14

我有一个图像视图,我写了滑动,在滑动的时候,图像是从互联网下载的,所以我想我必须在滑动之前在后台下载图像,对于我需要使用 asynctask 或服务或IntentService,所有这些都将有助于下载和存储在 data/data/mypackages 中,但在我的情况下仍然刷卡会变慢任何想法,也告诉我哪个是最好的,我是否以正确的方式调用

1.异步任务

2. 服务

3. Intent Service如下图,

我很困惑哪一个是正确的方法,因为我的问题还没有解决

这是 asynctask 代码示例片段

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);



      }

    }
4

5 回答 5

17

使用服务下载它的最佳方法就像我从服务器下载文件并放入 SD 卡一样,也使用它的通知。这是相当长的代码,但我认为是完美的,如果不明白任何事情,请到 android 开发者博客获取服务。

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());

    }
于 2011-06-13T05:02:55.960 回答
3

对于以后遇到此问题的任何人,请查看项目的 android 示例代码中使用的异步下载机制com.example.android.bitmapfun.ui.ImageGridActivity。它异步下载图像,并将它们缓存在 ImageView 中以供离线显示。人们已经将他们的代码包装在这个周围,并制作了他们自己的图像加载库。这些库使用 AsyncTask 而不是服务。异步任务预计将在几秒钟内完成他们的工作。

如果您要下载更大的内容,我建议您使用 API 9 以来可用的DownloadManager,而不是使用服务。那里有很多代码可以增加下载的弹性。

下载管理器是处理长时间运行的 HTTP 下载的系统服务。客户端可能会请求将 URI 下载到特定的目标文件。下载管理器将在后台进行下载,处理 HTTP 交互并在失败或跨连接更改和系统重新启动后重试下载。该类的实例应该通过getSystemService(String) 传递DOWNLOAD_SERVICE 来获取。通过此 API 请求下载的应用程序应为 ACTION_NOTIFICATION_CLICKED 注册一个广播接收器,以便在用户单击通知或下载 UI 中的正在运行的下载时进行适当的处​​理。请注意,应用程序必须具有 INTERNET 权限才能使用此类。

于 2013-03-26T12:46:58.400 回答
2

你可能过度设计了这个。我已经实现了动态加载图像的滑动,我只是使用了一个简单的实用程序类,它通过静态方法调用为我完成了这一切。试试这个类:

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();
    }

}

这就是你所需要的。然后,当您需要加载图像时,您调用:

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

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

于 2011-06-10T10:03:58.533 回答
0

我们在这里使用最新的架构组件。我们为一些表示下载状态的标志创建了一些带有实时数据的观察者。在服务中,我们下载图像并完成更新实时数据,以便自动调用观察者方法

于 2018-08-11T08:38:01.987 回答
0

使用截击。使用凌空网络图像视图你可以做到这一点

于 2018-08-03T10:06:08.803 回答