Basic Functionality in Android

1. Basic Functionality in Android

2. Functionality in Android • Events in Java • mouse related • mouse clicked • button down or up • mouse entered • many others • key pressed • item selected (checkbox, table, list box) • tabbed pane selection made • others…

3. Tying a method to a Button • 3 approaches • By implementing the OnClickListener interface • By using an anonymous inner class • Most common • Same way it is done in typical Graphical programming • Within xml

4. .xml file used in following examples <?xml version="1.0" encoding="utf-8"?> <LinearLayoutxmlns:android=“http://schemas.android.com/apk/res/android” … <Button android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Print Hello" android:id="@+id/pb1" /> <Button android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Print Goodbye" android:id="@+id/pb2" /> <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/et1" /> </LinearLayout>

5. Approach 1Implementing the OnClickListener interface

6. Implementing OnClickListener • OnClickListenerInterface • android.view.View.OnClickListener • one abstract method: public abstract void onClick (View v); • widget must ‘listen’ for this event

7. Implementing OnClickListener • Implementing the interface and “Listening” for the event public class OnClickWithSwitch extends Activity implements OnClickListener { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); View button1 = findViewById(R.id.pb1); button1.setOnClickListener(this); View button2 = findViewById(R.id.pb2); button2.setOnClickListener(this); }

8. Implementing OnClickListener • Implementing onClick() public void onClick (View v) { switch (v.getId()) { case R.id.pb1: ((TextView)findViewById(R.id.et1)).setText("Hello"); break; case R.id.pb2: ((TextView)findViewById(R.id.et1)).setText("Goodbye"); break; default: ((TextView)findViewById(R.id.et1)).setText("Nothing"); } } }

9. Method 2Using an anonymous inner class

10. Using an anonymous inner class • With anonymous inner class • OnClickListener not explicitly implemented • Each widget must still ‘listen’ for the event • when the listener is set, an anonymous inner class is used • inner class is a subclass of OnClickListener • onClick is implemented • Each widget implements functionality accordingly

11. Using anonymous inner class • Utilizing an anonymous inner class public class OnClickWithInner extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); (findViewById(R.id.pb1)).setOnClickListener(new OnClickListener () { public void onClick (View v) { ((TextView)findViewById(R.id.et1)).setText("Hello"); } }); (findViewById(R.id.pb2)).setOnClickListener(new OnClickListener () { public void onClick (View v) { ((TextView)findViewById(R.id.et1)).setText("Goodbye"); } }); } }

12. Method 3Implementing onClick via XML

13. Using onClick XML attribute • With XML • onClick is an attribute in XML • Attribute value is set to the name of the method that is tied to the button • android:onClick=“methodName” • Method is written with the following signature: • public void methodName(View v)

14. Using onClick XML attribute • .xml file used in the following example: <?xml version="1.0" encoding="utf-8"?> <LinearLayoutxmlns:android=“http://schemas.android.com/apk/res/android” … <Button android:layout_width=“match_parent" android:layout_height="wrap_content" android:text="Print Hello" android:id="@+id/pb1“ android:onClick=“displayHello“ /> <Button android:layout_width=“match_parent" android:layout_height="wrap_content" android:text="Print Goodbye" android:id="@+id/pb2“ android:onClick="displayGoodbye" /> <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/et1" /> </LinearLayout>

15. Using onClick XML attribute • Implementing the methods named in XML public class OnClickWithXML extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } public void displayHello(View v) { ((TextView)findViewById(R.id.et1)).setText("Hello"); } public void displayGoodbye(View v) { ((TextView)findViewById(R.id.et1)).setText("Goodbye"); } }