Since repetition is the mother of all
learning and the following example is one of the most distinct
examples of how to start android
development I wrote it down as well
to try to explain it as best as I can.
What we are going to do is a ToDo
List app.
Bearing the design in mind will help us
better understand what components will be needed ( plus I prefer a
more visualized approach
to such kind of problems ).
As we can see from the mockup sketch
two fragments are needed. One will just display an EditText widget
and when the user clicks
'Send' on the software keyboard we will
pass the text to the list bellow. That gets us to the second fragment
which is a ListFragment.
Both of them are in the MainActivity.
Since we are using a ListFragment we
have to use an Adapter to bind the data to the list.
Also we will need a data model for our
todo items. Lets name it DataItem class.
Last but not least we will create a
custom view from each list item.
Let me summarize things a little bit : We have one MainActivity class with its layout, composed of two
fragments ( one is a ListFragment ). The ListFragment also needs an
Adapter class. Our data model will only need a String variable and a
Custom View for each ListFragment's item for the time.
So let's start from our model. We only
need one getter and one setter method since our only variable will be
a String. You can check the code here .
Now its time to create the TopFragment.
As you can see
the layout is just an EditText. We inflate that layout in onCreateView method ( like we do with every fragment ). The “tricky” part here is adding an OnEditorActionListener so we can listen for the 'SEND' action, get the user input and clear the text in EditText. An Interface is also necessary so we can implement it on the MainActivity and get the user's text input. All of these data will be stored on an ArrayList in the MainActivity and passed to the Adapter to bind them to the view.
The
TaskListAdapter gets each item from the ArrayList as we said above,
creates a new list item and sets the data.
ListFragment
just inflates the layout which consists of a ListView with the
android:divider
atrribute
set to null so we don't have to deal with the default divider line
from the ListView widget.
Since
each item is just a TextView our custom view needs to extend a
TextView. We saw on a previous post how to
create a custom view so I will not go into details.
The
XML layout file for the custom view, used by the TaskListAdapter is:
That input along with the id resource of the XML file that represents the list
item are passed to the Adapter.
The code is below :
public class MainActivity extends Activity implements TopFragment.OnItemAddedListener {
private ArrayList todoItems;
private TaskListAdapter aa;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Get references to the Fragments
FragmentManager fm = getFragmentManager();
TaskListFragment todoListFragment =
(TaskListFragment)fm.findFragmentById(R.id.TaskListFragment);
// Create the array list of to do items
todoItems = new ArrayList();
// Create the array adapter to bind the array to the ListView
int resID = R.layout.tasklist_fragment;
aa = new TaskListAdapter(this, resID, todoItems);
// Bind the array adapter to the ListView.
todoListFragment.setListAdapter(aa);
}
public void onNewItemAdded(String newItem) {
DataItem newTodoItem = new DataItem(newItem);
todoItems.add(0, newTodoItem);
aa.notifyDataSetChanged();
}
}
The method onNewItemAdded() adds the DataItem before every other ArrayList item and also notify the data set has changed.
You can find the code of the project in the github repo here and you can import it and run it on your eclipse.
This example is based on Reto Meier's example on chapter four of his book "Professional Android 4 Application Development" you can find in this link
.png)
