自定義列表查看向上滾動然後進度條進程隱藏

Question

我發現了一些類似的問題，但無法解決問題。我有一個自定義列表視圖，其中每個項目包含一個水平進度條。但是當列表包含很多項目，並且我使用滾動條瀏覽ListView時，某些ProgressBars消失。什麼原因導致這種情況，我如何解決它？我的代碼在下面。提前致謝。

public class ScrollActivity extends Activity { 
    ListView lv; 
    // ArrayList<String> list = new ArrayList<String>(); 
    ArrayList<Url_Dto> list = new ArrayList<Url_Dto>(); 
    MyListAdapter adtf; 

    public static String prf_date_view = ""; 

    String str_start; 
    Button all_detail; 
    Button accepted_all, mainDownloadBtn; 
    Button not_shown; 
    public static SQLiteDatabase db; 
    String name; 
    File download; 

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

     list = DBAdapter.getUrl_Detail(); 
     Log.v("log_tag", "list :: " + list.size()); 
     lv = (ListView) findViewById(R.id.main_list_meet); 
     mainDownloadBtn = (Button) findViewById(R.id.not_shown); 
     adtf = new MyListAdapter(this, 0, list); 
     lv.setAdapter(adtf); 

     /*SqliteAdpter dba = SqliteAdpter 
       .getAdapterInstance(getApplicationContext()); 
     dba.createdatabase(); 
     db = dba.openDataBase();*/ 

     mainDownloadBtn.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       // Log.v("log_tag","list.toArray() "+list.size()); 
       // new DownloadFileFromURL().equals(list.toArray()); 
      } 
     }); 

    } 

    public class MyListAdapter extends ArrayAdapter<Url_Dto> { 
     private LayoutInflater mInflater; 

     ArrayList<Url_Dto> emplist = null; 
     public Activity activity; 


     public MyListAdapter(Activity activity, int layoutResourceId, 
       ArrayList<Url_Dto> emplist) { 
      super(activity, layoutResourceId, emplist); 
      this.activity = activity; 
      this.emplist = emplist; 
     } 

     /*public MyListAdapter(Context context) { 
      mInflater = LayoutInflater.from(context); 

     }*/ 

     public int getCount() { 
      return list.size(); 
     } 

     /*public Object getItem(int position) { 
      return position; 
     }*/ 

     public long getItemId(int position) { 
      return position; 
     } 

     private class ListRowViews { 
      Button cl; 
      Button dl; 
      ProgressBar pr; 
      ImageView im; 

     }; 

     public View getView(final int position, View convertView, 
       ViewGroup parent) { 
      final ListRowViews views; 

      final Url_Dto itemState = getItem(position); 

      // only recreate row if it is null 
      if (convertView == null) { 
       // store controls in tag of view so you can get them later 
       convertView = mInflater.inflate(R.layout.custome_list_view,null); 

       views = new ListRowViews(); 

       views.cl = (Button) convertView 
         .findViewById(R.id.cancle_sedual); 
       views.dl = (Button) convertView 
         .findViewById(R.id.download_sedual); 
       views.pr = (ProgressBar) convertView 
         .findViewById(R.id.listprogressbar); 
       views.im = (ImageView) convertView 
         .findViewById(R.id.list_image); 

       views.im.setImageResource(emplist.get(position).images[position]); 

       views.cl.setOnClickListener(new View.OnClickListener() { 

        @Override 
        public void onClick(View v) { 
         // TODO Auto-generated method stub 

         views.dl.setVisibility(View.VISIBLE); 
         views.cl.setVisibility(View.GONE); 

         itemState.isClicked = true; 
        } 
       }); 

       views.dl.setOnClickListener(new View.OnClickListener() { 

        @Override 
        public void onClick(View v) { 
         // TODO Auto-generated method stub 
         str_start = emplist.get(position).url_video; 
         views.dl.setVisibility(View.GONE); 
         views.cl.setVisibility(View.VISIBLE); 
         Log.v("log_tag", "str_start " + str_start); 

         // 
         // new DownloadFileFromURL().execute(str_start); 
         new DownloadFileFromURL().execute(views.pr, str_start); 
        } 
       }); 

       // store the view pointers for reuse later 
       convertView.setTag(views); 

      } else { 
       views = (ListRowViews) convertView.getTag(); 
      } 

      // you need to get the progress from list item that this view 
      // represents 
      int progress = itemState.progress; 
      views.pr.setProgress(progress); 

      views.dl.setVisibility(View.VISIBLE); 
      views.cl.setVisibility(View.VISIBLE); 

      if (itemState.isVisible) { 
       views.dl.setVisibility(View.VISIBLE); 
       views.cl.setVisibility(View.GONE); 
      } else { 
       views.dl.setVisibility(View.GONE); 
       views.cl.setVisibility(View.VISIBLE); 
      } 

      return convertView; 
     } 
    } 

    class DownloadFileFromURL extends AsyncTask<Object, String, String> { 

     int count = 0; 
     ProgressDialog dialog; 
     ProgressBar progressBar; 
     int myProgress; 

