Android (MC)

1.  
Explain
Android platform architecture.OR

          What Is Android. Explain Android
Software Stack.




Android Architecture

android architecture or Android software stack is
categorized into five parts:

linux kernel
native libraries (middleware),
Android Runtime
Application Framework
Applications


Let's see the android
architecture first.

6.   
 




1) Linux kernel

It is the heart of android architecture that exists at the root of
android architecture. Linux kernel is
responsible for device drivers, power management, memory management, device
management and resource access.






2) Native Libraries

On the top of linux kernel, their are Native
libraries such as WebKit, OpenGL, FreeType, SQLite, Media, C runtime
library (libc) etc.

The WebKit library is responsible for browser support, SQLite is
for database, FreeType for font support, Media for playing and recording audio
and video formats.






3) Android Runtime

In android runtime, there are core libraries and DVM (Dalvik
Virtual Machine) which is responsible to run android application. DVM is like
JVM but it is optimized for mobile devices. It consumes less memory and
provides fast performance.






4) Android Framework

On the top of Native libraries and android runtime, there is
android framework. Android framework includes Android
API's such as UI (User Interface), telephony, resources,
locations, Content Providers (data) and package managers. It provides a lot of
classes and interfaces for android application development.






5) Applications

On the top of android framework, there are applications. All
applications such as home, contact, settings, games, browsers are using android
framework that uses android runtime and libraries. Android runtime and native
libraries are using linux kernal.




2.
 List and describe in detail Android
development tools

The android developer tools let you create interactive and
powerful application for android platform. The tools can be generally
categorized into two types.

·      SDK tools

·      Platform
tools

SDK tools

SDK tools are generally platform independent and are required no
matter which android platform you are working on. When you install the Android
SDK into your system, these tools get automatically installed. The list of SDK
tools has been given below −

 


  

  

Sr.No

  

  

Tool & description

 

  

  

1

  

  

android

This tool lets you manage AVDs,
  projects, and the installed components of the SDK

 

  

  

2

  

  

ddms

This tool lets you debug
  Android applications

 

  

  

3

  

  

Draw 9-Patch

This tool allows you to easily
  create a NinePatch graphic using a WYSIWYG editor

 

  

  

4

  

  

emulator

This tools let you test your
  applications without using a physical device

 

  

  

5

  

  

mksdcard

Helps you create a disk image
  (external sdcard storage) that you can use with the emulator

 

  

  

6

  

  

proguard

Shrinks, optimizes, and
  obfuscates your code by removing unused code

 

  

  

7

  

  

sqlite3

Lets you access the SQLite data
  files created and used by Android applications

 

  

  

8

  

  

traceview

Provides a graphical viewer for
  execution logs saved by your application

 

  

  

9

  

  

Adb

Android Debug Bridge (adb) is a
  versatile command line tool that lets you communicate with an emulator
  instance or connected Android-powered device.

 


We will discuss three important tools here that are android,ddms
and sqlite3.

Android

Android is a development tool that lets you perform these tasks:

·      Manage
Android Virtual Devices (AVD)

·      Create
and update Android projects

·      Update
your sdk with new platform add-ons and documentation

android [global options] action [action options]


DDMS

DDMS stands for Dalvik debug monitor server, that provide many
services on the device. The service could include message formation, call
spoofing, capturing screenshot, exploring internal threads and file systems
e.t.c

Running DDMS

From Android studio click on Tools>Android>Android
device Monitor.

How it works

In android, each application runs in its own process and each
process run in the virtual machine. Each VM exposes a unique port, that a
debugger can attach to.

When DDMS starts, it connects to adb. When a device is connected,
a VM monitoring service is created between adb and DDMS, which notifies DDMS
when a VM on the device is started or terminated.

Making SMS

Making sms to emulator.we need to call telnet client and server as
shown below



Now click on send button, and you will see an sms notification in
the emulator window. It is shown below −



Making Call

In the DDMS, select the Emulator Control tab. In the emulator
control tab , click on voice and then start typing the incoming number. It is
shown in the picture below −



Now click on the call button to make a call to your emulator. It
is shown below −



Now click on hangup in the Android studio window to terminate the
call.

The fake sms and call can be viewed from the notification by just
dragging the notification window to the center using mouse. It is shown below −



Capturing ScreenShot

You can also capture screenshot of your emulator. For this look
for the camera icon on the right side under Devices tab. Just point your mouse
over it and select it.

