Android Event Handling for GUI

Two kinds of events dealing with Interface: 1) View level (GUI components) AND 2) Activity Level

 

View Level GUI Event Handling

 

Typically the View element involved with have a method that will let you register event handling code for it

Example:

main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Your Name" /> <EditText android:id="@+id/txt1" android:layout_width="214dp" android:layout_height="wrap_content"/> <Button android:id="@+id/btn1" android:layout_width="106dp" android:text="OK" android:layout_height="wrap_content"/> <Button android:id="@+id/btn2" android:layout_width="106dp" android:text="Cancel" android:layout_height="wrap_content"/> </LinearLayout>

TwoButtonEventHandlingActivity.java -- HERE have one listener for both buttons, so does the same thing if either hit...see below for alternative package grewe.twobutton; //import android.R; import android.app.Activity; import android.os.Bundle; import android.widget.Button; import android.widget.Toast; import android.view.View.OnClickListener; import android.view.View; import android.util.Log; public class TwoButtonEventHandlingActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //grab buttons Button btn1 = (Button) findViewById(R.id.btn1); Button btn2 = (Button) findViewById(R.id.btn2);                                                                 //register the anonymous class instance btnListener as handler btn1.setOnClickListener(btnListener); btn2.setOnClickListener(btnListener); } //create anonymous class to handle events of button clicked private OnClickListener btnListener = new OnClickListener() {                                                          public void onClick(View v) { Toast.makeText(getBaseContext(), ((Button)v).getText() +" was clicked", Toast.LENGTH_LONG).show();                       } }; }

ALTERNATIVE --- HAVE A DIFFERENT LISTENER FOR EACH BUTTON

main.xml --- SAME!!   AFTER HITTING CANCEL package grewe.twobutton; import android.app.Activity; import android.os.Bundle; import android.widget.Button; import android.widget.Toast; import android.view.View.OnClickListener; import android.view.View; import android.util.Log; public class TwoButtonEventHandlingActivity extends Activity { /** Called when the activity is first created. */ Button btn1,btn2; @Override public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.main);         //grab buttons     btn1 = (Button) findViewById(R.id.btn1);     btn2 = (Button) findViewById(R.id.btn2);     //register the anonymous class instance btnListener as handler     btn1.setOnClickListener(btnListener1);         btn2.setOnClickListener(btnListener2); } //create anonymous class to handle events of button 1 clicked private OnClickListener btnListener1 = new OnClickListener() { public void onClick(View v) { Toast.makeText(getBaseContext(), ((Button)v).getText() +" was clicked", Toast.LENGTH_LONG).show(); } }; //create anonymous class to handle events of button 2 clicked private OnClickListener btnListener2 = new OnClickListener() { public void onClick(View v) { Toast.makeText(getBaseContext(), ((Button)v).getText() +" inside btn2", Toast.LENGTH_LONG).show(); } }; }

 

Activity Level Event Handling

The following methods can be applied to specific View components but, can also, be to an Activity (or some in Fragment) when the corresponding event is not focused on a specific View component. You can OVERRIDE these methods in your Activity (some in Fragments) to recieve the events and handle them. See android api and book for examples or online.