Develop Reference

Force resort of Android appcompat `SortedList`?

I have a SortedList being displayed in a RecyclerView by my RecyclerView.Adapter.
I use 2 custom Comparator instances from withing the SortedListAdapterCallback.compare() method to either sort A-Z or Z-A.
static class A2Z implements Comparator<Item> {
#Override
public int compare(Item t0, Item t1) {
return t0.mText.compareTo(t1.mText);
}
}
static class Z2A extends A2Z {
#Override
public int compare(Item t0, Item t1) {
return -1 * super.compare(t0, t1);
}
}
Item simply contains a single String mText;
I use my comparators in the SortedListAdapterCallback.compare() method:
private Comparator<Item> a2z = new A2Z();
private Comparator<Item> z2a = new Z2A();
private Comparator<Item> comparator = z2a;
#Override
public int compare(Item t0, Item t1) {
return comparator.compare(t0, t1);
}
I change the comparators on a button press. The list on screen does not update.
After logging values in the various methods, I can tell that the list itself is not updating. Notifying the adapter of changes simply redraws the old list, without resorting it.
So how do I force the underlying SortedList to resort all the items?
Perhaps it is best to just create a new Adapter each time, as in this question:
RecyclerView change data set

SortedList does not have functionality to resort itself - each instance only has a single sort order.
Went with creating a new adapter for each resort, as per Yigit's answer to the above referenced question:
If you have stable ids in your adapter, you can get pretty good
results (animations) if you create a new array containing the filtered
items and call
recyclerView.swapAdapter(newAdapter, false);
Using swapAdapter hints RecyclerView that it can re-use view holders.
(vs in setAdapter, it has to recycle all views and re-create because
it does not know that the new adapter has the same ViewHolder set with
the old adapter).

Use a switch statement inside the compare method with a local control flag (an enum is a good idea).
After changing the switch flag, call sortedList.replaceAll.
#Override
public int compare(PmpRole pmpRoleA, PmpRole pmpRoleB) {
switch (mSorter){
case IDX:
return pmpRoleA.getIdx().compareTo(pmpRoleB.getIdx());
case TITLE:
return pmpRoleA.getTitleIdx().compareTo(pmpRoleB.getTitleIdx());
case ID_IDX:
return pmpRoleA.getIdIdx().compareTo(pmpRoleB.getIdIdx());
}
return -1;
}
public void setSorter(Sorter sorter){
mSorter = sorter;
mPmpRoleSortedList.replaceAll(mPmpRoles);
}
Maintains animation functionality etc.

How to apply setItemChecked(position,true) with RecyclerView in Android?

I am developing a Material Design Navigation Drawer. I've created a new class RecyclerItemClickListener implements RecyclerView.OnItemTouchListener in it to handle the user's click on the list items. I use the class this way within the MainActivity class' onCreate method:
mRecyclerView.addOnItemTouchListener(
new RecyclerItemClickListener(this, mRecyclerView, new RecyclerItemClickListener.OnItemClickListener() {
#Override
public void onItemClick(View view, int position) {// do whatever
if(position!=0){
setItemChecked(position, true);
setSelectable(true);
boolean isSelected = view.isSelected();
view.setActivated(isSelected);
selectItem(position);
}
}
#Override
public void onItemLongClick(View view, int position){
// ...
}
})
);
I based this code from this blog post: RecyclerView part 2 but it's not getting the job done, and to me it's not clear at all on how am I supposed to get it working.
I've also checked out this seemingly easy solution: Innodroid - Tracking Selected Item in RecyclerView (also quoted in this answer) but it's not clear on how I am supposed to derive my MyAdapter class to the TrackSelectionAdapter class.
What's the best way to highlight list items? I'm stuck.
Please help.

I think, I've found the best tutorial on how to use the RecyclerView with all functions we need and with no libraries (single+multiselection, hightlight, ripple, click and remove in multiselection, etc...). From a first look it seems well explained.
Here it is --> http://enoent.fr/blog/2015/01/18/recyclerview-basics/
[EDIT] I finally found the time to try it out and I even created my own more flexible, everybody can benefit my improvements: https://github.com/davideas/FlexibleAdapter.
In this link I also explain how it works. Please have a look and feel free to add it to your project.

ListView: grouping items by section

Taking for example Gmail App, on my Navigation Drawer, I want a ListView that is grouped by section, similar to inbox, all labels.
Is this behavior achieved by using multiple ListView separated by a "header" TextView (which I have to build manually obviously), or is this section-grouped behavior supported by the Adapter or ListView?

Don't use multiple ListViews, it will mess things up for the scroll.
What you describe can be achieve by using only one ListView + adapter with multiple item view types like this:
public class MyAdapter extends ArrayAdapter<Object> {
// It's very important that the first item have a value of 0.
// If not, the adapter won't work properly (I didn't figure out why yet)
private int TYPE_SEPARATOR = 0;
private int TYPE_DATA = 1;
class Separator {
String title;
}
public MyAdapter(Context context, int resource) {
super(context, resource);
}
#Override
public boolean areAllItemsEnabled() {
return false;
}
#Override
public int getItemViewType(int position) {
if (getItem(position).getClass().isAssignableFrom(Separator.class)) {
return TYPE_SEPARATOR;
}
return TYPE_DATA;
}
#Override
public int getViewTypeCount() {
// Assuming you have only 2 view types
return 2;
}
#Override
public boolean isEnabled(int position) {
// Mark separators as not enabled. That way, the onclick and onlongclik listener
// won't be triggered for those items.
return getItemViewType(position) != TYPE_SEPARATOR;
}
}
You just have to implement your own getView method for a correct rendering.

