来自其他活动时 ListView 为空

Question

我有一个扩展“SimpleCursorAdapter”的类。

public class MyAdapter extends SimpleCursorAdapter {

private Cursor cursor;
private LayoutInflater inflater;

private int columnIndexRowID;
private int columnIndexFromAddrString;
private int columnIndexToAddrString;

public LastRequestsAdapter(Context context, int layout, Cursor c,
        String[] from, int[] to) {
    super(context, layout, c, from, to);
    this.cursor = c;
    this.inflater = LayoutInflater.from(context);

    this.columnIndexRowID = c.getColumnIndex(MyDBAdapter.KEY_ROWID);
    this.columnIndexFromAddrString = c
            .getColumnIndex(MyDBAdapter.KEY_FROM_ADDR_STRING);
    this.columnIndexToAddrString = c
            .getColumnIndex(MyDBAdapter.KEY_TO_ADDR_STRING);

}
@Override
public View getView(int position, View convertView, ViewGroup parent) {

    ViewHolder viewHolder;

    if(convertView==null){

        convertView = this.inflater.inflate(R.layout.main_activity_last_request_row, null);
        viewHolder = new ViewHolder();
        viewHolder.id = -1;
        viewHolder.fromAddr = (TextView) convertView.findViewById(R.id.from);
        viewHolder.toAddr =(TextView) convertView.findViewById(R.id.to);
        viewHolder.arrow = (ImageView) convertView.findViewById(R.id.last_request_arrow);
        convertView.setTag(viewHolder);
    }else {
        viewHolder = (ViewHolder) convertView.getTag();
    }

    this.cursor.moveToPosition(position);

    viewHolder.id = this.cursor.getInt(columnIndexRowID);
    viewHolder.fromAddr.setText(this.cursor.getString(this.columnIndexFromAddrString));
    viewHolder.toAddr.setText(this.cursor.getString(this.columnIndexToAddrString));
    viewHolder.arrow.setImageResource(R.drawable.arrow_alt);

    return convertView;

}

public class ViewHolder{
    public int id;
    public TextView fromAddr;
    public TextView toAddr;
    public ImageView arrow;
 }
}

它的使用方式如下：

listView.setAdapter(new MyAdapter(this,
            R.layout.main_activity_last_request_row, dbCursor,
            new String[] { MyDBAdapter.KEY_FROM_ADDR_STRING,
                    MyDBAdapter.KEY_TO_ADDR_STRING }, new int[] {
                    R.id.from, R.id.to }));

列表按预期创建。但是：有时此列表中的条目似乎消失了（有时其中一些条目仍然可见）。当我开始一项新活动并（立即）返回到该活动时，例如更改到主屏幕然后返回到我的活动时，似乎每次都会发生这种情况。但是，这种情况只发生一次：当再次切换到“相同的其他”活动然后返回时，所有列表条目仍然可见。 我检查了列表值，似乎它们是从数据库正确接收的，但有些不可见。

有人可以向我解释我做错了什么吗？

Answer 1

getView是类似于Applet中的paint方法的方法，好吧，getCount决定了绘制多少数据，即显示在ListView中

在getCount()中指定List View的大小方法和 getItem{int pos)、getItemId()

public int getCount() {
    return array.length; 

// ForInstance i had an array 
//which contains 5 elements, i want that % elements in List, that's why i had specified the array.length here

}

public Object getItem(int arg0) {
    return arg0;
}

public long getItemId(int arg0) {
    return arg0;
}