As soon as you select it , it will start the screen capturing
process and will capture whatever screen of the emulator currently active. It
is shown below −



The eclipse orientation can be changed using Ctrl + F11 key. Now
you can save the image or rotate it and then select done to exit the screen
capture dialog.

Sqlite3

Sqlite3 is a command line program which is used to manage the
SQLite databases created by Android applications. The tool also allow us to
execute the SQL statements on the fly.

There are two way through which you can use SQlite , either from
remote shell or you can use locally.

Use Sqlite3 from a remote shell.

Enter a remote shell by entering the following command −

adb [-d|-e|-s {<serialNumber>}] shell


From a remote shell, start the sqlite3 tool by entering the
following command −

sqlite3


Once you invoke sqlite3, you can issue sqlite3 commands in the
shell. To exit and return to the adb remote shell, enter exit or press CTRL+D.

Using Sqlite3 directly

Copy a database file from your device to your host machine.

adb pull <database-file-on-device>


Start the sqlite3 tool from the /tools directory, specifying the
database file −

sqlite3 <database-file-on-host>


Platform tools

The platform tools are customized to support the features of the
latest android platform.

The platform tools are typically updated every time you install a
new SDK platform. Each update of the platform tools is backward compatible with
older platforms.

Some of the platform tools are listd below −

·      Android
Debug bridge (ADB)

·      Android
Interface definition language (AIDL)

·      aapt,
dexdump , and dex e.t.c




3.  
Explain the lifecycle of Android Activity    OR

Explain Activity
Life-Cycle in android by giving a suitable      
example.






 

Android Activity Lifecycle







Android Activity Lifecycle is
controlled by 7 methods of android.app.Activity class. The android Activity is
the subclass of ContextThemeWrapper class.

An activity is the single screen in android. It is like window or
frame of Java.

By the help of activity, you can place all your UI components or
widgets in a single screen.

The 7 lifecycle method of Activity describes how activity will
behave at different states.

Android Activity Lifecycle methods

Let's see the 7 lifecycle methods of android activity.

 


  

  

Method

  

  

Description

 

  

  

onCreate

  

  

called
  when activity is first created.

 

  

  

onStart

  

  

called
  when activity is becoming visible to the user.

 

  

  

onResume

  

  

called
  when activity will start interacting with the user.

 

  

  

onPause

  

  

called
  when activity is not visible to the user.

 

  

  

onStop

  

  

called
  when activity is no longer visible to the user.

 

  

  

onRestart

  

  

called
  after your activity is stopped, prior to start.

 

  

  

onDestroy

  

  

called
  before the activity is destroyed.

 


 

File: activity_main.xml

1.   
<?xml version="1.0" encoding="utf-8"?>  

2.   
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"  

3.   
    xmlns:app="http://schemas.android.com/apk/res-auto"  

4.   
    xmlns:tools="http://schemas.android.com/tools"  

5.   
    android:layout_width="match_parent"  

6.   
    android:layout_height="match_parent"  

7.   
    tools:context="example.javatpoint.com.activitylifecycle.MainActivity">  

8.   
  

9.   
    <TextView  

10.         android:layout_width="wrap_content"  

11.         android:layout_height="wrap_content"  

12.         android:text="Hello World!"  

13.         app:layout_constraintBottom_toBottomOf="parent"  

14.         app:layout_constraintLeft_toLeftOf="parent"  

15.         app:layout_constraintRight_toRightOf="parent"  

16.         app:layout_constraintTop_toTopOf="parent" />  

17.   

18. </android.support.constraint.ConstraintLayout>  

Android Activity Lifecycle
Example

It provides the details about the invocation of life cycle methods
of activity. In this example, we are displaying the content on the logcat.

File:
MainActivity.java

1.   
package example.javatpoint.com.activitylifecycle;  

2.   
  

3.   
import android.app.Activity;  

4.   
import android.os.Bundle;  

5.   
import android.util.Log;  

6.   
  

7.   
public class MainActivity extends Activity {  

8.   
  

