Building your first app

Better reference the original webpage httpdeveloperandroidcomtrainingbasicsfirstappindexhtml

Download the Android SDK httpdeveloperandroidcomsdkindexhtml

Install the ADT plugin for Eclipse (if yoursquoll use the Eclipse IDE)

Eclipse download httpeclipseorgmobile

Basic Requirements

ADT plugin downlaod Start Eclipse then select Help gt Install New Software Click Add in the top-right corner In the Add Repository dialog that appears enter ADT Plugin for

the Name and the following URL for the Locationhttpsdl-sslgooglecomandroideclipse

Click OKIf you have trouble acquiring the plugin try using http in the Location URL instead of https (https is preferred for security reasons)

In the Available Software dialog select the checkbox next to Developer Tools and click Next

In the next window youll see a list of the tools to be downloaded Click Next

Read and accept the license agreements then click FinishIf you get a security warning saying that the authenticity or validity of the software cant be established click OK

When the installation completes restart Eclipse

Basic Requirements(contrsquod)

Download the latest SDK tools and platforms using the SDK Manager

Basic Requirements(contrsquod)

Click New in the toolbarIn the window that appears open

the Android folder select Android Application Project and click Next

Fill in the form that appearsApplication Name Project Name Package NameMinimum Required SDK Target SDK Compile With Theme then click Nextselect BlankActivity and click Nextclick Finish

Create an Android project

AndroidManifestxml have ltuses-sdkgt element

src have includes an Activity class

res have app resources with is something like

drawable-hdpi layout values

Important checking

Download the latest SDK tools and platforms using the SDK Manager

Basic Requirements(contrsquod)

Click New in the toolbarIn the window that appears open

the Android folder select Android Application Project and click Next

Fill in the form that appearsApplication Name Project Name Package NameMinimum Required SDK Target SDK Compile With Theme then click Nextselect BlankActivity and click Nextclick Finish

Create an Android project

AndroidManifestxml have ltuses-sdkgt element

src have includes an Activity class

res have app resources with is something like

drawable-hdpi layout values

Important checking

Click New in the toolbarIn the window that appears open

the Android folder select Android Application Project and click Next

Fill in the form that appearsApplication Name Project Name Package NameMinimum Required SDK Target SDK Compile With Theme then click Nextselect BlankActivity and click Nextclick Finish

Create an Android project

AndroidManifestxml have ltuses-sdkgt element

src have includes an Activity class

res have app resources with is something like

drawable-hdpi layout values

Important checking

AndroidManifestxml have ltuses-sdkgt element

src have includes an Activity class

res have app resources with is something like

drawable-hdpi layout values

Important checking

Plug in your device to your development machine with a USB cable(install the appropriate USB driver for your device if needed)

Enable USB debugging on your device(On Android 40 and newer its in Settings gt Developer options)

Run in Eclipse1click Run from the toolbar2 In the Run as window that appears

select Android Application and click OK

Run on a Real Device

Launch the Android Virtual Device ManagerIn Eclipse click Android Virtual Device Manager from the toolbar

In the Android Virtual Device Manager panel click New

Fill in the details for the AVD Click Create AVDSelect the new AVD from the Android Virtual

Device Manager and click StartAfter the emulator boots up unlock the

emulator screen

Run on emulator

Run in Eclipse1click Run from the toolbar2 In the Run as window that appears

select Android Application and click OK

Run on emulator(contrsquod)

The graphical user interface for an Android app is built using a hierarchy of View and ViewGroup objects

View objects are usually UI widgets such as buttons or text fields

ViewGroup objects are invisible view containers that define how the child views are laid out such as in a grid or a vertical list

Building a Simple User Interface

Launch the Android Virtual Device ManagerIn Eclipse click Android Virtual Device Manager from the toolbar

In the Android Virtual Device Manager panel click New

Fill in the details for the AVD Click Create AVDSelect the new AVD from the Android Virtual

Device Manager and click StartAfter the emulator boots up unlock the

emulator screen

Run on emulator

Run in Eclipse1click Run from the toolbar2 In the Run as window that appears

select Android Application and click OK

Run on emulator(contrsquod)

The graphical user interface for an Android app is built using a hierarchy of View and ViewGroup objects

View objects are usually UI widgets such as buttons or text fields

ViewGroup objects are invisible view containers that define how the child views are laid out such as in a grid or a vertical list

Building a Simple User Interface

Run in Eclipse1click Run from the toolbar2 In the Run as window that appears

select Android Application and click OK

Run on emulator(contrsquod)

The graphical user interface for an Android app is built using a hierarchy of View and ViewGroup objects

View objects are usually UI widgets such as buttons or text fields

ViewGroup objects are invisible view containers that define how the child views are laid out such as in a grid or a vertical list

Building a Simple User Interface

The graphical user interface for an Android app is built using a hierarchy of View and ViewGroup objects

View objects are usually UI widgets such as buttons or text fields

ViewGroup objects are invisible view containers that define how the child views are laid out such as in a grid or a vertical list

Building a Simple User Interface

Open the activity_mainxml file from the reslayout directoryFirst delete the ltTextViewgt element and change the lt

RelativeLayoutgt element to ltLinearLayoutgt Then add the androidorientation attribute and set it to horizontal

Add a Text Field-To create a user-editable text field add an ltEditTextgt element inside the ltLinearLayoutgt The result looks like this

ltxml version=10 encoding=utf-8gtltLinearLayout xmlnsandroid=httpschemasandroidcomapkresandroid xmlnstools=httpschemasandroidcomtools androidlayout_width=match_parent androidlayout_height=match_parent androidorientation=horizontal gtltLinearLayoutgt

