Module 4 user interfaces activity

Android Basic CourseCreating layout classes by using source code – xml layout built-in source code public class HelloAndroid extends Activity { /** Called when the activity is first cre

Android Basic Course

M.Sc Bui Tan Loc btloc@fit.hcmus.edu.vn

Department of Software Engineering, Faculty of Information Technology, University of Science – Ho Chi Minh City, Viet Nam

Module 4: User Interfaces

Section 2: Activity

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High-level diagram class of the Android View API

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View

ViewGroup Activity

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Objectives

• After completing this section, you will able to:

• Create an activity with loading layout form xml-based layout file

• Manage the activity lifecycle

• Start or shut down an activity

• Create resources of many types of menus

• Handle menu item selections

• Use event handlers

• Use event listeners

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Contents

• Activity overview

• Activity skeleton code

• Activity lifecycle

• Different types of menus

• Creating a menu resource

• Common Activity’s methods for working with menus

• Common Menu’s methods for working with submenus

• Common MenuItem’s methods for working with menu items

• User Input events

• Using event handlers

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activity for reading emails

called views

how they interact with each other and with other applications.

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Designing layout by using xml layout text editor

<?xml version="1.0" encoding="utf-8"?>

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Designing layout by using xml layout GUI editor

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Loading layout from xml-based layout file

package com.example.helloandroid;

import android.app Activity ;

import android.os Bundle ;

public class HelloAndroid extends Activity { /** Called when the activity is first created */

Android Basic Course

Creating layout classes by using source code – xml layout built-in source code

public class HelloAndroid extends Activity {

/** Called when the activity is first created */

@Override

public void onCreate( Bundle savedInstanceState) {

super onCreate(savedInstanceState);

TextView tv = new TextView ( this );

tv.setText( "Hello, Android" );

LinearLayout linear;

linear = new LinearLayout( this );

linear.setOrientation( LinearLayout VERTICAL );

linear.setLayoutParams(new LayoutParams ( LayoutParams FILL_PARENT , LayoutParams FILL_PARENT ));

linear.addView(tv);

setContentView(linear);

}

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High-level diagram of activity

• Views and other Android components use strings, colors, styles, and graphics, which are compiled into a binary form and made available to applications as resources

• The automatically generated R.java provides a reference to individual resources and is the bridge between binary references and the source code of an Android

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Activity skeleton code

public class ExampleActivity extends Activity { @Override

public void onCreate( Bundle savedInstanceState) { super.onCreate(savedInstanceState);

// The activity is being created.

} @Override

protected void onStart() { super.onStart();

/ / The activity is about to become visible.

} @Override

protected void onResume() { super.onResume();

// The activity has become visible (it is now "resumed").

}

…

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Activity skeleton code

protected void onStop() { super.onStop();

// The activity is no longer visible (it is now "stopped")

} @Override

protected void onDestroy() { super.onDestroy();

// The activity is about to be destroyed.

}

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The activity lifecycle

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Android Activity main lifecycle methods and their purpose

onCreate() Called when the Activity is created Setup is done here Also provided is

access to any previously stored state in the form of a Bundle.

onRestart() Called if the Activity is being restarted, if it’s still in the stack, rather

than starting new.

onStart() Called when the Activity is becoming visible on the screen to the user.

onResume() Called when the Activity starts interacting with the user (This method

is always called, whether starting or restarting.) onPause() Called when the Activity is pausing or reclaiming CPU and other

resources This method is where you should save state information so that when an Activity is restarted, it can start from the same state it was in when it quit

onStop() Called to stop the Activity and transition it to a nonvisible phase and

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Another activity lifecycle diagram

• In the foreground phase , the Activity is viewable on the screen and is on top of everything else.

• In the visible phase , the Activity is on the screen, but it might not be on top and interacting with the user.

• The entire lifecycle phase refers to the methods that might be called when the application isn’t on the screen,

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The onSaveInstanceState() function

• Whenever an activity is about to be killed, the

onSaveInstanceState() function is called Override this

to save relevant information that should be retained.When the activity is then recreated, the

function (or onCreate() ) to retrieve the saved information.