9.   
    @Override  

10.     protected void onCreate(Bundle savedInstanceState) {  

11.         super.onCreate(savedInstanceState);  

12.         setContentView(R.layout.activity_main);  

13.         Log.d("lifecycle","onCreate invoked");  

14.     }  

15.     @Override  

16.     protected void onStart() {  

17.         super.onStart();  

18.         Log.d("lifecycle","onStart invoked");  

19.     }  

20.     @Override  

21.     protected void onResume() {  

22.         super.onResume();  

23.         Log.d("lifecycle","onResume invoked");  

24.     }  

25.     @Override  

26.     protected void onPause() {  

27.         super.onPause();  

28.         Log.d("lifecycle","onPause invoked");  

29.     }  

30.     @Override  

31.     protected void onStop() {  

32.         super.onStop();  

33.         Log.d("lifecycle","onStop invoked");  

34.     }  

35.     @Override  

36.     protected void onRestart() {  

37.         super.onRestart();  

38.         Log.d("lifecycle","onRestart invoked");  

39.     }  

40.     @Override  

41.     protected void onDestroy() {  

42.         super.onDestroy();  

43.         Log.d("lifecycle","onDestroy invoked");  

44.     }  

45. }  




4.
Write
detailed note on different types of layouts

Android Layout Types

There are number of Layouts provided by Android which you will use
in almost all the Android applications to provide different view, look and
feel.

 


  

  

Sr.No

  

  

Layout & Description

 

  

  

1

  

  

Linear Layout

LinearLayout is a view group
  that aligns all children in a single direction, vertically or horizontally.

 

  

  

2

  

  

Relative Layout

RelativeLayout is a view group
  that displays child views in relative positions.

 

  

  

3

  

  

Table Layout

TableLayout is a view that
  groups views into rows and columns.

 

  

  

4

  

  

Absolute Layout

AbsoluteLayout enables you to
  specify the exact location of its children.

 

  

  

5

  

  

Frame Layout

The FrameLayout is a
  placeholder on screen that you can use to display a single view.

 

  

  

6

  

  

List View

ListView is a view group that
  displays a list of scrollable items.

 

  

  

7

  

  

Grid View

GridView is a ViewGroup that
  displays items in a two-dimensional, scrollable grid.

 

  

  




  

  




 








Android
LinearLayout is a view group that aligns all children in either vertically or horizontally.



LINEAR LAYOUT

LinearLayout Attributes

Following are the important attributes specific to LinearLayout −

 


  

  

Sr.No

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:baselineAligned

This must be a boolean value,
  either "true" or "false" and prevents the layout from
  aligning its children's baselines.

 

  

  

3

  

  

android:baselineAlignedChildIndex

When a linear layout is part of
  another layout that is baseline aligned, it can specify which of its children
  to baseline align.

 

  

  

4

  

  

android:divider

This is drawable to use as a
  vertical divider between buttons. You use a color value, in the form of
  "#rgb", "#argb", "#rrggbb", or
  "#aarrggbb".

 

  

  

5

  

  

android:gravity

This specifies how an object
  should position its content, on both the X and Y axes. Possible values are
  top, bottom, left, right, center, center_vertical, center_horizontal etc.

 

  

  

6

  

  

android:orientation

This specifies the direction of
  arrangement and you will use "horizontal" for a row,
  "vertical" for a column. The default is horizontal.

 

  

  

7

  

  

android:weightSum

Sum up of child weight

 


Following is the content of
the modified main activity file src/com.example.demo/MainActivity.java.
This file can include each of the fundamental lifecycle methods.



package com.example.demo;




import android.os.Bundle;

import android.app.Activity;




public class MainActivity
extends Activity
{

   @Override

   protected void
onCreate(Bundle
savedInstanceState) {

     
super.onCreate(savedInstanceState);

     
setContentView(R.layout.activity_main);

   }

}


Following will be the
content of res/layout/activity_main.xml file −



<?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" >

   

   <Button android:id="@+id/btnStartService"

     
android:layout_width="270dp"

     
android:layout_height="wrap_content"

     
android:text="start_service"/>

     


   <Button android:id="@+id/btnPauseService"

     
android:layout_width="270dp"

     
android:layout_height="wrap_content"

     
android:text="pause_service"/>

     


   <Button android:id="@+id/btnStopService"

     
android:layout_width="270dp"

     
android:layout_height="wrap_content"

     
android:text="stop_service"/>

     


</LinearLayout>


Following will be the
content of res/values/strings.xml to define two new constants
−



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

<resources>

   <string name="app_name">HelloWorld</string>

   <string name="action_settings">Settings</string>

</resources>


RELATIVE LAYOUT




Android
RelativeLayout enables you to specify how child views are positioned relative
to each other. The position of each view can be specified as relative to
sibling elements or relative to the parent.



