I am developing an app and am looking for some general guidance:
The app is a memory trainer, and will have a couple of different modes:
Numbers: Up to 400 digits will be displayed on the screen in a gridlike pattern
Faces: Images of faces will appear, approximately 9 to a page, also in a grid pattern
The question is: can I accomplish this with a single xml layout file, and should I use the same layout type for each (and if so, what should it be!) ? It's a large app, so consistency would be heavenly.
I would prefer a layout with flexibility, and I am leaning toward GridView right now.
Any thoughts?
A Grid view is basically like a list view where items are arranged in a static grid.
It retrieves views from the Adapters as scrolled by user.
A table layout is a layout manager and does not do scrolling if required.this means u have to put it inside a scroll view. This implies that all of the data you are displaying must be populated into the TableLayout up-front, so the ScrollView knows the total space it is to scroll in. It also does not directly give you per-"item" selection or interaction, because a TableLayout doesn't have items, it is just a layout manager.
Also Adapter -based view should be used where significant amount of data is there to be scrolled. So it seems that grid view would be more suitable in the situation u r working.
Related
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.
I have an app which loads a boatload of images and displays them in a TableLayout which is inside a ScrollView. At run time I get the width of the layout parent and use that to determine how many images can go in each TableRow (all of the images are of a set size).
I'm concerned about memory issues when loading more and more images. I know ListView recycles its views but I don't know how to dynamically change number of views in each item. I am only aware of inflating XML which isn't going to change the number of views per item at run time.
So my question is what is easier - figuring out how to recycle views in my table by myself, or making a list's items change based on screen size? Just a link to a tutorial on how to do whichever is easier is good enough an answer for me.
I suggest you to use ListView with the ViewHolder approach (you can see it here: How to load the Listview "smoothly" in android).
The ListView, when scrolled, removes the views that are no more visible and gets the views that are about to become visible. This way, it's better than using a ScrollView and a TableLayout.
Can any one explain the difference between Scroll View and List View? When to use which one? And which one is more efficient?
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.
Simply ScrollView is for both homogeneous and heterogeneous collection. ListView is for only homogeneous collection.
They're completely different.
A ScrollView is simple a scrolling container you can use to scroll whatever you put inside it, which might be a list of items, or it might not.
http://developer.android.com/reference/android/widget/ScrollView.html
A ListView is very specifically designed to hold lists, where items typically look the same (or at least follow a pattern, e.g. section headings). ListView is also designed to connect to a data source of some sort, SQLite, array, content provider etc. ListView can scale to handle enormous numbers of list items.
http://developer.android.com/resources/tutorials/views/hello-listview.html
If you have data you need to show in a list, use a ListView. If you just need scrolling content, then a ScrollView is probbaly enough.
ListView:-
In ListView You can manage layout of items in xml easily that you want to display in list.
You are required to tell the adapter ho many item you want in your display list.
You can design for both homogenous as well as heterogenous views depending on your requirement by overrifing getItemViewType() method of Adapter.
In ListView items in list are created according to screen size. i.e How many items can appear on screen are created additional views(items) are created when list is scrolled at runtime. The views that are displayed once are cached when they move out of screen and when list is scrolled back to previous state the same views are displayed but this time view are not created rather they are fetched from cache.
ScrollView :-
Cache concept is not applicable with ScrollView.
All views are created at once when they come to screen and are not cached when they move out of screen while scrolling. They are present in memory(main) that may lead to memory leak because the number of objects created are not being destroyed by garbage collector since they are being referenced untill you are on same page.
Although you can create both homogenous as well as heterogenous views. If there are more items to be displayed in your list it would be tedious to manage the layout whether you are designing in xml or creating dynamically using Java code.
It is preferable to use scrollview if you have a single page that does not contain list of items e.g registration form, reservation form but that view is larger than the screen size then put ScrollView as parent view also keep in mind that ScrollView can have only one direct child layout/view.
ScrollView simply places its contents in a scrollable container, you can edit it's contents only by adding views to it.
ListView is a class that uses an adapter which handles creating the views for your data objects, you only need to edit the data, and the layout modifications are done automatically by the adapter.
ScrollView should be used when you have a screen (ex: a form with multiple fields) that do not fit into one screen on small devices, as such scrollview offers the user the possibility to scroll down.
ListView should be used when representing sets of data.
You can read about these at http://developer.android.com/guide/index.html
A ListView is backed by an Adapter, which contains a DataSource. This allows you to easily display data in rows.
A ScrollView allows you to put content inside of it, and if the content exceeds the size of the ScrollView, it will allow the user to scroll.
They both have their uses, but it depends on what you are trying to do.
Since an image worth a thousand words, here are perfect real life examples:
Listview is like the Kijiji app
Scrollview is like the EBay app
Also, see a scrollview like a billboard or a wall, where you can put bunch of different stuff on it.
And a listview is more like a result page: results are all of same nature, therefore they fit perfectly in a listview. Like a contacts list: they all share the same structure; phone number name address, etc....
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?