     /** 
     * Before starting background thread Show Progress Bar Dialog 
     * */ 

     @Override 
     protected void onPreExecute() { 
      super.onPreExecute(); 
      ProgressBar progressBar; 

     } 

     /** 
     * Downloading file in background thread 
     * */ 
     @Override 
     protected String doInBackground(Object... params) { 
      Log.v("log_tag", "params :::; " + params); 
      int count; 
      progressBar = (ProgressBar) params[0]; 
      try { 
       // URL url = new URL(f_url[0]); 
       URL url = new URL((String) params[1]); 
       Log.v("log_tag", "name ::: " + url); 
       name = ((String) params[1]).substring(((String) params[1]) 
         .lastIndexOf("/") + 1); 
       Log.v("log_tag", "name Substring ::: " + name); 
       URLConnection conection = url.openConnection(); 
       conection.connect(); 
       // getting file length 
       int lenghtOfFile = conection.getContentLength(); 

       // input stream to read file - with 8k buffer 
       InputStream input = new BufferedInputStream(url.openStream(), 
         8192); 
       download = new File(Environment.getExternalStorageDirectory() 
         + "/download/"); 
       if (!download.exists()) { 
        download.mkdir(); 
       } 
       String strDownloaDuRL = download + "/" + name; 
       Log.v("log_tag", " down url " + strDownloaDuRL); 
       FileOutputStream output = new FileOutputStream(strDownloaDuRL); 

       byte data[] = new byte[1024]; 

       long total = 0; 

       while ((count = input.read(data)) != -1) { 
        total += count; 
        // publishing the progress.... 
        // After this onProgressUpdate will be called 
        // publishProgress("" + (int) ((total * 100)/
        // lenghtOfFile)); 

        // writing data to file 
        progressBar 
          .setProgress((int) ((total * 100)/lenghtOfFile)); 
        output.write(data, 0, count); 
       } 
       // flushing output 
       output.flush(); 

       // closing streams 
       output.close(); 
       input.close(); 

      } catch (Exception e) { 
       Log.e("Error: ", e.getMessage()); 
      } 

      return null; 
     } 

     /** 
     * Updating progress bar 
     * */ 
     protected void onProgressUpdate(String... values) { 

      super.onProgressUpdate(values); 
      Log.v("log_tag", "progress :: " + values); 
      // setting progress percentage 
      // pDialog.setProgress(Integer.parseInt(progress[0])); 
     } 

     /** 
     * After completing background task Dismiss the progress dialog 
     * **/ 
     protected void onPostExecute(String file_url) { 

      Log.v("log", "login ::: 4::: " + download); 
      String videoPath = download + "/" + name; 
      String chpName = name; 
      Log.v("log_tag", "chpName ::::" + chpName + " videoPath " 
        + videoPath); 
      /*db.execSQL("insert into videoStatus (chapterNo,videoPath) values(\"" 
        + chpName + "\",\"" + videoPath + "\")"); 
*/ 
     } 

    } 

} 

我嘗試向上滾動時進度狀態不可見的，按鈕狀態隱藏何爲問題，以及如何解決呢？

我的錯誤假設它::

02-20 18:44:39.640: E/AndroidRuntime(4144): FATAL EXCEPTION: main 
02-20 18:44:39.640: E/AndroidRuntime(4144): java.lang.NullPointerException 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at com.example.testscrollup.ScrollActivity$MyListAdapter.getView(ScrollActivity.java:121) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.AbsListView.obtainView(AbsListView.java:1593) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.ListView.makeAndAddView(ListView.java:1782) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.ListView.fillDown(ListView.java:705) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.ListView.fillFromTop(ListView.java:762) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.ListView.layoutChildren(ListView.java:1633) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.AbsListView.onLayout(AbsListView.java:1423) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.View.layout(View.java:7175) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1047) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.View.layout(View.java:7175) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.FrameLayout.onLayout(FrameLayout.java:338) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.View.layout(View.java:7175) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1047) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.View.layout(View.java:7175) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.widget.FrameLayout.onLayout(FrameLayout.java:338) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.View.layout(View.java:7175) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.ViewRoot.performTraversals(ViewRoot.java:1146) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1865) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.os.Handler.dispatchMessage(Handler.java:99) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.os.Looper.loop(Looper.java:130) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at android.app.ActivityThread.main(ActivityThread.java:3687) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at java.lang.reflect.Method.invokeNative(Native Method) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at java.lang.reflect.Method.invoke(Method.java:507) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
02-20 18:44:39.640: E/AndroidRuntime(4144):  at dalvik.system.NativeStart.main(Native Method) 

，我用Url_dto類代碼如下::

public class Url_Dto { 
    String url_video; 
    Integer[] images = { R.drawable.alligator_sm, 
      R.drawable.bear_sm, R.drawable.bee_sm, R.drawable.bluejay_sm, 
      R.drawable.camel_sm, R.drawable.cat_sm, R.drawable.chimpanzee_sm, 
      R.drawable.chipmunk_sm, R.drawable.cheetah_sm, R.drawable.cock_sm, 
      R.drawable.cow_sm, R.drawable.coyote_sm, R.drawable.deer_sm, 
      R.drawable.dog_sm }; 
    protected boolean isClicked; 
    public int progress; 
    public boolean isVisible; 
} 

