Android BaseAdapter : position not really the position?

Question

当我使用 BaseAdapter 的 ListView 离开屏幕时，每一行不再保持连续的位置。除了这个我不知道还能怎么解释。

如果我的 BA/LV 在屏幕上显示 4 个项目，并且我添加了一个显示每一行的 TextView 的 View ，它会显示 0、1、2、3 作为行号(这是正确的)。但是，一旦我将列表向下滚动到底部的 4 项(第 5-8 项)，它就会显示为 4、5、0、1？为什么？

编辑:我确实发现如果我改变

rv = (RowView)convertView;

到

rv =  new RowView(mContext,(cursor.getString(2)),
                        (cursor.getString(5)),
                        cursor.getString(cursor.getColumnIndex(DBHelper.KEY_IMAGEFILENAME)),
                        cursor.getString(cursor.getColumnIndex(DBHelper.KEY_CITY)),position);

它可以工作，但它不会重复使用代码。所以，我想我走在正确的轨道上。我确实尝试了一些方便的方法，但这对我没有太大帮助，因为我需要在构造函数启动之前设置这些值。我是否需要创建一个新方法并在最后触发它？比如addRow方法？这也会导致它滚动得非常慢。

          @Override
               public void onCreate(Bundle bundle)
               {
                 super.onCreate(bundle);
                 //setContentView(R.layout.findlist);
                 //getListView().setEmptyView(findViewById(R.id.empty));
                 mDbHelper = new DBHelper(this);
                 mDbHelper.open();
                 cursor = mDbHelper.fetchAllLocations();
                 startManagingCursor(cursor);
                 mAdapter = new myListAdapter(this);
                 setListAdapter(mAdapter);
        
               }
    public class myListAdapter extends BaseAdapter {
            public String testing;
            public myListAdapter(Context c) {
                mContext = c;
                // TODO Auto-generated constructor stub
            }
    
            @Override
            public int getCount() {
                // TODO Auto-generated method stub
                return cursor.getCount();
            }
    
            @Override
            public Object getItem(int position) {
                // TODO Auto-generated method stub
                return position;
            }
    
            @Override
            public long getItemId(int position) {
                // TODO Auto-generated method stub
                return position;
            }
    
            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
    
                
                 cursor.moveToPosition(position);
                 RowView rv;
    
    
                 if (convertView == null) {
                        rv = new RowView(mContext,(cursor.getString(2)),
                                (cursor.getString(5)),
                                cursor.getString(cursor.getColumnIndex(DBHelper.KEY_IMAGEFILENAME)),
                                cursor.getString(cursor.getColumnIndex(DBHelper.KEY_CITY)),position);
                    } else {
                        rv = (RowView) convertView;
                        try {
              // I KNOW THIS SECTION IS NOT RIGHT, BUT I HAVE BEEN MESSING IN HERE          
                        rv.setAddress(cursor.getString(2));
                        rv.setCity(cursor.getString(5));
                        rv.setFocusable(true);
                        rv.setClickable(true); }
                        catch (Exception e) {
                            rv = (RowView) convertView;
                            rv.setAddress(cursor.getString(2));
                            rv.setCity(cursor.getString(5));
                            rv.setFocusable(true);
                            rv.setClickable(true); 
                            Toast mToast;
                            mToast = Toast.makeText(FindList.this, "Error :" + e.toString() ,
                                    Toast.LENGTH_LONG);
                            mToast.show();
                        }
                    }
                    
                 return rv;
            }
            
            public void addItems() {
    
                 //String[] from = new String[] { DBHelper.KEY_BUSINESSNAME, DBHelper.KEY_ADDRESS, DBHelper.KEY_CITY, DBHelper.KEY_GPSLONG, DBHelper.KEY_GPSLAT,  DBHelper.KEY_IMAGEFILENAME  + ""};
                 // create array of values of widgits
                 //to = new int[] { R.id.businessname, R.id.address, R.id.city, R.id.gpslong, R.id.gpslat, R.id.preview};
                 // Now create an array adapter and set it to display using our row from notes_row.xml
                 
                 
            }
            
            
            
        }


private class RowView extends LinearLayout {
        private TextView mAddress;
        private TextView mCity;
        public ImageView mArrow;
        public ImageView mPicture;
        public String mPathName;
        public String mDateTime;
        public RowView(Context context, String title, String words, String pathName, String city, int position) {
            super(context);

            this.setOrientation(HORIZONTAL);
            this.setVerticalGravity(16); //CENTER_VERTICAL 

            // Here we build the child views in code. They could also have
            // been specified in an XML file.
           
            //DISPLAY DELETE BUTTON
            Button mButton = new Button(context);
            mButton.setFocusable(false);
            mButton.setId(position);
            mButton.setBackgroundResource(R.drawable.delete3);
            addView(mButton, new LinearLayout.LayoutParams(
                    LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
            
            TextView mTitle;
            mTitle = new TextView(context);
            mTitle.setText(Integer.toString(position));
            addView(mTitle, new LinearLayout.LayoutParams(
                    LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));

            this.setOrientation(HORIZONTAL);      
            
            try {
             Bitmap bm = Bitmap.createScaledBitmap(BitmapFactory.decodeFile(cursor.getString(cursor.getColumnIndex(DBHelper.KEY_IMAGEFILENAME))),100, 100, true);
                mPicture = new ImageView(context);
                mPicture.setImageBitmap(bm);    
           } catch (Exception e) { 
                 mPicture = new ImageView(context);
                 mPicture.setImageResource(R.drawable.noimage);
           }     
            
            addView(mPicture, new LinearLayout.LayoutParams(
                    LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
            
            mArrow = new ImageView(context);
            mArrow.setBackgroundResource(R.drawable.arrowleft3);
            addView(mArrow, new LinearLayout.LayoutParams(
                    LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
          
            currentPosition = position;
            Button button = (Button)findViewById(position);
            button.setOnClickListener(mCorkyListener);
            
        }

Answer 1

当使用 convertView 时，您会得到一个以前使用过但不再显示的 View 。您应该注意用当前项目的值重置其所有属性。否则，您在 RowView 构造函数中设置的所有值将与您第一次创建该 View 时赋予它的值保持一致。

为了更好地理解 ListViews，您必须了解它只使用一组有限的 RowViews，只是足以填充显示的数量，还有一些将在必须显示它们之前填充您的数据。