I´m facing the implementation of a View where I have to load perhaps almost 100 items in a list. I have a doubt in which maybe the best way to implement it.
I already know that ListView recycles the views and ScrollView keeps all in memory. The point is that I was thinking in apply paging to the Scrollview to avoid huge loading times when the app inflates all items.
Applications as Google+, Facebook, twitter or Linkedin, Do you think they use ListView?
Thanks
ListView is definitely the way to go. It's easier to use than ScrollView, and a paging system doesn't fit in with the style of android.
ListView is meant to create a list of varrying lengths based of an array of information. ScrollView is for having a (usually) set amount of children in the View (defined in the layout xml).
ListViews do not inflate all items, they inflate however many can fit on a page at a time. Your fastest option, with or without paging is a ListView. However, if each child is completeley different, then ScrollView is the way to go.
Related
My question is about best practices in Android in terms of using ScrollView to scroll other views and widgets. This is to know when to use a ScrollView to eliminate redundancy of scrolling if scrolling is possible in a given widget/view/layouts.
So I notice that there are instances where I don't really need to use ScrollView to make things scrollable. Few of the widgets/views/layouts that I know of are TextView and ListView. This is supported according to this documentation.
You should never use a ScrollView with a ListView, because ListView takes care of its own vertical scrolling. Most importantly, doing this defeats all of the important optimizations in ListView for dealing with large lists, since it effectively forces the ListView to display its entire list of items to fill up the infinite container supplied by ScrollView.
The TextView class also takes care of its own scrolling, so does not require a ScrollView, but using the two together is possible to achieve the effect of a text view within a larger container.
My question is, are there other widgets/views/layouts that handles their own scrolling other than the two I have stated above and the documentation has. Maybe there are others that are scrollable or other methods to make things scrollable other than the default of some widgets and by using the ScrollView.
Preferred answers must be base on experience and documentation (other than what I've shown). Thanks in advance for any good answers.
WebView is one other class that does its own scrolling. My "best practice" advice is to use ScrollView to add scrolling to an arrangement (usually vertical) of fixed-size widgets. As you have noted, variable-sized widgets such as ListView provide their own scrolling.
if you read the official documentation you will find that tell you when not to use ScrollView:
You should never use a ScrollView with a ListView, ListView Because Takes Care of Its Own Vertical scrolling. Most importantly, doing all of the defeats esta Important optimizations in ListView for dealing with large lists, since it forces the ListView Effectively to displays its Entire list of items to fill up the container supplied by ScrollView infinite.
More information here.
I'm making sort of a news feed, that is displayed below a static menu. To avoid the news feed from being scrolled in the tiny bit of space that's left after the menu, I wanted to scroll both the menu and the newsfeed at the same time.
Now I'm realizing this with a LinearLayout, so it doesn't scroll itself like the listview. But my question is, is using a LinearLayout, which from what I know doesn't reuse views like a listView, bad practice? How likely am I to get into memory issues, since the news feed can have A LOT of views, and they all contain images.
Many thanks!
Apparently there is a pretty good chance for you to get an OutOfmemmoryexception in no time with this approach,If you want to go with re-using the views
I suggest you should go with the new RecyclerViews in Android,
Go here for a tutorial on recycler views
I don't know if this qualifies to be an answer. But if you are using a LinearLayout with a header view and a ListView inside it, then there are no issues. Since the main worry you have is the news feed which would be recycled by the ListView. Neglecting to use view recycling is asking for trouble, and will likely break after 50 or so (Android hates images).
As for the header that must disappear. I would avoid putting it as the first item in a ListView as suggested in the comments, and rather have it static in the LinearLayout. And use a view translation and/or transparency to hide it. This keeps the option availible to display the header at any point, regardless of the list's scroll.
I'm making a GUI with two different parts. The first part (at the top) is composed of some banners, several fixed buttons. So I think using LinearLayout is the most straightforward way to implement. The second part is composed of several similar items grouped together which can be implemented by using ExpandableListView, I think.
