小贝子编程

我如何正确使用异步任务



我正在开发一个Android应用程序，但是Asynctask和Looper给我带来了更多的问题，我不明白如何解决这个问题......这是我的主要活动：

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
public class MainActivity extends Activity {
 private ProgressDialog progress = null;
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);  

  //Check if the connectivity is available   
  CheckConnectivity check = new CheckConnectivity();
  Boolean conn = check.checkNow(this.getApplicationContext());
  //if connectivity is available
  if(conn == true){
   //Create the action bar
   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {  
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
    ActionBar actionBar = getActionBar();
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setDisplayHomeAsUpEnabled(false);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#0170a5")));
   }
   setContentView(R.layout.activity_main);
   GetNews getNews = new GetNews();
   getNews.execute();
  }else{
      connectivityMessage("Nessuna connessione presente, assicurati di avere il traffico dati oppure il Wi-Fi attivato e riprova."); 
  }
 } 
/******************************************************************************************************/
 private class GetNews extends AsyncTask<Void, Void, String>{
   @Override
   protected String doInBackground(Void... params) {
    Looper.prepare(); 
    ReadServer read = new ReadServer();
    String result = read.readserver("list_news","homepage");
    return result;
   }
   @Override
   protected void onCancelled() {
    super.onCancelled();
   }
   @Override
   protected void onPreExecute() {
    progress = ProgressDialog.show(
    MainActivity.this, null, "Caricamento notizie...");
    super.onPreExecute();
  }
    @Override
    protected void onPostExecute(String result) {
    super.onPostExecute(result);
    try {
     String url_img = null;
     String path = "http://www.MYPATH.it";
     TableLayout MainTable = (TableLayout) findViewById(R.id.main_table);
     JSONArray Jobj = new JSONArray(result);
     for (int i = 0; i < Jobj.length(); i++) {
     TableRow row = new TableRow(getApplicationContext());
     row.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));

     JSONObject news_preview = Jobj.getJSONObject(i);
     Integer news_id = news_preview.getInt("id_articolo");
     String news_title = news_preview.getString("titolo");
     String news_image = news_preview.getString("immagine");
     // Check if image url is relative or absolute
     Pattern p = Pattern.compile("^(https?|ftp|file)://[-a-zA-Z0-9+&@#/%?=~_|!:,.;]*[-a-zA-Z0-9+&@#/%=~_|]");
     Matcher m = p.matcher(news_image);
     if (m.matches() == false) {
         url_img = path + news_image;
     } else if (m.matches() == true) {
        url_img = news_image;
     }
     // Call Html Parser to parse text
     HtmlParser parsed_string = new HtmlParser();
     Spanned title_nohtml = parsed_string.htmlparser(news_title);
     final ImageView img = new ImageView(getApplicationContext());
     final TextView txt = new TextView(getApplicationContext());
     LayoutParams params = new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
     img.setAdjustViewBounds(true);
     Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL(url_img).getContent());
     Bitmap resized = null;
     int screenLayout = getApplicationContext().getResources().getConfiguration().screenLayout;
     screenLayout &= Configuration.SCREENLAYOUT_SIZE_MASK;
     switch (screenLayout) {
      case Configuration.SCREENLAYOUT_SIZE_SMALL:
       row.setPadding(0, 7, 2, 7);   
       resized = Bitmap.createScaledBitmap(bitmap, 70, 70, true);
       txt.setTextSize(18);
     break;
      case Configuration.SCREENLAYOUT_SIZE_NORMAL:
       row.setPadding(0, 14, 2, 14);
       resized = Bitmap.createScaledBitmap(bitmap, 140, 140, true);
       txt.setTextSize(18);
      break;
      case Configuration.SCREENLAYOUT_SIZE_LARGE:
       row.setPadding(0, 14, 2, 14);
       resized = Bitmap.createScaledBitmap(bitmap, 200, 200, true);
       txt.setTextSize(24);
      break;
      case Configuration.SCREENLAYOUT_SIZE_XLARGE:
       row.setPadding(0, 14, 2, 14);
       resized = Bitmap.createScaledBitmap(bitmap, 200, 200, true);
       txt.setTextSize(24);
      break;
      default:
      break;
     }
     img.setImageBitmap(resized);
     txt.setGravity(Gravity.LEFT | Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL);
     txt.setLayoutParams(params);
     txt.setBackgroundColor(Color.WHITE);
     txt.setTypeface(null, Typeface.BOLD);
     txt.setTextColor(Color.BLACK);
     txt.setId(news_id);
     txt.setText(title_nohtml);
     txt.setClickable(true);
     row.addView(img);
     row.addView(txt);
     MainTable.addView(row);
     txt.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
       Intent intent = new Intent(MainActivity.this, NewsDetail.class);
       Bundle extras = new Bundle();
       extras.putInt("id_news", txt.getId());
       intent.putExtras(extras);
       startActivity(intent);
      }
     });
    }
   }catch (Exception e) {
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this);
     alertDialog.setTitle("Si è verificato un errore");
     alertDialog.setMessage("Errore 001" + "n" + "Non è stato possibile soddisfare la tua richiesta, riprova più tardi.");
     alertDialog.show();
    }
    progress.dismiss();
    Looper.loop();
    Looper.getMainLooper().quitSafely();
    change();
   }
   @Override
    protected void onProgressUpdate(Void... values) {
     super.onProgressUpdate(values);
   }
  }
 /******************************************************************************************************/
 @Override
 public void onStart() {
  super.onStart();
  Tracker tracker = GoogleAnalytics.getInstance(this).getTracker("UA-49974758-1");
  tracker.set(Fields.SCREEN_NAME, "Visualizzazione prima pagina");
  tracker.send(MapBuilder.createAppView().set(Fields.customDimension(1), "Premium").build());
 }
 /******************************************************************************************************/
 public void change(){
  ChangeLog cl = new ChangeLog(this);
  if (cl.firstRun())
  cl.getLogDialog().show();
}
 /******************************************************************************************************/
 @Override
 public void onDestroy() {
  super.onDestroy();
  if ( progress!=null && progress.isShowing() ){
      progress.cancel();
  }
 }
/******************************************************************************************************/
 @Override
 public void onPause() {
  super.onPause();
  if ( progress!=null && progress.isShowing() ){
      progress.cancel();
  }
 }