RELATIVE LAYOUT

RelativeLayout
Attributes

Following are the important attributes specific to RelativeLayout
−

 


  

  

Sr.No.

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:gravity

This specifies how an object
  should position its content, on both the X and Y axes. Possible values are
  top, bottom, left, right, center, center_vertical, center_horizontal etc.

 

  

  

3

  

  

android:ignoreGravity

This indicates what view should
  not be affected by gravity.

 


Using RelativeLayout, you can align two elements by right border,
or make one below another, centered in the screen, centered left, and so on. By
default, all child views are drawn at the top-left of the layout, so you must
define the position of each view using the various layout properties available
from RelativeLayout.LayoutParams and few of the important
attributes are given below −

 


  

  

Sr.No.

  

  

Attribute & Description

 

  

  

1

  

  

android:layout_above

Positions the bottom edge of
  this view above the given anchor view ID and must be a reference to another
  resource, in the form "@[+][package:]type:name"

 

  

  

2

  

  

android:layout_alignBottom

Makes the bottom edge of this
  view match the bottom edge of the given anchor view ID and must be a
  reference to another resource, in the form
  "@[+][package:]type:name".

 

  

  

3

  

  

android:layout_alignLeft

Makes the left edge of this
  view match the left edge of the given anchor view ID and must be a reference
  to another resource, in the form "@[+][package:]type:name".

 

  

  

4

  

  

android:layout_alignParentBottom

If true, makes the bottom edge
  of this view match the bottom edge of the parent. Must be a boolean value,
  either "true" or "false".

 

  

  

5

  

  

android:layout_alignParentEnd

If true, makes the end edge of
  this view match the end edge of the parent. Must be a boolean value, either
  "true" or "false".

 

  

  

6

  

  

android:layout_alignParentLeft

If true, makes the left edge of
  this view match the left edge of the parent. Must be a boolean value, either
  "true" or "false".

 

  

  

7

  

  

android:layout_alignParentRight

If true, makes the right edge
  of this view match the right edge of the parent. Must be a boolean value,
  either "true" or "false".

 

  

  

8

  

  

android:layout_alignParentStart

If true, makes the start edge
  of this view match the start edge of the parent. Must be a boolean value,
  either "true" or "false".

 

  

  

9

  

  

android:layout_alignParentTop

If true, makes the top edge of
  this view match the top edge of the parent. Must be a boolean value, either
  "true" or "false".

 

  

  

10

  

  

android:layout_alignRight

Makes the right edge of this
  view match the right edge of the given anchor view ID and must be a reference
  to another resource, in the form "@[+][package:]type:name".

 

  

  

11

  

  

android:layout_alignStart

Makes the start edge of this
  view match the start edge of the given anchor view ID and must be a reference
  to another resource, in the form "@[+][package:]type:name".

 

  

  

12

  

  

android:layout_alignTop

Makes the top edge of this view
  match the top edge of the given anchor view ID and must be a reference to
  another resource, in the form "@[+][package:]type:name".

 

  

  

13

  

  

android:layout_below

Positions the top edge of this
  view below the given anchor view ID and must be a reference to another
  resource, in the form "@[+][package:]type:name".

 

  

  

14

  

  

android:layout_centerHorizontal

If true, centers this child
  horizontally within its parent. Must be a boolean value, either "true"
  or "false".

 

  

  

15

  

  

android:layout_centerInParent

If true, centers this child
  horizontally and vertically within its parent. Must be a boolean value,
  either "true" or "false".

 

  

  

16

  

  

android:layout_centerVertical

If true, centers this child
  vertically within its parent. Must be a boolean value, either
  "true" or "false".

 

  

  

17

  

  

android:layout_toEndOf

Positions the start edge of
  this view to the end of the given anchor view ID and must be a reference to
  another resource, in the form "@[+][package:]type:name".

 

  

  

18

  

  

android:layout_toLeftOf

Positions the right edge of
  this view to the left of the given anchor view ID and must be a reference to
  another resource, in the form "@[+][package:]type:name".

