Android View

8/12/2019 Android View

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1Android BUAP - FCC MALCH

Android View

Dr. Miguel Angel Len Chvez


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Android big picture

! View Views are user interface (UI) elements that form the

basic building blocks of a user interface. Views are

hierarchical and they know how to draw themselves. Aview could be a button, label, text field, or other UIs.

! Activities The building block of the user interface is the activity.

! Content Providers They provide a level of abstraction for any data stored

on one deve that is accessible by multiple applications.


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Android big picture

! Intents Intents are system messages, running around the inside

of the device, notifying applications of various events,

from hardware state changes to incoming data toapplication events

! Services Activities, content providers, and intent receivers are all

short-lived and can be shut down at any time. Services,on the other hand, are designed to keep running, if

needed, independent of any activity.


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User interface

! The graphical user interface for an Android app isbuilt using a hierarchy of View and ViewGroup

objects.

! View objects are usually UI widgets such asbuttons or text fields

! ViewGroup objects are invisible view containersthat define how the child views are laid out, such

as in a grid or a vertical list


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UI


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UI

! Android provides an XML vocabulary thatcorresponds to the subclasses of View and

ViewGroup so you can define your UI in XML

using a hierarchy of UI elements.


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UI


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UI

! LinearLayout is a view group (a subclass ofViewGroup) that lays out child views in either a

vertical or horizontal orientation, as specified by the

android:orientation attribute.! Each child of a LinearLayout appears on the screen in

the order in which it appears in the XML.

! Because the LinearLayout is the root view in thelayout, it should fill the entire screen area that'savailable to the app by setting the width and height to

"match_parent".


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Add a text field


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android:id

! Unique identifier for the view, to reference the object fromyour app code, such as to read and manipulate the object.

! The at sign (@) is required for referring to any resourceobject from XML. It is followed by the resource type (idin this case), a slash, then the resource name(edit_message).

! The plus sign (+) before the resource type is needed onlywhen you're defining a resource ID for the first time.When you compile the app, the SDK tools use the ID

name to create a new resource ID in your project's gen/R.java file that refers to the EditText element.


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Add a text field

! wrap_content This value specifies that the view should be only as big

as needed to fit the contents of the view.

! android:hint This is a default string to display when the text field is

empty.


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Add string resources

My First AppEnter a messageSendSettingsMainActivity


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Add string resources

! String resources allow you to manage all UI textin a single location, which makes it easier to find

and update text.

! By default, your Android project includes a stringresource file at res/values/strings.xml.


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Add a button


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Respond to the Send Button


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Respond to the Send Button

! MainActivity classimport android.view.View;

/** Called when the user clicks the Send button */

public void sendMessage(View view) {

// Do something in response to button

}


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Build an Intent

! An Intent is an object that provides runtime binding betweenseparate components (such as two activities).

! The Intent represents an apps "intent to do something.! An intent not only allows you to start another activity, but it

can carry a bundle of data to the activity as well.

Inside the sendMessage() method:

Intent intent = new Intent(this, DisplayMessageActivity.class);

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


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Start the Second Activity

/** Called when the user clicks the Send button */public void sendMessage(View view) {

Intent intent = new Intent(this,

DisplayMessageActivity.class);EditText editText = (EditText)findViewById(R.id.edit_message);String message = editText.getText().toString();intent.putExtra(EXTRA_MESSAGE, message);startActivity(intent);

}


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Create the Second Activity

public class DisplayMessageActivity extends Activity {

@SuppressLint("NewApi")

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_display_message);

// Make sure we're running on Honeycomb or higher to use ActionBar APIsif (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {

// Show the Up button in the action bar.

getActionBar().setDisplayHomeAsUpEnabled(true);

}

}

@Override

public boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) {case android.R.id.home:

NavUtils.navigateUpFromSameTask(this);

return true;

}

return super.onOptionsItemSelected(item);

}

}


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Add it to the manifest

...


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Receive the Intent

! In the DisplayMessageActivity classs onCreate()method

Intent intent = getIntent();

String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);


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Display the Message

@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);

// Get the message from the intent

Intent intent = getIntent();

String message =intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

// Create the text view

TextView textView = new TextView(this);

textView.setTextSize(40);

textView.setText(message);

// Set the text view as the activity layout

setContentView(textView);

}


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Android App


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Referencias

! Android Developer Website: The Android SDK and developerreference site: http://developer.android.com/

! http://developer.android.com/training/basics/firstapp/starting-activity.html#StartActivity

Documents

Android View