However the problem is that the content exceeds the screen size. So I intend to put two of them into a ScrollView. I checked several sources, it seems that putting "ExpandableListView" inside a ScroolView is NOT possible, or not efficent, so I'm afraid...
Would you help to confirm if this is possible? efficient ?
If no, would you give me some recommendations for this layout design?
I'm indeed looking forward to your supports.
Sincerely.
If you have a fixed header at the top of a list, use ListView's header view feature.
Putting ListViews in ScrollViews fundamentally makes no sense and here is why:
ListView has one purpose: to efficiently display unbounded data sets. Since these can be extremely large (tens of thousands of items and more) you do not want to create a View for each item up front. Instead, ListView asks its Adapter for Views only for the items that currently fit in the ListView's measured space on screen. When an item's View is scrolled out of sight, ListView disconnects that View and hands it back to the adapter to fill out with new data and reuse to show other items. (This is the convertView parameter to an Adapter's getView method.)
ScrollView also has one purpose: to take a single child view and give it "infinite" vertical space to fit within. The user can then scroll up and down to see the full content.
Now given this, how many item Views would a ListView create for a 100,000 item Adapter if it had infinite height available to fill? :)
By putting a ListView inside a ScrollView you defeat ListView's key purpose. The parent ScrollView will give the ListView effectively infinite height to work with, but ListView wants to have a bounded height so that it can provide a limited window into a large data set.
Well Expandable List View itself has scrollable property by placing it in scroll view is really undesirable.As the both scroll would contradict and smooth scrolling can't be obtained in that case..
If we have any data to be shown prior or later to list...
Best way is to use header and footer view to list...
I recommend you use header and footer in your case.
I need to display a complicated list in my app. On each row there will be a checkbox and some TextView.
I know this could be done via ListView/Adapter, but I was worried it requires too much tweaking to make it fits my specific requirement, so I just created my own customized MyListView inheriting LinearLayout. On initiating, it adds MyListViewItem (inherited from RelativeLayout) dynamically.
The customized view functions fine. However, I notice that the rendering speed of MyListView is a little too slow, so I wondered will it be faster if I use ListView/Adapter instead?
Thanks,
The benefit of using ListView rather than a great big LinearLayout is that the OS can do a better job of optimizing when views are inflated, and the recycling of views, based on what is actually visible to the user. It also makes it easier to perform common actions such as scrolling to a particular row.
ListView recycles its items. So, yes, it will work much more efficiently in case of a large number of list items. And as a result you'll obtain a less complicated view hierarchy.
I'm researching creating a view for displaying EPG data. That is the view should:
have a fixed header column that shows the services,
have a fixed header row that shows the time and
a content area that has equal-height TextViews of flexible width for showing the actual EPG entries
Most importantly, scolling vertically must scroll header column as well, scrolling horizontally must scroll header row.
Apart from drawing the whole view myself (inside a scrollable?) I'm totally stumped if there is any good approach I could use involving linear layouts or such.
Any hints are greatly appreciated- please note that I'm and android beginner.
Approach 1: Everything (that is all views) are pre-generated.
Have top and left one-way ScrollViews together with a bidirectional ScrollView and have the scolling be synchronized ( Android: Synchronized scrolling of two different views ). Synchronized scrolling isn't to difficult to do if you've subclassing the ScrollViews and add your own ScrollManager to handle notifications.
Drawback: ScrollViews inside ScrollViews for the main content area do seem to be the desired option. The whole thing will become highly resource intensive as all items need to be created upfront to be available for scrolling.
Approach 1 takes care of view-synchronization for the scrolling, but is a huge resource hog (imagine an EPG with 30+ channels and 100+ events per channel).
Approach 2
One approach for this I could imagine would be- for the main content area- a ListView with a custom ArrayAdapter. Custom adapter would probably return a LinearLayout or similar holding the individual events. That way, scrolling would still work bidirectionally if the ListView is put into horizontal ScrollView and at least the LinearLayouts themselves could be recycled by the ListView.
Are there better approaches?