Create a Linear Layout

To create a user-editable text field add an ltEditTextgt element inside the ltLinearLayoutgt

Add a Text Field

By default your Android project includes a string resource file at resvaluesstringsxml Add a new string named edit_message and set the value to Enter a messageldquo

While yoursquore in this file also add a Send string for the button yoursquoll soon add called button_send

The result for stringsxml looks like thisltxml version=10 encoding=utf-8gt

ltresourcesgt ltstring name=app_namegtMy First Appltstringgt ltstring name=edit_messagegtEnter a messageltstringgt ltstring name=button_sendgtSendltstringgt ltstring name=menu_settingsgtSettingsltstringgt ltstring name=title_activity_maingtMainActivityltstringgtltresourcesgt

Add String Resources

Now add a ltButtongt to the layout immediately following the ltEditTextgt element

ltButton androidlayout_width=wrap_content androidlayout_height=wrap_content androidtext=stringbutton_send gt

The height and width are set to wrap_content so the button is only as big as necessary to fit the buttons text This button doesnt need the androidid attribute because it wont be referenced from the activity code

Add a Button

Now add a ltButtongt to the layout immediately following the ltEditTextgt element

ltButton androidlayout_width=wrap_content androidlayout_height=wrap_content androidtext=stringbutton_send gt

The height and width are set to wrap_content so the button is only as big as necessary to fit the buttons text This button doesnt need the androidid attribute because it wont be referenced from the activity code

Add a Button

Respond to the Send ButtonTo respond to the buttons on-click event open

theactivity_mainxml layout file and add theandroidonClick attribute to the ltButtongt element

ltButton androidlayout_width=wrap_content androidlayout_height=wrap_content androidtext=stringbutton_send androidonClick=sendMessage gt

The androidonClick attributersquos value sendMessage is the name of a method in your activity that the system calls when the user clicks the button

Starting Another Activity

Intent represents an apprsquos intent to do something You can use intents for a wide variety of tasks but most often theyrsquore used to start another activity

Inside the sendMessage() method create an Intent to start an activity called DisplayMessageActivity

Intent intent = new Intent(this DisplayMessageActivityclass)

Build an Intent

The constructor used here takes two parameters

A Context as its first parameter (this is used because the Activity class is a subclass of Context)

The Class of the app component to which the system should deliver the Intent (in this case the activity that should be started)

Build an Intent(contrsquod)

An intent not only allows you to start another activity but it can carry a bundle of data to the activity as well Inside thesendMessage() method use findViewById() to get theEditText element and add its text value to the intent

Intent intent = new Intent(this DisplayMessageActivityclass)EditText editText = (EditText) findViewById(Ridedit_message)String message = editTextgetText()toString()intentputExtra(EXTRA_MESSAGE message)

Build an Intent(contrsquod)

To start an activity call startActivity() and pass it your Intent The system receives this call and starts an instance of the Activity specified by the Intent

With this new code the complete sendMessage() method thats invoked by the Send button now looks like this

Called when the user clicks the Send button public void sendMessage(View view) Intent intent = new Intent(this DisplayMessageActivityclass) EditText editText = (EditText) findViewById(Ridedit_message) String message = editTextgetText()toString() intentputExtra(EXTRA_MESSAGE message) startActivity(intent)

Now you need to create the DisplayMessageActivity class in order for this to work

Start the Second Activity

Click New in the toolbarIn the window that appears open theAndroid folder

and select Android Activity Click NextSelect BlankActivity and click NextFill in the activity detailsProject MyFirstAppActivity Name DisplayMessageActivityLayout Name activity_display_messageTitle My MessageHierarchial Parent

comexamplemyfirstappMainActivityNavigation Type NoneClick Finish

Create the Second Activity

Every Activity is invoked by an Intent regardless of how the user navigated there You can get the Intentthat started your activity by calling getIntent() and retrieve the data contained within it

In the DisplayMessageActivity classrsquos onCreate() method get the intent and extract the message delivered by MainActivity

Intent intent = getIntent()String message = intentgetStringExtra(MainActivityEXTRA_MESSAGE)

Receive the Intent

Every Activity is invoked by an Intent regardless of how the user navigated there You can get the Intentthat started your activity by calling getIntent() and retrieve the data contained within it

In the DisplayMessageActivity classrsquos onCreate() method get the intent and extract the message delivered by MainActivity

Intent intent = getIntent()String message = intentgetStringExtra(MainActivityEXTRA_MESSAGE)

Receive the Intent

To show the message on the screen create a TextView widget and set the text using setText() Then add theTextView as the root view of the activityrsquos layout by passing it to setContentView()

The complete onCreate() method for DisplayMessageActivity now looks like this Override

public void onCreate(Bundle savedInstanceState) superonCreate(savedInstanceState)

Get the message from the intent Intent intent = getIntent() String message = intentgetStringExtra(MainActivityEXTRA_MESSAGE)

Create the text view TextView textView = new TextView(this) textViewsetTextSize(40) textViewsetText(message)

Set the text view as the activity layout setContentView(textView)

Display the Message

Better reference the original webpage if any question

END

• Building your first app
• Basic Requirements
• Basic Requirements(contrsquod)
• Basic Requirements(contrsquod)
• Create an Android project
• Important checking
• Run on a Real Device
• Run on emulator
• Run on emulator(contrsquod)
• Building a Simple User Interface
• Create a Linear Layout
• Add a Text Field
• Add String Resources
• Add a Button
• Starting Another Activity
• Build an Intent
• Build an Intent(contrsquod)
• Build an Intent(contrsquod) (2)
• Start the Second Activity
• Create the Second Activity
• Receive the Intent
• Display the Message
• END