How to add a "Virtual"/"Shadow" Group to SimpleCursorTreeAdapter?

Question

I have a problem concerning a SimpleCursorTreeAdapter which I subclassed in my project. It currently communicates with a SQLite-DB over a ContentProvider. Now, i have the problem that i would like to insert some kind of "Shadow" or "Virtual" Group that is not present in the backend ContentProvider/DB.

I could imagine that this is possible in two ways -- I just can't work out the details. Either we find the actual methods drawing and listing the groups of the SimpleCursorTreeAdapter internally, or we implement a custom Cursor that behaves like a SQliteCursor, except that it returns ColumnCount+1 and appends an "virtual" element for that "virtual" group when queried...

Is there anyone who already did something like this, or might have an idea how to solve this less dirty-hack-y?

Answer 1

... or we implement a custom Cursor that behaves like a SQliteCursor, except that it returns ColumnCount+1 and appends an "virtual" element for that "virtual" group when queried...

Or you implement it at the adapter level, tricking it in thinking the Cursor on which is based has an extra row. I've written an example(a simple scenario) but it needs work:

public class ExtraGroupAdapter extends SimpleCursorTreeAdapter {

    private Cursor mExtraChildCursor;       

    @Override
    protected Cursor getChildrenCursor(Cursor groupCursor) {
        // if groupCursor.getPosition() returns -1 we have to provide the Cursor for our fake group
    }

    @Override
    public int getGroupCount() {
        // 1 more
        return super.getGroupCount() + 1;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded,
            View convertView, ViewGroup parent) {
        if (groupPosition == 0) {
            if (getCursor() == null) {
                throw new IllegalStateException(
                        "this should only be called when the cursor is valid");
            }
            View v;
            if (convertView == null) {
                v = newGroupView(mContext, getCursor(), isExpanded, parent);
            } else {
                v = convertView;
            }
            // if it's position 0 move the group Cursor to position -1 to
            // let the bindGroupView method that is deals with our fake row
            getCursor().moveToPosition(-1);
            bindGroupView(v, mContext, getCursor(), isExpanded);
            return v;
        } else {
            return super.getGroupView(groupPosition - 1, isExpanded,
                    convertView, parent);
        }
    }

    @Override
    protected void bindGroupView(View view, Context context, Cursor cursor,
            boolean isExpanded) {
        if (cursor.getPosition() == -1) {
            // bind our fake row, unfortunately this must be done manually
        } else {
            super.bindGroupView(view, context, cursor, isExpanded);
        }
    }

    @Override
    public View getChildView(int groupPosition, int childPosition,
            boolean isLastChild, View convertView, ViewGroup parent) {
        if (groupPosition == 0) {
            // replicate what the CursorTreeAdapter does for our fake group
            // position 0
            if (getCursor() == null) {
                throw new IllegalStateException(
                        "this should only be called when the cursor is valid");
            }
            View v;
            getCursor().moveToPosition(-1);
            mExtraChildCursor.moveToPosition(childPosition);
            if (convertView == null) {
                v = newChildView(mContext, mExtraChildCursor, isLastChild,
                        parent);
            } else {
                v = convertView;
            }
            bindChildView(v, mContext, mExtraChildCursor, isLastChild);
            return v;
        } else {
            // use the default implementation but offset the Cursor's
            // current position
            return super.getChildView(groupPosition - 1, childPosition,
                    isLastChild, convertView, parent);
        }
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        if (groupPosition == 0) {
            // implement the trick
            if (mExtraChildCursor == null) {
                getCursor().moveToPosition(-1); // in the getChildrenCursor
                                                // a Cursor position of -1
                                                // means it is the fake row
                mExtraChildCursor = getChildrenCursor(getCursor());
                return 0;
            } else {
                return mExtraChildCursor.getCount();
            }
        }
        return super.getChildrenCount(groupPosition);
    }

    @Override
    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {
        if (groupPosition == 0) {
            // hold a reference to the extra Cursor
            mExtraChildCursor = childrenCursor;
            notifyDataSetChanged();
        } else {
            super.setChildrenCursor(groupPosition, childrenCursor);
        }
    }

}

I should have extended CursorTreeAdapter as SimpleCursorTreeAdapter is designed for simple scenarios. What I wrote was for the fake row placed at position 0(but with some careful calculation a different position could be used).