Custom Array Adapters Creating an Event Listener 1
- Slides: 24
Custom Array. Adapters Creating an Event Listener 1. 2. 3. 4. In-class App: Contact App using our own custom Array. Adapter Lab 5 Part 4. On. Click. Listener Interface. Creating an Event Listener. Complete the App from Lab 5 Part 4.
In-class App This app will help Moquelumnan language students practice their number (1 -10) skills. 1. Each number includes an image, the written English name, the numeric value, and an audio sound that will play when the user taps directly on the list item. 2. The activity_number layout must produce a scrollable listing without using a Scroll. View. Use a List. View powered by a custom Array. Adapter. 3. The audio and image files can be downloaded from the website.
Explore On. Click. Listener Question: What did you find?
Explore On. Click. Listener Question: What did you find? Answer: • On. Click. Listener is an interface. • on. Click() is the abstract method. NOTE: Implementation for abstract methods is intentionally left blank so that a developer wanting to use the interface can provide their own specific instructions for it.
Review of Classes and Interface Concrete class: if you come across a concrete class in Android you can use it right away. Abstract class: This is a partially implemented class and it contains states and some methods that are fully implemented. Some methods are left abstract so that coders can define the behavior as they choose. Interface: If you come across an interface, you need to provide code for all the abstract methods. Think of these elements as a continuum where an interface is not implemented at all, an abstract class is partially implemented, and a concrete class is fully implemented.
Concrete Class public class Text. View{ String m. Text; int m. Text. Color. ID; void set. Text( String str){ m. Text = str; } void set. Text. Color ( int color) { m. Text. Color. ID = color; } } ….
public abstract class View. Group { int n. Child. Count; Abstract Class void add. View (View view){ add. View. Internal (view, -1); n. Child. Count++; } void remove. View (View view) { remove. View. Internal (view); n. Child. Count--; } void on. Layout() ; } ….
Interface public interface On. Click. Listener { } void on. Click (View view);
Creating an Event Listener 1. As a mobile developer, you will need to set up event listeners for the input events you want to handle. 2. In a simple app, you can easily utilize the on. Click property for a given view in your layout.
Explore on. Click • The on. Click() method is a callback method. • on. Click() is automatically invoked when a registered event is triggered. • on. Click() has exactly one parameter, the View object being clicked on. • NOTE: Remember, for an interface, you need to provide for all the abstract methods.
How to set up an Event Listener?
In Main. Activity. java 1. Attach the listener to a View. 2. Create new object instance of event listener. 3. Define the event listener inline (and the custom behavior for then the event is triggered. button. View. set. On. Click. Listener(new View. On. Click. Listener() { @Override public void on. Click(View v) { Toast. make. Text(view. get. Context(), “Hello”, Toast. LENGTH_SHORT). show(); } });
Numbers App: Event Listener • In the Numbers App, it is less clear which View has triggered a listener event. • Research On. Item. Click. Listener. What did you find?
1. On. Item. Click. Listener is an interface definition for a callback to be invoked when an item in an Adapter. View has been clicked. 2. There is only one public method. This method is a callback method, on. Item. Click().
Quick Review Similarities set. On. Click. Listener vs. set. On. Item. Click. Listener: Both of these register a listener that will trigger an event. On. Click. Listener vs On. Item. Click. Listener: Both are interfaces for abstract listener events. on. Click vs on. Item. Click: Both are abstract methods for handling a listener event.
Quick Review Differences on. Item. Click: A Callback method to be invoked when an item in an Adapter. View has been clicked. on. Click: A Callback method to be invoked when a View within an Activity layout has been clicked.
Tasks for implementing an Event Listener for List. View+Array. Adapter: 1. Register a listener using set. On. Item. Click. Listener. 2. Implement on. Item. Click() from On. Item. Click. Listener(). 3. Call get. Item (position) to access the object clicked. on. Item. Click() parameters:
// CREATE AN ADAPTER AND LOAD IT WITH DATA OBJECTS // ATTACH THE LISTVIEW TO THE ADAPTER Number. Word. Adapter items. Adapter = new Number. Word. Adapter(this, words); list. View. set. Adapter(items. Adapter); //CREATE AN EVENT LISTENER TO RESPOND TO A CLICKED LISTVIEW ITEM list. View. set. On. Item. Click. Listener(new Adapter. View. On. Item. Click. Listener() { @Override public void on. Item. Click(Adapter. View<? > adapter. View, Adapter. View where the click happened. View view, The view within the Adapter. View int position, that was clicked. long l) { The position of the view in the adapter. }); } } String my. Word = words. get(position). name); The row id of the item that was clicked
Experiment with the Numbers App. Display a Toast containing the audio id of a clicked List. View item.
Review Media. Player Examine Media. Player documentation Question: What are the different states that we can transition between as the media player plays a sound file?
• The media player object is initially in an idle state. It is sitting there Idle, waiting for instructions. • In the Prepared state, a song has been assigned. The media player is preparing to play a certain audio file. No sounds are made. • In Started state the media player is playing an audio file. • Pause state will produce a pause. From the Paused state can return to Started state to resume where an audio was left off. • Stop can halt the audio. Once stop the media player has stopped, it can’t be resume. It needs to enter the Prepared state.
Handling Touch Events on a List. View
Complete the Moquelumnan language app.
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