I have created a dynamic ListView where objects are added from top.
When the user press a button the listView is updated from the contents of an array, then notifyDataSetChanged() is called on the custom arrayAdapter.
Now I want to mantain the list position when adding, so I added this code:
// pausedCounter trace the number of objects(lines) to add to the listView
int idx = listView.getFirstVisiblePosition() + pausedCounter;
View first = listView.getChildAt(0);
int position = 0;
if (first != null)
position = first.getTop();
// cycle to add the new objects to the listView
for (Tweet[] tweets1 : pausedTweets)
super.updateTweets(tweets1);
listView.setSelectionFromTop(idx, position);
// reset of counter and accumulator
pausedTweets = new ArrayList<Tweet[]>();
pausedCounter = 0;
This code behave in this way: if the getFirstVisiblePosition returns 2, and the pausedCounter is 5, after the update the list will be set to the 3th of the new five elements.
What I want is to have the first visible element of the list set to the 8th.
After further tests I found out that the number of childrens of the listView doesn't change during the run of this piece of code, so it updates the size of the listView after I called setSelectionFromTop. Could be this the problem?
The trick was this:
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelectionFromTop(idx, finalPosition);
}
});
Using the post method permits to wait the update of the ListView before change position.
Related
I want to implement search functionality for my RecyclerView. On text changed i want to change the data that are displayed with this widget. Maybe this question has been asked before or is simple, but I don't know how the change the data that is to be shown...
My RecyclerView is defined as follows:
// 1. get a reference to recyclerView
mRecyclerView = (RecyclerView)findViewById(R.id.recyclerView);
// 2. set layoutManger
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
// 3. create an adapter
mAdapter = new ItemsAdapter(itemsData);
// 4. set adapter
mRecyclerView.setAdapter(mAdapter);
And the data that I am showing is something like:
ItemData itemsData[] = { new ItemData("Mary Richards"),
new ItemData("Tom Brown"),
new ItemData("Lucy London")
};
So when when I want to give the adapter another set of data, another array (with one item for example), what should I do?
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).
A better approach would be finding which items are removed and calling notifyItemRemoved(index). Don't forget to actually remove the item. This will let RecyclerView run predictive animations. Assuming you have an Adapter that internally uses an ArrayList, implementation would look like this:
// adapter code
final List<ItemData> mItems = new ArrayList(); //contains your items
public void filterOut(String filter) {
final int size = mItems.size();
for(int i = size - 1; i>= 0; i--) {
if (mItems.get(i).test(filter) == false) {
mItems.remove(i);
notifyItemRemoved(i);
}
}
}
It would perform even better if you can batch notifyItemRemoved calls and use notifyItemRangeRemoved instead. It would look sth like: (not tested)
public void filterOut(String filter) {
final int size = mItems.size();
int batchCount = 0; // continuous # of items that are being removed
for(int i = size - 1; i>= 0; i--) {
if (mItems.get(i).test(filter) == false) {
mItems.remove(i);
batchCount ++;
} else if (batchCount != 0) { // dispatch batch
notifyItemRangeRemoved(i + 1, batchCount);
batchCount = 0;
}
}
// notify for remaining
if (batchCount != 0) { // dispatch remaining
notifyItemRangeRemoved(0, batchCount);
}
}
You need to extend this code to add items that were previously filtered out but now should be visible (e.g. user deletes the filter query) but I think this one should give the basic idea.
Keep in mind that, each notify item call affects the ones after it (which is why I'm traversing the list from end to avoid it). Traversing from end also helps ArrayList's remove method performance (less items to shift).
For example, if you were traversing the list from the beginning and remove the first two items.
You should either call
notifyItemRangeRemoved(0, 2); // 2 items starting from index 0
or if you dispatch them one by one
notifyItemRemoved(0);
notifyItemRemoved(0);//because after the previous one is removed, this item is at position 0
This is my answer - thanks to Ivan Skoric from his site: http://blog.lovelyhq.com/creating-lists-with-recyclerview-in-android/
I created an extra method inside my adapter class:
public void updateList(List<Data> data) {
mData = data;
notifyDataSetChanged();
}
Then each time your data changes, you just call this method passing in your new data and your view should change to reflect it.
Just re-initialize your adapter:
mAdapter = new ItemsAdapter(newItemsData);
or if you only need to remove add a few specific items rather than a whole list:
mAdapter.notifyItemInserted(position);
or
mAdapter.notifyItemRemoved(position);
If you want to change the complete Adapter in the recycler view. you can just simply set by recycler.setAdapter(myAdapter);
It will automatically remove the old adapter from recycler view and replace it with your new adapter.
As ygit answered, swapAdapter is interesting when you have to change the whole content.
But, in my FlexibleAdapter, you can update the items with updateDataSet. You can even configure the adapter to call notifyDataSetChanged or having synchronization animations (enabled by default). That, because notifyDataSetChanged kills all the animations, but it's good to have for big lists.
Please have a look at the description, demoApp and Wiki pages: https://github.com/davideas/FlexibleAdapter
I'm using a ListView with a custom ArrayAdapter.
The List is an infinite scroll of tweets.
Updates to the list are inserted from the top.
I want to obtain an effect as the Twitter application. I'm not talking about the "scroll to update", but to maintain the position after the update.
I've just implemented some code that works in that way. Here it is:
// get the position of the first visible tweet.
// pausedCounter traces the number of tweets in the waiting line
final int idx = listView.getFirstVisiblePosition() + pausedCounter;
View first = listView.getChildAt(0);
int position = 0;
if (first != null)
position = first.getTop();
// here I update the listView with the new elements
for (Tweet[] tweets1 : pausedTweets)
super.updateTweets(tweets1);
final int finalPosition = position;
// this code maintain the position
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelectionFromTop(idx, finalPosition);
}
});
The problem of this code is that for an instant the listView goes to the first element of the list, then kick in the setSelectionFromTop and it goes to the correct position.
This sort of "flickering" is annoying, and I want to remove it.
I found out only this solution:
// add the new elements to the current ArrayAdapter
for (Tweet[] tweets1 : pausedTweets)
super.updateTweets(tweets1);
// create a NEW ArrayAdapter using the data of the current used ArrayAdapter
// (this is a custom constructor, creates an ArrayAdapter using the data from the passed)
TweetArrayAdapter newTweetArrayAdapter =
new TweetArrayAdapter(context, R.layout.tweet_linearlayout, (TweetArrayAdapter)listView.getAdapter());
// change the ArrayAdapter of the listView with the NEW ArrayAdapter
listView.setAdapter(newTweetArrayAdapter);
// set the position. Remember to add as offset the number of new elements inserted
listView.setSelectionFromTop(idx, position);
In this way I have no "flickering" at all!
I set a timer in my app, I could get some information from a web service and resulted in a list view to display. Now my problem is that every time the timer runs, scroll back to the beginning ...
how can i keep Scroll position with every refresh in list view ?
part of my code:
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(DashboardActivity.this,
all_chat,
R.layout.list_item,
new String[] { TAG_FULLNAME,
TAG_DATE,
TAG_MESSAGE },
new int[] { R.id.fullname,
R.id.date,
R.id.message }
);
// updating listview
setListAdapter(adapter);
}
});
TNx.
Do not call setAdapter(). Do something like this:
ListAdapter adapter; // declare as class level variable
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
*/
if (adapter == null) {
adapter = new SimpleAdapter(
DashboardActivity.this, all_chat, R.layout.list_item, new String[]{TAG_FULLNAME, TAG_DATE, TAG_MESSAGE},
new int[]{R.id.fullname, R.id.date, R.id.message});
setListAdapter(adapter);
} else {
//update only dataset
allChat = latestetParedJson;
((SimpleAdapter) adapter).notifyDataSetChanged();
}
// updating listview
}
});
You can add the following attribute to your ListView in xml.
android:stackFromBottom="true"
android:transcriptMode="alwaysScroll"
Add these attributes and your ListView will always be drawn at bottom like you want it to be in a chat.
or if you want to keep it at the same place it was before, replace alwaysScroll to normal
in the android:transcriptMode attribute.
Cheers!!!
I had the same issue, tried a lot of things to prevent the list from changing its scroll position, including:
android:stackFromBottom="true"
android:transcriptMode="alwaysScroll"
and not calling listView.setAdapter();
None of it worked until I found this answer:
Which looks like this:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
// ...
// restore index and position
mList.setSelectionFromTop(index, top);
Explanation:
ListView.getFirstVisiblePosition() returns the top visible list item. But this item may be partially scrolled out of view, and if you want to restore the exact scroll position of the list you need to get this offset. So ListView.getChildAt(0) returns the View for the top list item, and then View.getTop() - mList.getPaddingTop() returns its relative offset from the top of the ListView. Then, to restore the ListView's scroll position, we call ListView.setSelectionFromTop() with the index of the item we want and an offset to position its top edge from the top of the ListView.
There's a good article by Chris Banes. For the first part, just use ListView#setSelectionFromTop(int) to keep the ListView at the same visible position. To keep the ListView from flickering, the solution is to simply block the ListView from laying out it's children.
I am using PullToRefresh in my android app. It is working fine so far.
Issue I am facing is when I download new x rows on "Release to refresh" from TOP new rows pushes existing rows and starts from 0 position it is annoying for the user. What I want is, after downloading new set of rows list should remain there and let user fling down to view new set of rows.
any idea how can I achieve this?
This is what i use
//Get old position before updating adapter
final int old_pos = mListView.getRefreshableView().getFirstVisiblePosition()+1;
//Set Adapter
mListView.setAdapter(mListAdapter);
//Set the list to old postion
//mListView.getRefreshableView().setSelection(old_pos);
mListAdapter.notifyDataSetChanged();
mListView.onRefreshComplete();
mListView.post(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
mListView.getRefreshableView().setSelection(old_pos);
}
});
also check this:
Maintain/Save/Restore scroll position when returning to a ListView
I have a listView that contains lots of elements i.e. we have to scroll down to see all the elements. Now what i want to do is, click all the listView elements. How can I do that. Right now,I am using the following code but it doesn't scroll automatically. Please help.
ListView l = solo.getCurrentListViews().get(0);
assertNotNull("No list views!", l);
assertTrue("No items in list view!", l.getChildCount() > 0);
// Get the last list item
View v = l.getChildAt(l.getChildCount());
System.out.println("getChildCount: " + l.getChildCount());
int i = 1;
while (i <= l.getChildCount()) {
solo.clickInList(i);
solo.goBack();
i++;
}
I have previously used these helper functions in a slightly different state to handle most of what we need with listviews:
public View getViewAtIndex(final ListView listElement, final int indexInList, Instrumentation instrumentation) {
ListView parent = listElement;
if (parent != null) {
if (indexInList <= parent.getAdapter().getCount()) {
scrollListTo(parent, indexInList, instrumentation);
int indexToUse = indexInList - parent.getFirstVisiblePosition();
return parent.getChildAt(indexToUse);
}
}
return null;
}
public <T extends AbsListView> void scrollListTo(final T listView,
final int index, Instrumentation instrumentation) {
instrumentation.runOnMainSync(new Runnable() {
#Override
public void run() {
listView.setSelection(index);
}
});
instrumentation.waitForIdleSync();
}
With these your method would be:
ListView list = solo.getCurrentListViews().get(0);
for(int i=0; i < list.getAdapter().getCount(); i++){
solo.clickOnView(getViewAtIndex(list, i, getInstrumentation()))
}
It looks like your code, as currently implemented, is only considering the visibile list items when controlling the loop and handling the clicking. It's important to note the behavior of two things:
First, there's a concept called view recycling in Android that helps conserve memory when dealing with ListViews. Only the views that are currently on screen are created, and once they scroll off the screen they'll be repopulated with new data. Therefore, calling methods like getChildCount and getChildAt on a ListView will only perform these operations on the visible items. To find information about the data that populates the list, you can call methods such as getCount() or getItem() on the ListView's adapter.
Second, the clickInList() method is 1-indexed, relative to the current position of the list, and can only be used for visible items. As far as I know, it will never scroll your list automatically. This means that calling clickInList(2) when at the top of the list will click the second item, but then calling clickInList(2) again when the 30th item is at the top of the list will click the 32nd.
Knowing these two things, your solution will need to consider all of the list data and perhaps have a bit more precision when making clicks. Here's how I'd rewrite your while loop to ensure you'll be able to handle every item on the list, hope this helps:
ListAdapter adapter = l.getAdapter();
for(int i=0; i < adapter.getCount(); i++)
{
//Scroll down the list to make sure the current item is visible
solo.scrollListToLine(l, i);
//Here you need to figure out which view to click on.
//Perhaps using adapter.getItem() to get the data for the current list item, so you know the text it is displaying.
//Here you need to click the item!
//Even though you're in a list view, you can use methods such as clickOnText(), which might be easier based on how your adapter is set up
solo.goBack();
}
It should help you(not tested):
public void clickAllElementsOnListView(int index) {
ListView listView = solo.getCurrentListViews().get(index);
count = listView.getAdapter() != null ? listView.getAdapter().getCount() : 0;
for (int i = 0; i < count; i++) {
scrollListToLine(listView, i);
solo.clickInList(1, index);
solo.goBack();
}
}
protected void scrollListToLine(final ListView listView, final int line) {
getInstrumentation().runOnMainSync(new Runnable() {
public void run() {
listView.setSelection(line);
}
});
}