Intents:
Intents are asynchronous message which allow application
components to request functionality from other Android components.
The dictionary meaning of
Intent is Intention or purpose. So it
can be described as the intention to do action.
Android
intent
is the message that is passed between components such as content providers, activities,
broadcast recievers, services etc.
Android
Intents
are mainly used to:
·
start
a service
·
dial
a phone call
·
Broadcast
a message
·
Display
a list of contacts
·
Display
a web page
The LabeledIntent is the
subclass of android.content.Intent class.
An intent can contain
data via a Bundle. This data can be used
by the receiving component.
In Android the reuse of
other application components is a concept known as task. An application can
access other Android components to achieve a task.
Starting
activities or services:
To start an activity you
have to use a method startActivity().This
method is defined the Context object which Activity extends.
The following code
demonstrates how you can start activity via intent.
Intent i = new Intent (this,Login.class);
startActivity(i);
Activities which are
started by other android activities are called sub-activities. To start a
service via intents, use the startService(Intent)
method call.
Types
of Android Intents:
There are two types of
Intents in android which are as follows:
·
Implicit
Intent
·
Explicit
Intent
Implicit
Intent:
These Intents do not name
a target and the field for the component name is left blank. Implicit Intents
are also used to activate components of other activities.
for example-
Intent i= new Intent();
i.setAction(android.content.Intent.ACTION_VIEW);
i.setData(ContactsContracts.CONTENT_URI);
startActivity(i);
Explicit
Intent:
Explicit intent going to
be connected intenal world of application. Explicit Intent specifies the
components. In such case,intent provides the external class to be invoked.
For example-
Intent i= new Intent();
startActivity(this,First.class));
Let's see a simple example
of Intent that take from one activity to another activity.
First
Activity XML:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center_horizontal"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingBottom="@dimen/activity_horizontal_margin"
android:gravity="center_horizontal"
android:background="#bcbaba">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?
android:attr/textAppearanceSmall"
android:text="Email"
android:id="@+id/textView9"
android:layout_marginBottom="4dp"
android:textSize="20sp"
android:textColor="#ffffff" />
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#fff"
android:layout_weight="1">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/imageView3"
android:background="@drawable/email_icon"
android:layout_gravity="left|center_horizontal" />
<EditText
style="@style/signupEditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:ems="10"
android:id="@+id/edtEmail"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:hint="Email"
android:gravity="center_vertical"
android:paddingTop="5dp"
android:paddingBottom="5dp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:paddingTop="5dp">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceSmall"
android:text="Password"
android:id="@+id/textView10"
android:layout_marginBottom="4dp"
android:textSize="20sp"
android:textColor="#ffffff" />
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#fff"
android:layout_weight="1" >
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/imageView9"
android:background="@drawable/password_icon"
android:layout_gravity="left|center_horizontal" />
<EditText
style="@style/signupEditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:id="@+id/edtPassword"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:hint="*******"
android:gravity="center_vertical"
android:inputType="textPassword"
android:paddingTop="5dp"
android:paddingBottom="5dp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal">
</LinearLayout>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btnSignIn"
android:onClick="onClick"
android:layout_gravity="center_horizontal"
android:gravity="center"
android:background="#fff"
android:layout_marginTop="25dp"
android:text="LOGIN"
android:textColor="#238996"
android:textSize="18sp" />
</LinearLayout>
</LinearLayout>
Second
Activity XML:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.tecorb.eat_we_go.Second"
android:background="#c5bebe">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Welcome"
android:id="@+id/textView6"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="195dp"
android:textStyle="bold"
android:textSize="30sp"
android:textColor="#1d1717" />
</RelativeLayout>
First.java
package com.example.tecorb.eat_we_go;
import
android.content.Intent;
import
android.support.v7.app.AppCompatActivity;
import
android.os.Bundle;
import
android.view.View;
import
android.widget.Button;
import
android.widget.EditText;
public
class First extends AppCompatActivity
{
EditText edtEmail,edtPassword;
Button btnSignIn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_first);
edtEmail = (EditText) findViewById(R.id.edtEmail);
edtPassword = (EditText) findViewById(R.id.edtPassword);
btnSignIn=(Button)findViewById(R.id.btnSignIn);
btnSignIn.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
Intent intent=new Intent();
startActivity(new Intent(getApplicationContext(), Second.class));
}
});
}
}
In above example, there
are two xml activity in which first is our main and login activity in which we
take two edit text for email and password and a login button to submit the data
by which on click we reach at the other activity where we take an edit text and
show welcome as a text.
With the help of java we
write code and by intent we connect two activities as first activity with the
second.
