I got into a situation where I have a ScrollView with some elements, where one of those elements is a table with many rows. I don't want my app to be laggy or use too much memory, so I thought it would help performance to use a RecyclerView for the table. But we all know the rule: Never put a scrollable view inside another scrollable view. So I searched a bit, and found this question, where the accepted answer was to fix the size of the recyclerview.
Now my question is: Does this still improve performance? As far as I know, a RecyclerView recycles it's elements by reusing the elements that are not visible because the user scrolled down. But does it still do this if we forbid the RecyclerView to scroll and use it's parent (ore parents parent) to scroll?
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I understand we always use listview to display list of items instead of Scrollview. But I know we can do it with scrollview also. I understand that performance of list view is better than ScrollView when you want to display list of items. My question is there are any reason for that also? And why nobody use scrollview to display list of items? Please give me your opinion. Thank you.
I often use Scrollview for displaying a limit of items, this number rarely be changed on runtime, such as in a configuration page. Otherwise, ListView is for display a lot of items. Those items may be the same type such as a list of Students, Messages, etc.
ListView uses a concept of dequeueing that is removing view from the view hierarchy when they are not visible. For example if you have 20 items and only 10 are visible at a time.
The listview will remove the top 1st element when 11th element comes
into view using scrolling. This reduces memory load and gives smoother
performance. Battery consumption is major factor of phone these days
and no one wants a app that consumes all the phone battery.
Scrollview on the other hand keeps all the view added in it in the view heirarchy all the time therefore increased memory usage and performance issues when the number of views added are huge.
ScrollView is used to put different or same child views or layouts and the all can be scrolled.
ListView is used to put same child view or layout as multiple items. All these items are also scrollable.
A scrollview on the other hand is quite different. You add other views to a scrollview which allows you to have more elements than what would fit on screen. Say, for example, you wanted to have 50 buttons or a large chunk of text. By using a listview you have a container that is the size of the screen but allows the user to scroll up and down to see the other views.
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 know this question has been asked many times, and I have looked everyone of them here but none of which helped me.
What I am trying to do is to mimic the UI from iOS where you have a UITableView with cells that are UICollectionView. The cells are images that page horizontally. I am trying to do this with a listview of viewpagers.
My current solution is I create each row before hand. It is a linearlayout with a title, the viewpager, and two buttons on the bottom. I already created the adapters for the viewpagers as well. In the getView method of listview, I just return the view in the created collection based on the position as the index. I know this is bad practice, it uses a lot of memory, but the method is just one line.
I have tried the viewholder pattern, but only some rows in the listview will get the viewpager. The recycling mechanism doesn't really help in my situation, so I sacrifice more memory for the same effect.
So I can see all the viewpagers in my listview. The problem now is that only the bottom 2 are able to page from iamge to image. The ones on position 0,1,2, couldn't. I thought it has to do with listview intercepting the events, but how come the ones on the bottom work perfectly??
Any help is appreciated!
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'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?