自定義無盡ListView Android

Question

我試圖做無盡的適配器，但無法完成它，因此我的應用程序崩潰。 我試圖做的是，最初我想在列表視圖中加載10項，並在listview結束時添加foorterview。如果用戶點擊footerview比在列表視圖中加載10項更多的項目。

但是，當我開始該活動只有footerview出現，並在幾秒鐘後應用程序崩潰。 我已經發布了以下相關代碼：

int questionsPerPage = 10; 
boolean loadingMore = false; 
ArrayList<DataHolder> myquestionsResults; 
QuestionListViewAdapter adapter; 

//in onCreate 
lv = (ListView) findViewById(R.id.lv_questions); 
    // add the footer before adding the adapter, else the footer will not 
    // load! 
    View footerView = ((LayoutInflater) this 
      .getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(
      R.layout.listfooter, null, false); 
    footerView.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
      Thread thread = new Thread(null, loadMoreListItems); 
      thread.start(); 
     } 
    }); 
    lv.addFooterView(footerView); 
    myquestionsResults = new ArrayList<DataHolder>(); 
    adapter = new QuestionListViewAdapter(this, myquestionsResults); 
    lv.setAdapter(adapter); 
    lv.setOnItemClickListener(new OnItemClickListener() { 

     public void onItemClick(AdapterView<?> a, View v, int position, 
       long id) { 
      Object o = lv.getItemAtPosition(position); 
      DataHolder fullObject = (DataHolder) o; 
      Intent intent = new Intent(getApplicationContext(), 
        ViewMyQuestion.class); 
      intent.putExtra("id", fullObject.getId()); 
      startActivity(intent); 

     } 

    }); 

    // Load the first 10 items 
    Thread thread = new Thread(null, loadMoreListItems); 
    thread.start(); 
}// End of onCreate 

private ArrayList<DataHolder> GetMyQuestionsResult() { 
    ArrayList<DataHolder> myquestionInfo = new ArrayList<DataHolder>(); 
    HashMap<String, String> hm = new HashMap<String, String>(); 
    db = new DatabaseHandler(getApplicationContext()); 
    db.getReadableDatabase(); 
    hm = db.getUserDetails(); 
    db.close(); 
    String un = hm.get("username"); 

    uf = new UserFunctions(); 
    JSONArray json = uf.getQuestionsByUsername(un); 
    int x = json.length(); 
    try { 
     if (x > 0) { 
      for (int i = 0; i < x; i++) { 
       ja = json.getJSONArray(i); 
       id = ja.getString(0); 
       userName = ja.getString(1); 
       question = ja.getString(2); 
       tag1 = ja.getString(3); 
       tag2 = ja.getString(4); 
       tag3 = ja.getString(5); 
       posted_on = ja.getString(6); 
       DataHolder qih = new DataHolder(); 
       qih.setId(id); 
       qih.setUserName(userName); 
       qih.setQuestion(question); 
       qih.setTag1(tag1); 
       qih.setTag2(tag2); 
       qih.setTag3(tag3); 
       qih.setQuestionPostedOn(posted_on); 
       myquestionInfo.add(qih); 
      } 
     } 
    } catch (Exception e) { 
     e.printStackTrace(); 

    } 
    return myquestionInfo; 
} 
// Runnable to load the items 
private Runnable loadMoreListItems = new Runnable() { 
    public void run() { 
     // Set flag so we cant load new items 2 at the same time 
     loadingMore = true; 

     // Reset the array that holds the new items 


     // Get 10 new listitems 
     for (int i = 0; i < questionsPerPage; i++) { 
      // Fill the item with some bogus information 
      myquestionsResults.add(GetMyQuestionsResult().get(i)); 

     } 

     // Done! now continue on the UI thread 
     runOnUiThread(returnRes); 

    } 
}; 

// Since we cant update our UI from a thread this Runnable takes care of 
// that! 
private Runnable returnRes = new Runnable() { 
    @SuppressWarnings("unchecked") 
    public void run() { 

     // Tell to the adapter that changes have been made, this will cause 
     // the list to refresh 
     ((BaseAdapter) lv.getAdapter()).notifyDataSetChanged(); 

     // Done loading more. 
     loadingMore = false; 
    } 
}; 

