I have ListView that is populated like so:
ArrayList<MyFullDataClass> myFullDataClassList = Utilities.getDataFromSQLite(getActivity()); // populate list from SQLite
ArrayAdapter<MyFullDataClass> adapter = new ArrayAdapter<MyFullDataClass>(getActivity(), android.R.layout.simple_list_item_1, MyFullDataClassList);
setListAdapter(adapter);
MyFullDataClass contains many things: Name, address, phone, email, web site, etc. So as it is, each row of the list contains all of this information. It's a little busy. I would like to make it so that each row in the list contains only, say, name and email (and then touching the row would popup with all information in MyFullDataClass)
I could do this by creating a class, call it MyPartialDataClass, that contains fields for only name and email, then create an ArrayList<MyPartialDataClass> and copy data from myFullDataClassList to myPartialDataClassList and use this partial class for the adapter. (Then when a row is clicked, use myFullDataClassList.)
Not particularly elegant, but it would work.
Is there a better way?
I don't think there's a need to have two separate classes which ultimately hold the same information.
Having one class to hold necessary information is fine, unless you absolutely need minute efficiency gains of having two classes. What I would do is make your Adapter take a MyFullDataClass object list, but only populate the views with name and email.
From there, you can listen for an onClick event on your Adapter and pass the MyFullDataClass object associated with the clicked view to a fragment which will display the rest of the information associated with the MyFullDataClass object (i.e. the fragment will display address, phone, etc in addition to name and email).
You wouldn't make two separate tables in a database to hold parts of the same information. You would select what rows/properties from each entry that you need. The same concept applies here, IMO.
Related
I'm looking for a view known as LongListSelector on the Windows Phone. It's a list view with group headers. Tapping a group header displays only a list of groups. Tapping a group on the list of groups hides the list of groups and scrolls the view to the selected group. It's a very useful way of groupping long lists with easy navigation between groups. If there are alternatives fit for the same purpose that would be also great.
You can do this easily :)
The first thing you need to do is make sure your data source is a collection of collections. I would suggest an ObservableCollection> if you want maximum binding goodness. Then we can construct our listView as follows:
var listView = new ListView ();
listView.SetBinding (ListView.ItemsSourceProperty, "Data");
listView.ItemTemplate = new DataTemplate (typeof (MyCell));
listView.GroupHeaderTemplate = new DataTemplate (typeof (MyHeaderCell));
listView.IsGroupingEnabled = true;
listView.GroupShortNameBinding = new Binding ("Title");
In order, we first bind in our data, I am assuming the BindingContext here will be inherited from the page. Our data should be the collection of collections already mentioned.
Then we bind in our ItemTemplate as normal, we make a GroupHeaderTemplate, this will be the template shown in the list during normal scrolling. Next we enable grouping to tell the list to use the data as a grouped collection rather than a flat list.
Finally with all that done, we provide a binding for the GroupShortName. This binding is run against the collection for each group to grab out a string (or an object that will have ToString called on it) to produce the jump list as you showed in your screenshots.
For performance reasons you may want to ensure the ItemsSource is not set until everything else has been set to avoid the ListView attempting to realizing Cells in a partially configured state. This will not actually result in bugs, it just forces the ListView to do more work.
Say I have a List<User>. Now I can wrap this list in an ArrayAdapter.
List<User> users = Users.getAll();
ArrayAdapter<User> = new ArrayAdapter<User>(this, android.R.layout.simple_list_item_1, users);
I then bind the adapter to a listview to display the list of Users.
Users.getAll() uses Sugar ORM to query the database and return a list of users. Items can be added to the user list from the activity that displays the user list. I am wondering how do I keep the listview updated.
Option 1
One way is to manually update the users as a I add to the database and then call adapter.notifyDataSetChanged(). This works, but it doesn't feel right because I am maintaining a "fake" list that represents what is in the database.
Option 2
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
Will all the child views be thrown away and be re-rendered? Or does it call the equals() method to see if the models bound to each child is the same and then update only what is new?
Other Info
Since I am using SugarORM, I don't think I can get access to the Cursor to do something more efficient. However if there is a better way to keep the list synced with SugarORM, I am happy to hear that as well.
In answer to your option 2: No, it doesnt call equals, because the adapter works in conjunction with the widget to re-use the views, it doens't create a new view foreach item in the list, it create a view foreach visible item and as you scroll re-uses view that left the screen.
The best option here is to create your own adapter, creating a class extending BaseAdapter and creating your own logic inside it requerying the database and notifying the change to the listview (or gridview)..
On the other hand doing what you said here:
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
isn't bad either.
Create a DAO class that extends Observable, then have your Adapter implement Observer. Now every time you add or remove a SugarRecord, do through the DAO class and whoever is register as the Observer will get notified through the following method:
#Override
public void update(Observable observable, Object o)
You can more about Observable/Observer pattern here. This is just one of the many examples and tutorials out there.
