直到今天，我对自定义 CursorAdapter 上的代码一直不满意，直到今天我决定审查它并修复一个困扰我很长时间的小问题（有趣的是，我的应用程序的用户都没有报告过这样的问题）。
这是我的问题的一个小描述：
我的自定义 CursorAdapter 覆盖newView()，bindView()而不是getView()我看到的大多数示例。我在这两种方法之间使用 ViewHolder 模式。但我的主要问题是我为每个列表项使用的自定义布局，它包含一个ToggleButton.
问题是当列表项视图滚动出视图然后滚动回视图时，按钮状态没有保持。之所以存在这个问题，是因为它cursor从来没有意识到在ToggleButton按下 时数据库数据发生了变化，并且它总是在提取相同的数据。单击时我尝试重新查询光标ToggleButton并解决了问题，但是速度很慢。
我已经解决了这个问题，我在这里发布了整个课程以供审查。我已经针对这个特定问题彻底评论了代码，以更好地解释我的编码决定。
你觉得这段代码好看吗？你会以某种方式改进/优化或改变它吗？
PS：我知道 CursorLoader 是一个明显的改进，但我暂时没有时间处理这么大的代码重写。这是我在路线图中的东西。
这是代码：
public class NotesListAdapter extends CursorAdapter implements OnClickListener {
private static class ViewHolder {
ImageView icon;
TextView title;
TextView description;
ToggleButton visibility;
}
private static class NoteData {
long id;
int iconId;
String title;
String description;
int position;
}
private LayoutInflater mInflater;
private NotificationHelper mNotificationHelper;
private AgendaNotesAdapter mAgendaAdapter;
/*
* This is used to store the state of the toggle buttons for each item in the list
*/
private List<Boolean> mToggleState;
private int mColumnRowId;
private int mColumnTitle;
private int mColumnDescription;
private int mColumnIconName;
private int mColumnVisibility;
public NotesListAdapter(Context context, Cursor cursor, NotificationHelper helper, AgendaNotesAdapter adapter) {
super(context, cursor);
mInflater = LayoutInflater.from(context);
/*
* Helper class to post notifications to the status bar and database adapter class to update
* the database data when the user presses the toggle button in any of items in the list
*/
mNotificationHelper = helper;
mAgendaAdapter = adapter;
/*
* There's no need to keep getting the column indexes every time in bindView() (as I see in
* a few examples) so I do it once and save the indexes in instance variables
*/
findColumnIndexes(cursor);
/*
* Populate the toggle button states for each item in the list with the corresponding value
* from each record in the database, but isn't this a slow operation?
*/
for(mToggleState = new ArrayList<Boolean>(); !cursor.isAfterLast(); cursor.moveToNext()) {
mToggleState.add(cursor.getInt(mColumnVisibility) != 0);
}
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
View view = mInflater.inflate(R.layout.list_item_note, null);
/*
* The ViewHolder pattern is here only used to prevent calling findViewById() all the time
* in bindView(), we only need to find all the views once
*/
ViewHolder viewHolder = new ViewHolder();
viewHolder.icon = (ImageView)view.findViewById(R.id.imageview_icon);
viewHolder.title = (TextView)view.findViewById(R.id.textview_title);
viewHolder.description = (TextView)view.findViewById(R.id.textview_description);
viewHolder.visibility = (ToggleButton)view.findViewById(R.id.togglebutton_visibility);
/*
* I also use newView() to set the toggle button click listener for each item in the list
*/
viewHolder.visibility.setOnClickListener(this);
view.setTag(viewHolder);
return view;
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
Resources resources = context.getResources();
int iconId = resources.getIdentifier(cursor.getString(mColumnIconName),
"drawable", context.getPackageName());
String title = cursor.getString(mColumnTitle);
String description = cursor.getString(mColumnDescription);
/*
* This is similar to the ViewHolder pattern and it's need to access the note data when the
* onClick() method is fired
*/
NoteData noteData = new NoteData();
/*
* This data is needed to post a notification when the onClick() method is fired
*/
noteData.id = cursor.getLong(mColumnRowId);
noteData.iconId = iconId;
noteData.title = title;
noteData.description = description;
/*
* This data is needed to update mToggleState[POS] when the onClick() method is fired
*/
noteData.position = cursor.getPosition();
/*
* Get our ViewHolder with all the view IDs found in newView()
*/
ViewHolder viewHolder = (ViewHolder)view.getTag();
/*
* The Html.fromHtml is needed but the code relevant to that was stripped
*/
viewHolder.icon.setImageResource(iconId);
viewHolder.title.setText(Html.fromHtml(title));
viewHolder.description.setText(Html.fromHtml(description));
/*
* Set the toggle button state for this list item from the value in mToggleState[POS]
* instead of getting it from the database with 'cursor.getInt(mColumnVisibility) != 0'
* otherwise the state will be incorrect if it was changed between the item view scrolling
* out of view and scrolling back into view
*/
viewHolder.visibility.setChecked(mToggleState.get(noteData.position));
/*
* Again, save the note data to be accessed when onClick() gets fired
*/
viewHolder.visibility.setTag(noteData);
}
@Override
public void onClick(View view) {
/*
* Get the new state directly from the toggle button state
*/
boolean visibility = ((ToggleButton)view).isChecked();
/*
* Get all our note data needed to post (or remove) a notification
*/
NoteData noteData = (NoteData)view.getTag();
/*
* The toggle button state changed, update mToggleState[POS] to reflect that new change
*/
mToggleState.set(noteData.position, visibility);
/*
* Post the notification or remove it from the status bar depending on toggle button state
*/
if(visibility) {
mNotificationHelper.postNotification(
noteData.id, noteData.iconId, noteData.title, noteData.description);
} else {
mNotificationHelper.cancelNotification(noteData.id);
}
/*
* Update the database note item with the new toggle button state, without the need to
* requery the cursor (which is slow, I've tested it) to reflect the new toggle button state
* in the list because the value was saved in mToggleState[POS] a few lines above
*/
mAgendaAdapter.updateNote(noteData.id, null, null, null, null, visibility);
}
private void findColumnIndexes(Cursor cursor) {
mColumnRowId = cursor.getColumnIndex(AgendaNotesAdapter.KEY_ROW_ID);
mColumnTitle = cursor.getColumnIndex(AgendaNotesAdapter.KEY_TITLE);
mColumnDescription = cursor.getColumnIndex(AgendaNotesAdapter.KEY_DESCRIPTION);
mColumnIconName = cursor.getColumnIndex(AgendaNotesAdapter.KEY_ICON_NAME);
mColumnVisibility = cursor.getColumnIndex(AgendaNotesAdapter.KEY_VISIBILITY);
}
}