解析为字符串：
String url = jsonObj.getString("url"); 然后调用fetchDrawableOnThread(url, yourImageViewReference);