• The onSaveInstanceState() function is distinct from

in front of the activity, the onPause() function is called Later, if the activity is still paused when the OS needs

to reclaim resources, it calls onSaveInstanceState()

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Activity Life Cycle Sample

• Open Child Activity

> onCreate(null) -> onStart() -> onResume() -> [Open Child Activity]

> onSaveInstanceState() -> onPause() -> onStop() -> [Close Child Activity]

> onRestart() -> onStart() -> onResume()

• Transparent View

> onCreate(null) -> onStart() -> onResume() -> [Open Transparent View]

> onSaveInstanceState() -> onPause() -> [Close Transparent View]

> onResume()

• Turn Display

> onCreate(null) -> onStart() -> onResume() -> [Turn Display]

> onSaveInstanceState() -> onPause() -> onStop() -> onDestroy() ->

[Recreate]

> onCreate() -> onStart() -> onRestorInstanceState() -> onResume()17

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Activity Life Cycle Sample

> onCreate(null) -> onStart() -> onResume() -> [Home Button]

> onSaveInstanceState() -> onPause() -> onStop() -> [Start App]

> onRestart() -> onStart() -> onResume()

• Phone call interrupt

> onCreate(null) -> onStart() -> onResume() -> [Phone Call]

> onSaveInstanceState() -> onPause() -> onStop() -> [Hang Up or press Back]

> onRestart() -> onStart() -> onResume()18

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Starting an activity for passing no values

• Starting an activity for passing no values:

Intent intent = new Intent ( this , SignInActivity class );

startActivity(intent);

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Starting an activity for passing values

• Starting an activity for passing values by putting values into intent object:

//SignInActivity

public static final String NAME_KEY = “name” ;

public static final String PASS_KEY = “pass” ;

…

Intent intent = new Intent ( this , OrderActivity class );

intent.putExtra( this NAME_KEY , nameValue);

intent.putExtra( this PASS_KEY , passValue);

startActivity(intent);

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Catching passed values

//OrderActivity

…public void OnCreate(…){

Bundle extras = getIntent().getExtras();

String usrName = extras.getString(SignInActivity.NAME_KEY);

String passWord = extras.getString(SignInActivity.PASS_KEY);

…}21

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Starting an activity for results

//NoteList Activity

public static final int ACTIVITY_CREATE = 0;

public static final int ACTIVITY_EDIT = 1;

…//Open creating note screen

Intent i = new Intent(this, NoteEdit.class);

startActivityForResult(i, ACTIVITY_CREATE);

…//Open editing note screen

Intent i = new Intent(this, NoteEdit.class);

startActivityForResult(i, ACTIVITY_EDIT);

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Catching returned results

mDbHelper.updateNote(mRowId, editTitle, editBody);

} fillData();

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Shutting Down an Activity

• Returning no results:

finish();

• Returning result cancelled:

setResult( RESULT_CANCELLED , null );

finish();

• Returning result ok:

Intent mIntent = new Intent ();

mIntent.putExtras(…);

setResult( RESULT_OK , mIntent);

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Shutting Down an Activity

• You can also shut down a separate activity that you previously started by calling finishActivity() This method is used for shutting down an activity being in the foreground.

startActivityForResult(intent, requestCode);

try { Thread.sleep(3500);

}

catch (InterruptedException e) { e.printStackTrace();

}finishActivity(requestCode);

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Different types of menus

an activity, which appears when the user touches the MENU button.

• Android 3.0 or later provides the Action Bar, as "action items” to quick access to select menu items

when the user touches and holds a view that's registered to provide a context menu.

when the user touches a menu item that contains a nested menu.