I am new to Android and am trying to get my header round the SimpleCursorAdapter and CursorLoader classes. From my understanding, all of the examples that I have seen use these two classes to load data into a ListView in a background thread (to not block the UI).
I am OK with this and have used this general approach with my own list of items, however I now want to be able to click on an item in the list and get the full information for the item. Is it usual practice to use SimpleCursorAdapter and CursorLoader to retrieve the details for a single item? or are they just meant for lists?.
Thanks.
They are not meant for lists only. You can - and should - use them in detail views (activities) as well.
I've sketched a possible way to do so on my blog:
http://www.grokkingandroid.com/using-loaders-in-android/
Think of Adapters as a layer of abstraction between your data (Cursor) and whatever you attach that Adapter to (ListView for example). This way, you have a common interface between your data (Cursor, ArrayList, whatever) and the View you display that data on (ListView, TableView, etc.), this is helpful because if you later find that you want to access your data through an ArrayList rather than a Cursor, then you simply swap out the adapter with a different one and you're ready.
Now considering your question, Adapters give an abstract access to information, therefore you can "ask" it for what information is stored and where. You could attach an OnItemClickListener to your ListView and then access your data from there.
First off I'm really new to android (< 4 days).
I'm trying to wrap my head around how database data is linked to Views and widgets.
I've done a few tutorials and I've noticed that Adapters are used to link AdapterViews which are (as I understand it) Views which contain a bunch of identical subviews (eg lists, gallery, etc). So the Adapter is responsible for creating those subviews and populating the data for each one (correct me if I'm wrong).
Now let's say I have a list view which lists Hotels for example. Each row in the list has the Hotel's name and a basic rating (eg 5 star). Now when you tap on a hotel in the list a new activity shows up showing the details of that particular hotel. All the data is in a database. I understand that you have an adapter manage the data<->view link for the list, but what's the best way to then manage data for the hotel details view (which is not a list but just a couple of text views and an image for example)?
Is it best to just pass the ID in the intent and then have the details activity fetch the data from the DB on its own (in this case do I store the query in the details activity?)? Or do you get all the fields you need and put those in the intent directly? Do you need an adapter for a view which doesn't actually generate lots of similar subviews?
I guess a summary of my question is what do you use instead of an adapter when you're not dealing with adapterviews but just simple straightforward single views.
Thanks for any help you can provide.
Is it best to just pass the ID in the intent and then have the details activity fetch the data from the DB
on its own (in this case do I store the query in the details activity?)?
That is what I would recommend.
Do you need an adapter for a view which doesn't actually generate lots of similar subviews?
No. You only use an Adapter with an AdapterView (ListView, Spinner, etc.)
I guess a summary of my question is what do you use instead of an adapter when you're not dealing with
adapterviews but just simple straightforward single views.
Just the Cursor from the database. Get the fields from the (one) row in the Cursor, put them in the EditText widgets, and when the user makes changes, update the row.
#CommonsWare is bang on. As a code example, I was able to DRY things up by creating a helper method to dynamically set the TextViews a little cleaner.
In my onCreate() I have a number of the following lines:
bindTextView(hotel, "uid"); // `hotel` is the Hotel object with attributes.
And then I define bindTextView() below as follows:
protected void bindTextView( Hotel hotel, String attribute ) {
try {
// Get field for object dynamically.
Field field = hotel.getClass().getField(attribute);
// Invoke field "getter" method to get value.
String value = field.get(hotel).toString();
// Get resource id dynamically.
int resourceId = R.id.class.getField(attribute).getInt(null);
// Get element with resource id.
TextView element = (TextView) this.findViewById( resourceId );
// Finally, set the element's text value.
element.setText( value );
} catch (IllegalAccessException e) { e.printStackTrace();
} catch (NoSuchFieldException e) { e.printStackTrace(); }
}
I actually moved this helper method to a base Activity class since it's shared amongst a number of different activities.
I hope that helps some people keep their activities clean.
JP
I am new to android programming, but I am trying to learn. I have written some code that takes in some parameters through a "normal" view with checkboxes and textviews. Then I use this information to generate a lot of numbers that I want to display in a listview. I have managed to create a listview when I press a run button, but how do I pass the information from the main view to the listview. Is it best to pass the information one number at the time or a large array with all the numbers. The list of numbers can be really large.
What you probably what to do is create an adapter with the numbers as the data source. If the numbers are in an array you can create a new ArrayAdapter and set the ListView adapter as that adapter:
ArrayAdapter adapter = new ArrayAdapter<Double>(getApplicationContext(), R.id.id_of_textbox, arrayOfDoubles);
listView.setAdapter(adapter);
In this code I've assumed the numbers are doubles, however ArrayAdapter is a generic class so it can be any object contained in the array. The array can also be presented as a List (like an ArrayList).
Hope that helps you out. Here are some bit of documentation to read and some good video sessions to watch:
ArrayAdapter
ListView.setAdapter()
The World of ListView Google I/O 2010 Session
How big is the array can get?
Most likely that displaying the list as another activity and passing the data as intent's extra will be the solution.