 

  

  

19

  

  

android:layout_toRightOf

Positions the left edge of this
  view to the right of the given anchor view ID and must be a reference to
  another resource, in the form "@[+][package:]type:name".

 

  

  

20

  

  

android:layout_toStartOf

Positions the end edge of this
  view to the start of the given anchor view ID and must be a reference to
  another resource, in the form "@[+][package:]type:name".

 





Following is the content of the modified main activity
file src/com.example.demo/MainActivity.java. This file can include
each of the fundamental lifecycle methods.



package com.example.demo;




import android.os.Bundle;

import android.app.Activity;




public class MainActivity
extends Activity {

   @Override

   protected void onCreate(Bundle
savedInstanceState) {

      super.onCreate(savedInstanceState);

      setContentView(R.layout.activity_main);

   }

   

}


Following will be the content of res/layout/activity_main.xml file
−



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

   android:layout_width="fill_parent"

  
android:layout_height="fill_parent"

   android:paddingLeft="16dp"

   android:paddingRight="16dp" >

   

   <EditText

      android:id="@+id/name"

     
android:layout_width="fill_parent"

     
android:layout_height="wrap_content"

      android:hint="@string/reminder"
/>

      

   <LinearLayout

      android:orientation="vertical"

     
android:layout_width="fill_parent"

     
android:layout_height="fill_parent"

     
android:layout_alignParentStart="true"

     
android:layout_below="@+id/name">

      

      <Button

        
android:layout_width="wrap_content"

        
android:layout_height="wrap_content"

         android:text="New Button"

         android:id="@+id/button"
/>

      

      <Button

        
android:layout_width="wrap_content"

         android:layout_height="wrap_content"

         android:text="New Button"

         android:id="@+id/button2"
/>

      

   </LinearLayout>




</RelativeLayout>


Following will be the content of res/values/strings.xml to
define two new constants −



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

<resources>

   <string
name="action_settings">Settings</string>

   <string
name="reminder">Enter your name</string>

</resources>


Let's try to run our modified Hello World! application
we just modified. I assume you had created your AVD while
doing environment setup. To run the app from Android Studio, open one of your
project's activity files and click Run  icon
from the toolbar. Android Studio installs the app on your AVD and starts it and
if everything is fine with your setup and application, it will display
following Emulator window −



TableLayout

Android
TableLayout going to be arranged groups of views into rows and columns. You
will use the <TableRow> element to build a row in the table. Each row has
zero or more cells; each cell can hold one View object.

TableLayout containers do not display border lines for their rows,
columns, or cells.



TableLayout Attributes

Following are the important attributes specific to TableLayout −

 


  

  

Sr.No.

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:collapseColumns

This specifies the zero-based
  index of the columns to collapse. The column indices must be separated by a
  comma: 1, 2, 5.

 

  

  

3

  

  

android:shrinkColumns

The zero-based index of the
  columns to shrink. The column indices must be separated by a comma: 1, 2, 5.

 

  

  

4

  

  

android:stretchColumns

The zero-based index of the
  columns to stretch. The column indices must be separated by a comma: 1, 2, 5.

 


 

 

ABSOLUTE LAYOUT




An
Absolute Layout lets you specify exact locations (x/y coordinates) of its
children. Absolute layouts are less flexible and harder to maintain than other
types of layouts without absolute positioning.



ABSOLUTE LAYOUT

AbsoluteLayout
Attributes

Following are the important attributes specific to AbsoluteLayout
−

 


  

  

Sr.No

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:layout_x

This specifies the x-coordinate
  of the view.

 

  

  

3

  

  

android:layout_y

This specifies the y-coordinate
  of the view.

 


Public Constructors

 


  

  

AbsoluteLayout(Context
  context)

 

  

  

AbsoluteLayout(Context
  context, AttributeSet attrs)

 

  

  

AbsoluteLayout(Context
  context, AttributeSet attrs, int defStyleAttr)

 

  

  

AbsoluteLayout(Context
  context, AttributeSet attrs, int defStyleAttr, int defStyleRes)

 





FRAME LAYOUT




Frame
Layout is designed to block out an area on the screen to display a single item.
Generally, FrameLayout should be used to hold a single child view, because it
can be difficult to organize child views in a way that's scalable to different
screen sizes without the children overlapping each other.

