在SQLite中使用Asynctask和Listview

Question

我使用AsyncTask查詢SQLite數據庫-聯系人。

當我在android模擬器上運行該代碼時，它工作正常（可能是因為我添加的聯系人減少了），但是當我在移動設備上運行（它有大約500個聯系人）時，應用運行緩慢。

任何幫助，將不勝感激。 謝謝。

代碼如下。

      private class loadMoreListView extends AsyncTask<Void, Void, Void> {

            ArrayList<Contact> contactsx = new ArrayList<Contact>();
            @Override
            protected void onPreExecute() {
                pDialog = new ProgressDialog(MainActivity.this);
                pDialog.setMessage("Please wait..");
                pDialog.setIndeterminate(true);
                pDialog.setCancelable(false);
                pDialog.show();
                lv = (ListView) findViewById(R.id.blacklist);

            }

            @Override
            protected void onPostExecute(Void unused) {
                // closing progress dialog

                lv.setAdapter(adapter);

                pDialog.dismiss();
            }

            @Override
            protected Void doInBackground(Void... params) {
                // TODO Auto-generated method stub


                ArrayList<Contact> contactItemsTemp = new ArrayList<Contact>();

                adapter = new EfficientAdapter(MainActivity.this, contactItems);

                DatabaseHandler db = new DatabaseHandler(MainActivity.this);
                String name = "";
                String id = "";
                String phoneNumber = "";
                // Cursor cursor = null;

                List<Integer> mycontactID;
                mycontactID = db.getAllIDs();

                Iterator value = mycontactID.iterator();

                while (value.hasNext()) {
                    int mg=(Integer)value.next();

                    ContentResolver cr = getContentResolver();
                    Cursor cur = cr.query(ContactsContract.Contacts.CONTENT_URI, null,
                            null, null, null);
                //  Log.d("edw",Integer.toString(mg));
                    if (cur.getCount() > 0) {

                        while (cur.moveToNext()) {
                            id = cur.getString(cur
                                    .getColumnIndex(ContactsContract.Contacts._ID));
                            if (id.equals((mg)))
                                ;
                            {
                                name = cur
                                        .getString(cur
                                                .getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
                                if (Integer
                                        .parseInt(cur.getString(cur
                                                .getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER))) > 0) {

                                    Cursor pCur = cr
                                            .query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
                                                    null,
                                                    ContactsContract.CommonDataKinds.Phone.CONTACT_ID
                                                            + " = ?",
                                                    new String[] { id }, null);
                                    while (pCur.moveToNext()) {
                                        Log.d("number",
                                                pCur.getString(pCur
                                                        .getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER)));
                                        // Do something with phones
                                        phoneNumber = pCur
                                                .getString(pCur
                                                        .getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                                    }
                                    contactItemsTemp.add(new Contact(Integer
                                            .parseInt(id), name, phoneNumber));
                                    pCur.close();

                                    Log.d("Name", name);
                                }
                            }
                        }

                        cur.close();
                    }

                }
                // na kanw to temp contactItems

                List<Integer> messagesx;
                messagesx = db.getAllIDs();
                String namex = "";
                String phonex = "";
                for (Integer mg : messagesx) {
                    for (int i = 0; i < contactItemsTemp.size(); i++) {
                        if (contactItemsTemp.get(i).getID() == mg) {
                            namex = contactItemsTemp.get(i).getContactName();
                            phonex = contactItemsTemp.get(i).getPhoneNumber();
                        }
                    }

                    contactsx.add(new Contact(mg, namex, phonex));
                }

                adapter = new EfficientAdapter(MainActivity.this, contactsx);


                db.close();


                return null;
            }
        }



public static class EfficientAdapter extends ArrayAdapter<Contact>
            implements Filterable {
        private LayoutInflater mInflater;
        // private Bitmap mIcon1;
        private final Context context;
        private final ArrayList<Contact> values;

        public EfficientAdapter(Context context, ArrayList<Contact> values) {
            // Cache the LayoutInflate to avoid asking for a new one each time.
            super(context, R.layout.myobject, values);
            mInflater = LayoutInflater.from(context);
            this.context = context;
            this.values = values;
        }