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Different types of menus

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Creating a menu resource

• To create a menu resource, create an XML file inside your project's res/menu/ directory and build the menu with the following elements:

• <menu>: Defines a Menu, which is a container for menu items A

<menu> element must be the root node for the file and can hold one

or more <item> and <group> elements

• <item>: Creates a MenuItem, which represents a single item in a menu This element may contain a nested <menu> element in order to create a submenu

• <group>: An optional, invisible container for <item> elements It allows you to categorize menu items so they share properties such

as active state and visibility

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Creating a resource of menus

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Creating a resource of menus with submenus

<? xml version ="1.0" encoding = "utf-8" ?>

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Creating a resource of menu groups

<?xml version="1.0" encoding="utf-8" ?>

<menu xmlns:android="http://schemas.android.com/apk/res/android" >

<item android:id="@+id/item1"

android:icon="@drawable/item1"

android:title="@string/item1" />

<group android:id="@+id/group1" >

<item android:id="@+id/groupItem1"

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Creating a resource of checkable menu items

<menu

xmlns:android="http://schemas.android.com/apk/res/android" >

<group android:checkableBehavior="single" >

<item android:id="@+id/red"

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Common Activity’s methods for working with menus

• Creating menu items:

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Common Menu’s methods for working with submenus

• A menu group is a collection of menu items that share certain traits With a group, you can:

• Show or hide all items with setGroupVisible()

• Enable or disable all items with setGroupEnabled()

• Specify whether all items are checkable with setGroupCheckable()

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Common MenuItem’s methods for working with menu items

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Loading an options menu resource – Inflating an options menu resource

@Override

public boolean onCreateOptionsMenu(Menu menu) {

super.onCreateOptionsMenu(menu);

MenuInflater inflater = getMenuInflater();

inflater.inflate(R.menu.game_menu, menu);

return true;}

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Loading a context menu resource – Inflating a context menu resource

@Override

public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {

super.onCreateContextMenu(menu, v, menuInfo);

MenuInflater inflater = getMenuInflater();

inflater.inflate(R.menu.context_menu, menu);

}

• In order for a View to provide a context menu, you must "register" the view for a context menu Call registerForContextMenu() and pass it the View you want to give a context menu When this View then receives a long-press, it displays a context menu.

• If your activity uses a ListView and you want all list items to provide a context menu, register all items for a context menu by passing the ListView to

registerForContextMenu() For example, if you're using a ListActivity , at the very end of the onCreate() method add this line:

• registerForContextMenu ( getListView() );

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Handling options menu selections

@Override

public boolean onOptionsItemSelected(MenuItem item) { // Handle item selection

switch (item.getItemId()) { case R.id.new_game:

newGame();

return true; case R.id.help:

showHelp();

return true; default:

return super.onOptionsItemSelected(item);

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Handling context menu selections

@Override

public boolean onContextItemSelected(MenuItem item) { AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();

switch (item.getItemId()) { case R.id.edit:

editNote(info.id);

return true; case R.id.delete:

deleteNote(info.id);

return true; default:

return super.onContextItemSelected(item);

}

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Handling checkable menu items

@Override

public boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) {

case R.id.vibrate:

case R.id.dont_vibrate:

if (item.isChecked()) item.setChecked(false);

else

item.setChecked(true);

return true;

default: return super.onOptionsItemSelected(item);

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or ContextItem

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Creating menus by using code

static final private int MENU_ITEM = Menu FIRST;

// Unique menu item identifier Used for event handling.

int menuItemId = MENU_ITEM;

// The order position of the item

int menuItemOrder = Menu NONE;

// Text to be displayed for this menu item.

int menuItemText = R string.menu_item;

// Create the menu item and keep a reference to it.

menuItemOrder, menuItemText);

return true;

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Creating menus by using code

// Create a new check box item.

menu.add(0, CHECKBOX_ITEM, Menu NONE, " CheckBox" ).setCheckable(true);

// Create a radio button group.

menu.add(RB_GROUP, RADIOBUTTON_1, Menu NONE, "Radiobutton 1" );

menu.add(RB_GROUP, RADIOBUTTON_2, Menu NONE, "Radiobutton 2" );

menu.add(RB_GROUP, RADIOBUTTON_3, Menu NONE,

"Radiobutton 3" ).setChecked( true );

menu.setGroupCheckable(RB_GROUP, true, true);

// Add a shortcut to this menu item, ‘0’ if using the numeric keypad // or ‘b’ if using the full keyboard.

menuItem.setShortcut( '0' , 'b' );

// or

menuItem.setNumericShortcut( '0' );

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