You can, however, add multiple children to a FrameLayout and control
their position within the FrameLayout by assigning gravity to each child, using
the android:layout_gravity attribute.



FRAME LAYOUT




FrameLayout Attributes

Following are the important attributes specific to FrameLayout −

 


  

  

Sr.No

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:foreground

This defines the drawable to
  draw over the content and possible values may be a color value, in the form
  of "#rgb", "#argb", "#rrggbb", or
  "#aarrggbb".

 

  

  

3

  

  

android:foregroundGravity

Defines the gravity to apply to
  the foreground drawable. The gravity defaults to fill. Possible values are
  top, bottom, left, right, center, center_vertical, center_horizontal etc.

 

  

  

4

  

  

android:measureAllChildren

Determines whether to measure
  all children or just those in the VISIBLE or INVISIBLE state when measuring.
  Defaults to false.

 





ListView

Android ListView is
a view which groups several items and display them in vertical scrollable list.
The list items are automatically inserted to the list using an Adapter that
pulls content from a source such as an array or database.



LIST VIEW

An adapter actually bridges between UI components and the data
source that fill data into UI Component. Adapter holds the data and send the
data to adapter view, the view can takes the data from adapter view and shows
the data on different views like as spinner, list view, grid view etc.

The ListView and GridView are
subclasses of AdapterView and they can be populated by binding
them to an Adapter, which retrieves data from an external source
and creates a View that represents each data entry.

Android provides several subclasses of Adapter that are useful for
retrieving different kinds of data and building views for an AdapterView ( i.e.
ListView or GridView). The common adapters are ArrayAdapter,Base
Adapter,CursorAdapter, SimpleCursorAdapter,SpinnerAdapter and WrapperListAdapter.
We will see separate examples for both the adapters.

ListView Attributes

Following are the important attributes specific to GridView −

 


  

  

Sr.No

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:divider

This is drawable or color to
  draw between list items.

 

  

  

3

  

  

android:dividerHeight

This specifies height of the
  divider. This could be in px, dp, sp, in, or mm.

 

  

  

4

  

  

android:entries

Specifies the reference to an
  array resource that will populate the ListView.

 

  

  

5

  

  

android:footerDividersEnabled

When set to false, the ListView
  will not draw the divider before each footer view. The default value is true.

 

  

  

6

  

  

android:headerDividersEnabled

When set to false, the ListView
  will not draw the divider after each header view. The default value is true.

 





Android GridView shows
items in two-dimensional scrolling grid (rows & columns) and the grid items
are not necessarily predetermined but they automatically inserted to the layout
using a ListAdapter



GRID VIEW

An
adapter actually bridges between UI components and the data source that fill
data into UI Component. Adapter can be used to supply the data to like spinner,
list view, grid view etc.

The ListView and GridView are
subclasses of AdapterView and they can be populated by binding
them to an Adapter, which retrieves data from an external source
and creates a View that represents each data entry.




GridView Attributes

Following are the important attributes specific to GridView −

 


  

  

Sr.No

  

  

Attribute & Description

 

  

  

1

  

  

android:id

This is the ID which uniquely
  identifies the layout.

 

  

  

2

  

  

android:columnWidth

This specifies the fixed width
  for each column. This could be in px, dp, sp, in, or mm.

 

  

  

3

  

  

android:gravity

Specifies the gravity within
  each cell. Possible values are top, bottom, left, right, center,
  center_vertical, center_horizontal etc.

 

  

  

4

  

  

android:horizontalSpacing

Defines the default horizontal
  spacing between columns. This could be in px, dp, sp, in, or mm.

 

  

  

5

  

  

android:numColumns

Defines how many columns to
  show. May be an integer value, such as "100" or auto_fit which
  means display as many columns as possible to fill the available space.

 

  

  

6

  

  

android:stretchMode

Defines how columns should
  stretch to fill the available empty space, if any. This must be either of the
  values −

·     
  none − Stretching is disabled.

·     
  spacingWidth − The spacing between each
  column is stretched.

·     
  columnWidth − Each column is stretched
  equally.

·     
  spacingWidthUniform − The spacing between
  each column is uniformly stretched..

 

  

  

7

  

  

android:verticalSpacing

Defines the default vertical
  spacing between rows. This could be in px, dp, sp, in, or mm.