下面是我的logcat消息：

08-27 06:00:03.799: E/AndroidRuntime(280): FATAL EXCEPTION: main 
08-27 06:00:03.799: E/AndroidRuntime(280): java.lang.ClassCastException: android.widget.HeaderViewListAdapter 
08-27 06:00:03.799: E/AndroidRuntime(280): at com.vervecoders.cuqu.MyQuestions$3.run(MyQuestions.java:275) 
08-27 06:00:03.799: E/AndroidRuntime(280): at android.os.Handler.handleCallback(Handler.java:587) 
08-27 06:00:03.799: E/AndroidRuntime(280): at android.os.Handler.dispatchMessage(Handler.java:92) 
08-27 06:00:03.799: E/AndroidRuntime(280): at android.os.Looper.loop(Looper.java:123) 
08-27 06:00:03.799: E/AndroidRuntime(280): at android.app.ActivityThread.main(ActivityThread.java:4627) 
08-27 06:00:03.799: E/AndroidRuntime(280): at java.lang.reflect.Method.invokeNative(Native Method) 
08-27 06:00:03.799: E/AndroidRuntime(280): at java.lang.reflect.Method.invoke(Method.java:521) 
08-27 06:00:03.799: E/AndroidRuntime(280): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
08-27 06:00:03.799: E/AndroidRuntime(280): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
08-27 06:00:03.799: E/AndroidRuntime(280): at dalvik.system.NativeStart.main(Native Method) 

---

更新代碼後墜毀again.Following是新的logcat消息：

08-27 07:38:47.751: I/dalvikvm(349): "main" prio=5 tid=1 RUNNABLE 
08-27 07:38:47.751: I/dalvikvm(349): | group="main" sCount=0 dsCount=0 s=N obj=0x4001d8e0 self=0xccb0 
08-27 07:38:47.751: I/dalvikvm(349): | sysTid=349 nice=0 sched=0/0 cgrp=default handle=-1345026008 
08-27 07:38:47.751: I/dalvikvm(349): | schedstat=(33038897911 15262681460 1352) 
08-27 07:38:47.751: I/dalvikvm(349): at java.util.ArrayList.add(ArrayList.java:~123) 
08-27 07:38:47.765: I/dalvikvm(349): at com.vervecoders.cuqu.MyQuestions$3.run(MyQuestions.java:267) 
08-27 07:38:47.765: I/dalvikvm(349): at android.os.Handler.handleCallback(Handler.java:587) 
08-27 07:38:47.771: I/dalvikvm(349): at android.os.Handler.dispatchMessage(Handler.java:92) 
08-27 07:38:47.771: I/dalvikvm(349): at android.os.Looper.loop(Looper.java:123) 
08-27 07:38:47.771: I/dalvikvm(349): at android.app.ActivityThread.main(ActivityThread.java:4627) 
08-27 07:38:47.785: I/dalvikvm(349): at java.lang.reflect.Method.invokeNative(Native Method) 
08-27 07:38:47.785: I/dalvikvm(349): at java.lang.reflect.Method.invoke(Method.java:521) 
08-27 07:38:47.785: I/dalvikvm(349): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
08-27 07:38:47.785: I/dalvikvm(349): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
08-27 07:38:47.785: I/dalvikvm(349): at dalvik.system.NativeStart.main(Native Method) 
08-27 07:38:47.811: D/AndroidRuntime(349): Shutting down VM 
08-27 07:38:47.811: W/dalvikvm(349): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
08-27 07:38:47.845: E/AndroidRuntime(349): FATAL EXCEPTION: main 
08-27 07:38:47.845: E/AndroidRuntime(349): java.lang.OutOfMemoryError 
08-27 07:38:47.845: E/AndroidRuntime(349): at java.util.ArrayList.add(ArrayList.java:123) 
08-27 07:38:47.845: E/AndroidRuntime(349): at com.vervecoders.cuqu.MyQuestions$3.run(MyQuestions.java:267) 
08-27 07:38:47.845: E/AndroidRuntime(349): at android.os.Handler.handleCallback(Handler.java:587) 
08-27 07:38:47.845: E/AndroidRuntime(349): at android.os.Handler.dispatchMessage(Handler.java:92) 
08-27 07:38:47.845: E/AndroidRuntime(349): at android.os.Looper.loop(Looper.java:123) 
08-27 07:38:47.845: E/AndroidRuntime(349): at android.app.ActivityThread.main(ActivityThread.java:4627) 
08-27 07:38:47.845: E/AndroidRuntime(349): at java.lang.reflect.Method.invokeNative(Native Method) 
08-27 07:38:47.845: E/AndroidRuntime(349): at java.lang.reflect.Method.invoke(Method.java:521) 
08-27 07:38:47.845: E/AndroidRuntime(349): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
08-27 07:38:47.845: E/AndroidRuntime(349): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
08-27 07:38:47.845: E/AndroidRuntime(349): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

((ArrayList<DataHolder>) lv.getAdapter()).add(myquestionsResults.get(i)); 

爲什麼要將適配器轉換爲ArrayList？這可能導致ClassCastException嘗試將新項目添加到myquestionsResults，然後通知適配器。更好的是，你可以在你的QuestionListViewAdapter的實現中添加一個方法add（）（或者甚至addAll（）），它將把這些項添加到列表中並調用notifyDataSetChanged（）。在這種情況下，您可以使適配器成爲一個成員變量並直接使用它，而不是從緩存的ListView中獲取它。