我DBADpter類給出下面給出::::

public class DBAdapter { 
    public static String url = "***** My Url ********"; 

    public static ArrayList<Url_Dto> getUrl_Detail() { 

     ArrayList<Url_Dto> fetchUrl_Detail = new ArrayList<Url_Dto>(); 
     String result = ""; 
     InputStream is = null; 

     ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); 

     // http post 
     try { 
      HttpClient httpclient = new DefaultHttpClient(); 
      HttpPost httppost = new HttpPost(url); 
      httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); 
      HttpResponse response = httpclient.execute(httppost); 
      HttpEntity entity = response.getEntity(); 
      is = entity.getContent(); 
     } catch (Exception e) { 
      Log.e("log_tag", "Error in http connection " + e.toString()); 
     } 
     // convert response to string 
     try { 
      BufferedReader reader = new BufferedReader(new InputStreamReader(
        is, "iso-8859-1"), 8); 
      StringBuilder sb = new StringBuilder(); 
      String line = null; 
      while ((line = reader.readLine()) != null) { 
       sb.append(line + "\n"); 
      } 
      is.close(); 
      result = sb.toString(); 
     } catch (Exception e) { 
      Log.e("log_tag", "Error converting result " + e.toString()); 
     } 

     // parse json data 
     try { 
      JSONObject json_obj = new JSONObject(result); 
      JSONArray j_Arr_fn = json_obj.getJSONArray("children"); 

      for (int i = 0; i < j_Arr_fn.length(); i++) { 
       JSONObject json_objs = j_Arr_fn.getJSONObject(i); 
       Url_Dto proDto = new Url_Dto(); 
       proDto.url_video = json_objs.getString("videoUrl"); 
       Log.v("log_tag", "Url :::" + json_objs.getString("videoUrl")); 
       fetchUrl_Detail.add(proDto); 
      } 

     } catch (JSONException e) { 
      Log.e("log_tag", "Error parsing data " + e.toString()); 
     } 
     return fetchUrl_Detail; 

    } 
} 

Answer 1

當您向上或向下滾動以節省內存時，android系統會重複使用行項目。

因此，當您單擊某行中的某個控件時，它將設置爲Visibility.GONE，然後當您滾動時，相同的控件在其他列表項上不可見，因爲進度欄以前設置爲不可見- 得到它？

此外，您每次顯示視圖時都會重新創建視圖，因此您正在創建新的進度欄，而不是重新使用已創建的視圖。

您只需創建一次控件，並在每次顯示控件時重置控件的可見性和狀態。

使用容器類來保存指向創建視圖的指針，所以不要每次都重新創建它們。

private class ListRowViews 
     { 
      Button c1; 
      Button d1; 
      ProgressBar pr; 

     }; 

    public View getView(final int position, View convertView, ViewGroup parent) 
    { 
     ListRowViews views; 

     final YourStateClass itemState = getItem(position); 

     //only recreate row if it is null 
     if (convertView == null) 
     { 
      //store controls in tag of view so you can get them later 
      convertView = mInflater.inflate(R.layout.custome_list_view, null); 

      views = new ListRowViews(); 

      views.cl = (Button) convertView.findViewById(R.id.cancle_sedual); 
      views.dl = (Button) convertView.findViewById(R.id.download_sedual); 
      views.pr=(ProgressBar)convertView.findViewById(R.id.listprogressbar); 

      views.cl.setOnClickListener(new View.OnClickListener() { 

          @Override 
          public void onClick(View v) { 
           // TODO Auto-generated method stub 

           views.dl.setVisibility(View.VISIBLE); 
           views.cl.setVisibility(View.GONE); 

           itemState.isClicked = true; 
          } 
         }); 

      views dl.setOnClickListener(new View.OnClickListener() { 

          @Override 
          public void onClick(View v) { 
           // TODO Auto-generated method stub 
           str_start=list.get(position).url_video; 
           views.dl.setVisibility(View.GONE); 
           views.cl.setVisibility(View.VISIBLE); 
           Log.v("log_tag","str_start "+ str_start); 

           // 
           //new DownloadFileFromURL().execute(str_start); 
           new DownloadFileFromURL().execute(pr,str_start); 
          } 
         }); 


       //store the view pointers for reuse later 
       convertView.setTag(views); 

     } 
     else 
     { 
      views = (ListRowViews)convertView.getTag();   
     }  


     //you need to get the progress from list item that this view represents 
     int progress = itemState.progress; 
     views.pr.setProgress(progress); 

     views.dl.setVisibility(View.VISIBLE); 
     views.cl.setVisibility(View.VISIBLE); 

     if (itemState.isVisible) 
     { 
      views.dl.setVisibility(View.VISIBLE); 
      views.cl.setVisibility(View.GONE); 
     } 
     else 
     { 
      views.dl.setVisibility(View.GONE); 
      views.cl.setVisibility(View.VISIBLE); 
     } 

     return convertView; 
}