        /**
         * Make a view to hold each row.
         * 
         * @see android.widget.ListAdapter#getView1(int, android.view.View,
         *      android.view.ViewGroup)
         */
        @Override
        public View getView(final int position, View convertView,
                ViewGroup parent) {

            ViewHolder holder;

            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.myobject, null);

                holder = new ViewHolder();
                holder.contact = (TextView) convertView
                        .findViewById(R.id.contact);
                holder.ph_num = (TextView) convertView
                        .findViewById(R.id.ph_num);

                convertView.setTag(holder);
            }

            else {
                // Get the ViewHolder back to get fast access to the TextView
                // and the ImageView.
                holder = (ViewHolder) convertView.getTag();
            }

            convertView.setOnLongClickListener(new View.OnLongClickListener() {
                private int pos = position;

                @Override
                public boolean onLongClick(View v) {
                    // TODO Auto-generated method stub

                    // prepare the alert box
                    AlertDialog.Builder alertbox = null;
                    alertbox = new AlertDialog.Builder(context);
                    // set the message to display
                    alertbox.setMessage("Are you sure you want to remove the contact from the blacklist?");
                    // add a neutral button to the alert box and assign a click
                    // listener
                    alertbox.setNeutralButton("OK",
                            new DialogInterface.OnClickListener() {

                                @Override
                                public void onClick(DialogInterface dialog,
                                        int which) {
                                    // TODO Auto-generated method stub
                                    Toast.makeText(context,
                                            "Ok button pressed " + pos,
                                            Toast.LENGTH_SHORT).show();

                                    DatabaseHandler db = new DatabaseHandler(
                                            context);
                                    db.deleteContact(values.get(position)
                                            .getID());
                                    db.close();
                                }
                            });

                    alertbox.setNegativeButton("Cancel",
                            new DialogInterface.OnClickListener() {

                                @Override
                                public void onClick(DialogInterface dialog,
                                        int which) {
                                    // TODO Auto-generated method stub
                                    Toast.makeText(context,
                                            "Cancel button pressed " + pos,
                                            Toast.LENGTH_SHORT).show();
                                }
                            });

                    alertbox.show();
                    return true;
                }
            });

            convertView.setOnClickListener(new OnClickListener() {
                private int pos = position;

                @Override
                public void onClick(View v) {
                    // Toast.makeText(context, "Click-" + pos,
                    // Toast.LENGTH_SHORT)
                    // .show();
                }
            });

            holder.contact.setText(getItem(position).getContactName());
            holder.ph_num.setText(getItem(position).getPhoneNumber());

            return convertView;

        }

        static class ViewHolder {
            TextView contact;
            TextView ph_num;

        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return values.size();
        }

        @Override
        public Contact getItem(int position) {
            // TODO Auto-generated method stub
            return values.get(position);
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return 0;
        }

        @Override
        public Filter getFilter() {
            // TODO Auto-generated method stub
            return null;
        }

        public void add(Contact con) {
            values.add(con);

            notifyDataSetChanged();
        }

        public void replace(int index, Contact con) {
            values.set(index, con);
            notifyDataSetChanged();
        }

        public void clear() {
            values.clear();
            notifyDataSetChanged();
        }

        public void remove(Contact con) {
            values.remove(con);
            notifyDataSetChanged();
        }

    }

Answer 1

好吧，我不確定該異常，但似乎您正在嘗試在初始化它之前將聯系人添加到contactx arraylist中。 您將其聲明為實例變量，但是直到doInBackground（）方法結束時才對其進行初始化。 那會拋出空指針...

嘗試把線..

contactx = new ArrayList<Contact>();

在您的onPreExecute（）方法中。

Answer 2

lv = (ListView) findViewById(R.id.blacklist);

我來看看這條線。 您正在嘗試從嵌套類中找到列表視圖。 盡管這將在UI線程上運行，但AsyncTask仍然不是活動。 我相信您的空點是因為您的listview引用為null，因為AsyncTask的實例無法獲取視圖。

Answer 3

1. 為什么在runInBackground內部創建兩次適配器（至今僅使用一次）？ 它應該僅在原始數據被獲取后才在onPostExecute中創建嗎？

2. 您是否可能沒有很好地實現適配器？ 您是否看過Google的“ listView世界”視頻？ 請顯示適配器的代碼。

3. 崩潰有什么例外？