I am not sure exactly how the Gmail app achieves this behavior, but it seems as though you should work on a custom adapter. Using multiple list views would not be a productive way to approach this problem, as one wants to keep the rows of data (messages) together in single list items.

Re-index/Refresh a SectionIndexer

Is there any way to re-index a SectionIndexer after new items are added to a ListView?
I found this solution, but the overlay is position in the top left corner after the SectionIndexer is refreshed.
Anyone have any ideas?

Once the FastScroller (its in AbsListView class that ListView extends from) obtains your sections by calling SectionIndexer#getSections(), it never re-obtains them unless you enable/disable fast-scrolling like mentioned in the link you mentioned. To get the value to be displayed on screen, FastScroller calls the section's toString method.
One potential solution is to have a custom SectionIndexer that have the following characteristics:
The sections array is of fixed length (max length of the expected number of sections. For example, if the sections represent English alphabet it will be 26)
Have a custom object to represent sections, rather than using strings
Overwrite the toString method of your custom section object to display what you want based on the current 'section values'.
-
e.g. In your custom SectionIndexer
private int mLastPosition;
public int getPositionForSection(int sectionIndex) {
if (sectionIndex < 0) sectionIndex = 0;
// myCurrentSectionLength is the number of sections you want to have after
// re-indexing the items in your ListView
// NOTE: myCurrentSectionLength must be less than getSections().length
if (sectionIndex >= myCurrentSectionLength) sectionIndex = myCurrentSectionLength - 1;
int position = 0;
// --- your logic to find the position goes in here
// --- e.g. see the AlphabeticIndexer source in Android repo for an example
mLastPosition = position;
return mLastPosition;
}
public Object[] getSections() {
// Assume you only have at most 3 section for this example
return new MySection[]{new MySection(), new MySection(), new MySection()};
}
// inner class within your CustomSectionIndexer
public class MySection {
MySection() {}
public String toString() {
// Get the value to displayed based on mLastPosition and the list item within that position
return "some value";
}
}

I found that the best way to do this is to call setContentView(R.layout.whatever) and then re-populate the ListView with your new adapter / new data items. This will redraw the ListView with your new items and the FastScroll Overlay will appear in the correct place.

I found notifyDataSetInvalidated working fine, here's the idea:
public class MyAdapter extends XXXAdapter implements SectionIndexer {
...
public void updateDataAndIndex(List data, Map index) {
// update sections
// update date set
notifyDataSetInvalidated();
}
}
update your data set and index (sections) somehow, and then notifyDataSetInvalidated, the index will refresh.

You can force reloading sections list to ListView by listView.setAdapter(yourAdapter)

android fastScroll only covers part of the list

I have a class which implements expandable list activity.
In the XML code (or I can do it in java), I set fastScrollEnabled to true. This does in deed enable fast scroll. BUT fast scroll only works in the top portion of the list. Like I can use the fastscroll thumb bar to scroll the whole list but only works in the top section of the scroll bar. It's not proportionate to the entire list. I can drag the thumb bar to the bottom of the list but it does no scrolling since the listview is already scrolled to the bottom due to the odd behaviour of it only working in the top portion of the list.
Confusing I know, I can try to clarify more if needed....
I do implement a custom BaseExpandableListAdapter.

I've just found a workaround to prevent the system to display this wrong behaviour.
There are two scenarios which use different code for the SectionIndexer to work.
The first scenario is the case that you use the FastScrollbar-Thumb to navigate to the next section. Assuming that the groups are your sections the overriden methods for implementing the SectionIndexer would look like that:
#Override
public int getPositionForSection(int section) {
return section;
}
// Gets called when scrolling the list manually
#Override
public int getSectionForPosition(int position) {
return ExpandableListView.getPackedPositionGroup(
expandableListView
.getExpandableListPosition(position));
}
The second scenario is the case that you scroll the list manually and the fast scrollbars move according to the sections, not to all items. The code therefore looks like that:
#Override
public int getPositionForSection(int section) {
return expandableListView.getFlatListPosition(
ExpandableListView.getPackedPositionForGroup(section));
}
// Gets called when scrolling the list manually
#Override
public int getSectionForPosition(int position) {
return ExpandableListView.getPackedPositionGroup(
expandableListView
.getExpandableListPosition(position));
}
As one can see these two behaviours can not play together without further adoption.
The workaround to make it both work is to catch the case when someone is scrolling per hand (i.e. scrolling via touch). This can be done with implementing the OnScrollListener interface with the adapter class and set it onto the ExpandableListView:
public class MyExpandableListAdapter extends BaseExpandableListAdapter
implements SectionIndexer, AbsListView.OnScrollListener {
// Your fields here
// ...
private final ExpandableListView expandableListView;
private boolean manualScroll;
public MyExpandableListAdapter(ExpandableListView expandableListView
/* Your other arguments */) {
this.expandableListView = expandableListView;
this.expandableListView.setOnScrollListener(this);
// Other initializations
}
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
this.manualScroll = scrollState == SCROLL_STATE_TOUCH_SCROLL;
}
#Override
public void onScroll(AbsListView view,
int firstVisibleItem,
int visibleItemCount,
int totalItemCount) {}
#Override
public int getPositionForSection(int section) {
if (manualScroll) {
return section;
} else {
return expandableListView.getFlatListPosition(
ExpandableListView.getPackedPositionForGroup(section));
}
}
// Gets called when scrolling the list manually
#Override
public int getSectionForPosition(int position) {
return ExpandableListView.getPackedPositionGroup(
expandableListView
.getExpandableListPosition(position));
}
// Your other methods
// ...
}
That fixed the bug for me.

This is a bug in the fast scroller. It does not play well with ExpandableListView.
See my code.
(it also includes a work-around for some cases)