*****编辑*****

视频库代码 ：

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
public class VideoGallery extends Activity {
 private ProgressDialog progress = null;

 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  //Check if the connectivity is available   
  CheckConnectivity check = new CheckConnectivity();
  Boolean conn = check.checkNow(this.getApplicationContext());
  //if connectivity is available
  if(conn == true){
   //Create the action bar
   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {  
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
    ActionBar actionBar = getActionBar();
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setDisplayHomeAsUpEnabled(false);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#0170a5")));
   }
   setContentView(R.layout.activity_main);
   GetVideo getVideo = new GetVideo();
   getVideo.execute();
  }else{
     connectivityMessage("Nessuna connessione presente, assicurati di avere il traffico dati oppure il Wi-Fi attivato e riprova."); 
  } 
 }
/************************************************************************/
 private class GetVideo extends AsyncTask<Void, Void, String>{
   @Override
   protected String doInBackground(Void... params) {
    Looper.prepare();  <---- LINE 86
    ReadServer read = new ReadServer();
    String result = read.readserver("id_gallery", "gall_video");
    return result;
   }
   @Override
   protected void onCancelled() {
    super.onCancelled();
   }
   @Override
   protected void onPreExecute() {
    progress = ProgressDialog.show(
    VideoGallery.this, null, "Caricamento video...");
    super.onPreExecute();
  }
    @Override
    protected void onPostExecute(String result) {
    super.onPostExecute(result);
    try{      
     TableLayout MainTable = (TableLayout)findViewById(R.id.main_table); 
     JSONArray Jobj = new JSONArray(result);
     String url_img = null;
     String url_video = null;
     for (int i = 0; i < Jobj.length(); i++){
      TableRow row = new TableRow(getApplicationContext()); 
      row.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));