 





ð
Android Intent Tutorial



Android Intent is the message that is
passed between components such as activities, content providers, broadcast
receivers, services etc.

It is generally used with
startActivity() method to invoke activity, broadcast receivers etc.

The dictionary meaning of
intent is intention or purpose. So, it can be described as the
intention to do action.

The LabeledIntent is the
subclass of android.content.Intent class.

Android intents are mainly
used to:

Start the service
Launch an activity
Display a web page
Display a list of contacts
Broadcast a message
Dial a phone call etc.


Types
of Android Intents

There
are two types of intents in android: implicit and explicit.

1) Implicit Intent

Implicit Intent doesn't specifiy the component.
In such case, intent provides information of available components provided by
the system that is to be invoked.

For
example, you may write the following code to view the webpage.

1.    Intent intent=new Intent(Intent.ACTION_VIEW);  

2.   
intent.setData(Uri.parse("http://www.javatpoint.com"));  

3.   
startActivity(intent);  

2) Explicit Intent

Explicit Intent specifies the component. In
such case, intent provides the external class to be invoked.

1.    Intent i = new Intent(getApplicationContext(), ActivityTwo.class);  

2.   
startActivity(i);  

To
get the full code of explicit intent, visit the next page.






Android Implicit Intent Example

Let's
see the simple example of implicit intent that displays a web page.

activity_main.xml

File: activity_main.xml

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

2.    <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"  

3.   
    xmlns:app="http://schemas.android.com/apk/res-auto"  

4.   
    xmlns:tools="http://schemas.android.com/tools"  

5.   
    android:layout_width="match_parent"  

6.   
    android:layout_height="match_parent"  

7.   
    tools:context="example.javatpoint.com.implicitintent.MainActivity">  

8.   
  

9.   
    <EditText  

10.         android:id="@+id/editText"  

11.         android:layout_width="wrap_content"  

12.         android:layout_height="wrap_content"  

13.         android:layout_marginEnd="8dp"  

14.         android:layout_marginStart="8dp"  

15.         android:layout_marginTop="60dp"  

16.         android:ems="10"  

17.         app:layout_constraintEnd_toEndOf="parent"  

18.         app:layout_constraintHorizontal_bias="0.575"  

19.         app:layout_constraintStart_toStartOf="parent"  

20.         app:layout_constraintTop_toTopOf="parent" />  

21.   

22.     <Button  

23.         android:id="@+id/button"  

24.         android:layout_width="wrap_content"  

25.         android:layout_height="wrap_content"  

26.         android:layout_marginRight="8dp"  

27.         android:layout_marginLeft="156dp"  

28.         android:layout_marginTop="172dp"  

29.         android:text="Visit"  

30.         app:layout_constraintEnd_toEndOf="parent"  

31.         app:layout_constraintHorizontal_bias="0.0"  

32.         app:layout_constraintStart_toStartOf="parent"  

33.         app:layout_constraintTop_toBottomOf="@+id/editText" />  

34. </android.support.constraint.ConstraintLayout>  





 size=1 width="100%" noshade style='color:#D4D4D4' align=center>


Activity class

File: MainActivity.java

1.    package example.javatpoint.com.implicitintent;  

2.   
  

3.    import android.content.Intent;  

4.    import android.net.Uri;  

5.    import android.support.v7.app.AppCompatActivity;  

6.    import android.os.Bundle;  

7.    import android.view.View;  

8.    import android.widget.Button;  

9.    import android.widget.EditText;  

10.   

11. public class MainActivity extends AppCompatActivity {  

12.   

13.     Button button;  

14.     EditText editText;  

15.   

16.     @Override  

17.     protected void onCreate(Bundle savedInstanceState) {  

18.         super.onCreate(savedInstanceState);  

19.         setContentView(R.layout.activity_main);  

20.   

21.         button = findViewById(R.id.button);  

22.         editText =  findViewById(R.id.editText);  

23.   

24.         button.setOnClickListener(new View.OnClickListener() {  

25.             @Override  

26.             public void onClick(View view) {  

27.                 String url=editText.getText().toString();  

28.                 Intent intent=new Intent(Intent.ACTION_VIEW, Uri.parse(url));  

29.                 startActivity(intent);  

30.             }  

31.         });  

32.     }  

33. }  

Output: