I'm working on a ListView based app and I have a very weird problem, my ListItems are reappering and the correct item is not shown in the correct spot. For the sake of making this easy to understand I've set the text on each ListItem to be the same as it's position. I'm doing this in my adapters getView() call. If I have my Nexus 7 4 ListItems are visible. If I have a total of 10 ListItems then it will go like 0, 1, 3, 4, 0, 1, 2, 3, 4. This goes for all devices meaining that the number of items initially on screen + 1 will be correct while all other ListItems are rearrenged.
In which part of my code do you guys think my problem lies because right now I've been trying to fix this for hours and I'm clueless. All help is very much appreciated.
EDIT:
Here's my getView():
#Override
public View getView(int position, View convertView, ViewGroup parent) {
CountdownItem ci = mTitle.get(position);
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item, parent, false);
holder = new CountdownViewHolder();
holder.mTitle = (TextView) convertView.findViewById(R.id.textPrim);
holder.mSubtitle = (TextView) convertView
.findViewById(R.id.textSec);
holder.mDayProgress = (ProgressBar) convertView
.findViewById(R.id.day_progress);
holder.mMonthProgress = (ProgressBar) convertView
.findViewById(R.id.month_progress);
holder.mYearText = (TextView) convertView
.findViewById(R.id.year_text);
holder.day_help = (TextView) convertView
.findViewById(R.id.day_help);
holder.month_help = (TextView) convertView
.findViewById(R.id.month_help);
holder.setTitle(Integer.toString(position) + " Title");
holder.setSubtitle(ci.getSubtitle());
holder.fixImageAndText(position);
convertView.setTag(holder);
} else {
holder = (CountdownViewHolder) convertView.getTag();
}
return convertView;
}
You aren't using the ViewHolder pattern correctly. The following code needs to be moved outside the if/else clause and before return convertView:
holder.setTitle(Integer.toString(position) + " Title");
holder.setSubtitle(ci.getSubtitle());
holder.fixImageAndText(position);
This is the correct behaviour for the listview when it is reusing cells, the problem is that you only set the values when the cell is first created.
When convertView == null the listview has no cell to recycle. However, once it has created a few it can reuse them to display as you scroll.
What you need to do is set the title and subtitle even when convertView is not null. That way you're setting them for each new list position.
Yes, this is because android reuses views in lists, to increment performance and rendering speed.
The holder pattern is used to store views ids. After you retrieve them, you have to set the text you want to see inside.
For example, you retrieve your data (e.g. myDataArray[position]), and if it's all ok, you proceed setting title, subtitle, dayprogress, etc. with TextView's setText().
Related
I'm new to android programming, and I've been reading a lot about it lately. One of the features of ListView, if I understood it right, is that it recycle views and just replaces it with new data when an item is off the screen.
And just a few minutes ago, I was reading up about endless scrolling, and RecyclerView has been one of the popular choices to implement such a feature. So I looked up RecyclerView, and in this video, it is mentioned that RecyclerView recycles a view automatically to reuse it for new data (as a way to contrast its difference with ListView).
Did I misunderstand ListView about its recycling mechanism? Or if it does recycle, how do you actually implement (or how do you know you are implementing) it?
RecyclerView does recycling automatically. In order to make ListView recycle items you will need to do this modification inside of adapter class.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
//brand new
convertView = LayoutInflater.from(mContext).inflate(R.layout.days_list_item, null);
holder = new ViewHolder();
// below is variables that will be different in your case
holder.numberOfDays = (TextView) convertView.findViewById(R.id.eventDays);
holder.sinceOrUntil = (TextView) convertView.findViewById(R.id.eventType);
holder.eventTitle = (TextView) convertView.findViewById(R.id.eventTitle);
holder.daysText = (TextView) convertView.findViewById(R.id.DaysText);
convertView.setTag(holder);
}
else {
//reusing item
holder = (ViewHolder) convertView.getTag();
}
// rest of the code
}
For more details refer to this link.
We are working with list views in college at the moment. My lecturer gave us a simple application that displays mail messages in a list and when the user selects one it displays the content of the message in a new activity. I understand pretty much all of what is going on but there are a few grey areas I want to clear up!
Basically I am wondering what this section of code does?
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
View v = convertView;
if (v == null) {
LayoutInflater vi = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vi.inflate(R.layout.inbox_row, null);
}
This method is located within a class that extends ArrayAdapter. Am I right in thinking that it is some form of recycling? for when views go on and off the screen?....
Any help is much appreciated. thanks.
it's exactly what you said, a form of recycling.
Inflating a layout takes a lot of memory and a lot of time, so for the efficiency sake, the system passes to you that just went off the screen and you can simply update its text and images and give them back to the UI.
So for example, if your list view is showing 6 items on its list (due to the height of it), it will only inflate 6 items and during scroll it just keeps recycling them.
there's some extra optimisations tricks that you should use and I'm sure that the video link that the commenter posted will explain them.
edit
that example is an ArrayAdapter of Store items, but you can make it to whatever you need.
the adapter does the match and separation layer between UI and data.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null)
convertView = newView();
// Store is the type of this ArrayAdapter
Store store = getItem(position);
Holder h = (Holder) convertView.getTag();
// And here I get the data and address them to the UI
// as you can see, if the convertView is not null,
// I'm not creating a new one, I'm just changing text, images, etc
h.storeName.setText(store.getStoreName());
h.address.setText(store.getAddressLine1());
h.postcode.setText(store.getPostCode());
h.distance.setText(store.getDistance());
return convertView;
}
// I like to separate in a different method when the convertView is null
// but that's me being organisation obsessive
// but it also makes easy to see which methods are only being called the 1st time
private View newView() {
LayoutInflater inf = LayoutInflater.from(getContext());
View v = inf.inflate(R.layout.map_result_list, null);
Holder h = new Holder();
// here we store that holder inside the view itself
v.setTag(h);
// and only call those findById on this first start
h.storeName = (TextView) v.findViewById(R.id.txtLine1);
h.address = (TextView) v.findViewById(R.id.txtLine2);
h.postcode = (TextView) v.findViewById(R.id.txtLine3);
h.distance = (TextView) v.findViewById(R.id.txtDistance);
return v;
}
// this class is here just to hold reference to the UI elements
// findViewById is a lengthy operation so this is one of the optimisations
private class Holder {
TextView storeName;
TextView address;
TextView postcode;
TextView distance;
}
While this question may sound like a dupe of some others, the fact I am trying to do this in a widget significantly limits my ability to use the proposed solutions elsewhere.