      JSONObject list_video = Jobj.getJSONObject(i);
      Integer video_id = list_video.getInt("id_video");
      String video_title = list_video.getString("nome_video");
      String video_image = list_video.getString("video_img");
      String video_url = list_video.getString("url_video");
      Pattern p = Pattern.compile("^(https?|ftp|file)://[-a-zA-Z0-9+&@#/%?=~_|!:,.;]*[-a-zA-Z0-9+&@#/%=~_|]");
      Matcher m = p.matcher(video_image);
      Pattern v = Pattern.compile("^/video/[-a-zA-Z0-9+&@#/%?=~_|!:,.;]*[-a-zA-Z0-9+&@#/%=~_|]");
      Matcher vm = v.matcher(video_url);
      //Path video
      if(vm.matches() == false){
       url_video = path_youtube+video_url;
      }else if(vm.matches() == true){
       url_video = path_an_tv+video_url;
      }
      //Path image
      if(m.matches() == false){
       url_img = path+video_image;
      }else if(m.matches() == true){
       url_img = video_image;
      }
      final ImageView img = new ImageView(getApplicationContext());
      final TextView txt = new TextView(getApplicationContext());
      LayoutParams params;
      img.setAdjustViewBounds(true); 
      img.setScaleType(ImageView.ScaleType.CENTER_CROP);
      txt.setGravity(Gravity.LEFT | Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL );
      Bitmap bitmap = BitmapFactory.decodeStream((InputStream)new URL(url_img).getContent());
      Bitmap resized = null;
      int screenLayout = getApplicationContext().getResources().getConfiguration().screenLayout;
      screenLayout &= Configuration.SCREENLAYOUT_SIZE_MASK;
      switch (screenLayout) {
       case Configuration.SCREENLAYOUT_SIZE_SMALL:
        row.setPadding(0, 7, 0, 7);
        resized = Bitmap.createScaledBitmap(bitmap, 70, 70, true);
        params =  new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, 70);
        txt.setLayoutParams(params); 
        txt.setTextSize(18); 
      break;
       case Configuration.SCREENLAYOUT_SIZE_NORMAL:
        row.setPadding(0, 14, 0, 14);
        resized = Bitmap.createScaledBitmap(bitmap, 140, 140, true);
        params =  new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, 140);
        txt.setLayoutParams(params); 
        txt.setTextSize(18);  
      break;
       case Configuration.SCREENLAYOUT_SIZE_LARGE:
       row.setPadding(0, 14, 0, 14);
       resized = Bitmap.createScaledBitmap(bitmap, 200, 200, true);
       params =  new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, 200);
       txt.setLayoutParams(params);
       txt.setTextSize(24);
       break;
       case Configuration.SCREENLAYOUT_SIZE_XLARGE:
        row.setPadding(0, 14, 0, 14);
        resized = Bitmap.createScaledBitmap(bitmap, 200, 200, true); 
        params =  new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, 200);
        txt.setLayoutParams(params);
        txt.setTextSize(24);
       break;
       default:
       break;
      }
      txt.setBackgroundColor(Color.WHITE);
      txt.setTypeface(null, Typeface.BOLD); 
      txt.setTextColor(Color.BLACK); 
      txt.setId(video_id); 
      txt.setTag(url_video); 
      txt.setText(video_title); 
      txt.setClickable(true);         
      img.setImageBitmap(resized);
      row.addView(img);
      row.addView(txt); 
      MainTable.addView(row);
      txt.setOnClickListener(new OnClickListener(){
       public void onClick(View v) {
        startActivity(new Intent(Intent.ACTION_VIEW,Uri.parse((String) txt.getTag())));
       }
      });
     }
    }catch(Exception e){
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(VideoGallery.this);
     alertDialog.setTitle("Si è verificato un errore");
     alertDialog.setMessage("Errore 001" +"n"+"Non è stato possibile soddisfare la tua richiesta, riprova più tardi.");
     alertDialog.show();        
    } 
    progress.dismiss();
    Looper.loop();
    Looper.getMainLooper().quitSafely();
   }
   @Override
    protected void onProgressUpdate(Void... values) {
     super.onProgressUpdate(values);
   }
  }
/******************************************************************************************************/
 @Override
 public void onStart() {
  super.onStart();
  Tracker tracker = GoogleAnalytics.getInstance(this).getTracker("UA-49974758-1");
  tracker.set(Fields.SCREEN_NAME, "Visualizzazione video");
  tracker.send(MapBuilder.createAppView().set(Fields.customDimension(1), "Premium").build());
 }
/******************************************************************************************************/
 @Override
 public void onDestroy() {
  super.onDestroy();
  if ( progress!=null && progress.isShowing() ){
      progress.cancel();
  }
 }
/******************************************************************************************************/
 @Override
 public void onPause() {
  super.onPause();
  if ( progress!=null && progress.isShowing() ){
      progress.cancel();
  }
 }

当我将活动更改为另一个再次包含异步任务的活动时，发生了错误：

11-14 11:49:18.196: E/AndroidRuntime(18749): FATAL EXCEPTION: AsyncTask #1
11-14 11:49:18.196: E/AndroidRuntime(18749): java.lang.RuntimeException: An error occured while executing doInBackground()
11-14 11:49:18.196: E/AndroidRuntime(18749):    at android.os.AsyncTask$3.done(AsyncTask.java:299)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.util.concurrent.FutureTask.run(FutureTask.java:239)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at java.lang.Thread.run(Thread.java:841)
11-14 11:49:18.196: E/AndroidRuntime(18749): Caused by: java.lang.RuntimeException: Only one Looper may be created per thread
11-14 11:49:18.196: E/AndroidRuntime(18749):    at android.os.Looper.prepare(Looper.java:78)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at android.os.Looper.prepare(Looper.java:73)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at com.miaapplicazione.VideoGallery$GetVideo.doInBackground(VideoGallery.java:86)
11-14 11:49:18.196: E/AndroidRuntime(18749):    at com.miaapplicazione.VideoGallery$GetVideo.doInBackground(VideoGallery.java:1)

编辑 2 ****

如果我删除Looper.prepare（）;在视频库中发生另一个错误：

11-14 12:01:48.357: E/AndroidRuntime(20476): FATAL EXCEPTION: AsyncTask #2
11-14 12:01:48.357: E/AndroidRuntime(20476): java.lang.RuntimeException: An error occured while executing doInBackground()
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.os.AsyncTask$3.done(AsyncTask.java:299)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.FutureTask.run(FutureTask.java:239)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.lang.Thread.run(Thread.java:841)
11-14 12:01:48.357: E/AndroidRuntime(20476): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.os.Handler.<init>(Handler.java:197)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.os.Handler.<init>(Handler.java:111)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.app.Activity.<init>(Activity.java:759)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at com.alessandrianews.ReadServer.<init>(ReadServer.java:17)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at com.alessandrianews.VideoGallery$GetVideo.doInBackground(VideoGallery.java:86)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at com.alessandrianews.VideoGallery$GetVideo.doInBackground(VideoGallery.java:1)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
11-14 12:01:48.357: E/AndroidRuntime(20476):    at java.util.concurrent.FutureTask.run(FutureTask.java:234)
11-14 12:01:48.357: E/AndroidRuntime(20476):    ... 4 more

我如何解决这个问题？我阅读了所有其他问题，但解决方案对我没有帮助。

如果你想

使用AsyncTask，那就使用它，你不应该把它和Lopper混用。

protected Integer doInBackground(Void... params) {}

已经在后台线程上工作，没有理由打电话给 Lopper，为了什么？

如果您的应用程序需要执行某种长时间的计算，那么 AsyncTask 是非常好的工具，因为提供了在 UI 线程上工作的方法，并允许使用一些工作进度更新 UI，因为每个将使用您的应用程序的用户都应该知道应用程序"做某事"（当它需要超过 2-5 秒时）。

此外，它是通用的，并提供一些好处。

如果您不需要更新 UI，只需使用例如处理程序。

所以删除Looper.prepare();

尝试添加：

if (Looper.myLooper() == null) Looper.prepare;

它对我有用

相关内容

  • 没有找到相关文章

最新更新


热门标签：

javascript python java c# php android html jquery c++ css ios sql mysql arrays asp.net json python-3.x ruby-on-rails .net sql-server django objective-c excel regex ruby linux ajax iphone xml vba spring asp.net-mvc database wordpress string postgresql wpf windows xcode bash git oracle list vb.net multithreading eclipse algorithm macos powershell visual-studio image forms numpy scala function api selenium