Summarized: I would like to add spacing above the top-most item in the list and below the bottom-most item in order to offset them away from the title bar and bottom bar edge.
Essentially, I am trying to solve the same problem as Add margin above top ListView item (and below last) in Android, however, I cannot rely on having a reference to my ListView object in order to setHeader() or anything like that.
Is this really impossible to do in an Android widget?
I assume you are using an adapter for your ListView, so you are inflating additional listview layout. In a getView method, according to list item position (0 and last), place your bottom or top padding.
So ,here i have override function of adapter.From this function you can change or specify margin,height.Here you need to take object of Layout which you are using and from this you can change layout attributes.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
LayoutInflater mInflater = (LayoutInflater) context
.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = mInflater.inflate(R.layout.drawer_list_item, null);
}
if (position == 0) {//for first row
ImageView imgIcon = (ImageView) convertView.findViewById(R.id.icon);
TextView txtTitle = (TextView) convertView.findViewById(R.id.title);
RelativeLayout.LayoutParams relate = new RelativeLayout.LayoutParams(200, 200);
relate.setMargins(150, 0, 0, 0);
imgIcon.setLayoutParams(relate);
RelativeLayout.LayoutParams text = new RelativeLayout.LayoutParams(300, 100);
text.setMargins(150, 180, 0, 0);
}
return convertView ;
//HOPE IT HELP
in the adapter during getView() check if it's either position 0 or .getLength() and set LayoutParams on the convertView there
I have a ListView that I put through a complex bit of coding. The list changes often with different types of data that require different views. On rare occasion, I'll end up with 1 view being reused by Android for a row that's supposed to look different. It seems to only happen when the data being displayed radically changes. I was hoping there was a way to programmatically wipe the ListView's memory clean. Is this possible?
Here is the beginning of my getView:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
SearchHolder holder = null;
int type = getItemViewType(position);
if (null == convertView) {
holder = new SearchHolder();
if (type == SEARCH_TYPE_FREETEXT) {
convertView = mInflater.inflate(R.layout.layout_search_item_freetext, null);
holder.txtText = (TextView) convertView.findViewById(R.id.search_itemname);
holder.vHeaderWrapper = (LinearLayout) convertView.findViewById(R.id.search_headerwrapper);
holder.txtHeader = (TextView) convertView.findViewById(R.id.search_header);
}
else {
if (items.get(position).mData == null) {
convertView = mInflater.inflate(R.layout.layout_loadmoreresults_white, null);
}
else {
convertView = mInflater.inflate(R.layout.layout_search_item, null);
holder.txtText = (TextView) convertView.findViewById(R.id.search_itemname);
holder.vHeaderWrapper = (LinearLayout) convertView.findViewById(R.id.search_headerwrapper);
holder.txtHeader = (TextView) convertView.findViewById(R.id.search_header);
}
}
convertView.setTag(holder);
}
else {
holder = (SearchHolder)convertView.getTag();
}
...
ListView does something called "recycling" when you scroll through a list, and what you will need to do is override the getView() method to update the individual listView item that is being recycled. By default android does not clear out these views. Check out the following link on ListView recycling:
http://mobile.cs.fsu.edu/the-nuance-of-android-listview-recycling-for-n00bs/
Without code it is hard to tell if you already know about this or not, but this is the cause of such problems in my experience.
If you use more than one layout for your list items then I suggest to inflate the appropriate layout from the xml every time in the getView() method.
I have a straight forward BaseAdapter for my ListView. It downloads a JSON feed and displays the data in the rows. There is a ViewHolder which contains the views and a data object called "Story". Everything works just fine.
However, after some scrolling of longer lists, I notice two things.
1) My log shows that the adapter is reloading the feed when scrolling further down. This is strange, as I put the whole JSON array into a variable, so why does it have to reload?
2) More importantly, after some scrolling back and forth, the rows contain the wrong "Story" objects. Here are the relevant parts of the getView routine:
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
Story story = stories.get(position);
if (convertView == null) {
//create holder
holder = new ViewHolder();
convertView = inflator.inflate(R.layout.story_list_item, parent, false);
holder.titleView = (TextView) convertView.findViewById(R.id.story_list_title);
holder.dateView = (TextView) convertView.findViewById(R.id.story_list_date);
holder.story = story;
holder.imageView = (ImageView) convertView.findViewById(R.id.story_list_image);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
// configure the view
holder.titleView.setText(story.title);
return convertView;
}
Simple enough. Now the strange thing is that I can fix the problem by eliminating the if statement if (convertView == null) (and, I presume, eliminating the row recycling as well).
But will I not run into memory problems this way? Why does the plain vanilla version not work?
Thanks for your help.
Regards,
S
You are aware that you're only assigning
holder.story = story
when convertView == null ? Consider moving holder.story = story to just after your convertView if-case and it should work a lot better. Btw, do you even need to store the "story" inside your view holder? Typically that pattern should only be used to store Views and view state information, not the data of the actual position.