Intents:
Intent is an abstract description of
operation to be performed.
Intents are asynchronous messages which
allow android components to request functionality from other components in the
android system and it is also used to pass the control from one activity to
another activity.
Intents are
2 types:
Explicit
intents
Implicit
intents
Explicit
intents:
Explicit
intents:
If we want
to navigate control from one activity to another activity, we have to use
explicit intents.
Intent i=new Intent(context c,class);
startActivity(i);
Download source code
http://www.4shared.com/rar/VseQTmEN/Intent.html
startActivityForResult():
it supports only for bi directional communication.
How to use this? You want to learn.... lets see this example
package com.example.intentresult;
//Srinivas Nidadavolu // www.mobengineers.com //
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
public class MainActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void GoNext(View v)
{
Intent i=new Intent(MainActivity.this,SecondActivity.class);
startActivityForResult(i, 1);
}
}
activity_main.xml
why i have written startActivityForResult(i,1);
you know intent class is used to navigate from one activity to other activity. But, if we want to goback to previous activity, we have to get the result and pass it to next activity, with that result, we can move to back activity.
why i have written 1 as second parameter.
i.e id of the intent. we can give any number here.
0 or 1 or 2 or 101 or 200 or..................... any number, not only these.
<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" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="163dp"
android:text="Button"
android:onClick="GoNext"
/>
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="31dp"
android:text="Hello This is the first screen"
android:textSize="25sp" />
</RelativeLayout>
package com.example.intentresult;
//Srinivas Nidadavolu // www.mobengineers.com //
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class SecondActivity extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
}
public void GoBack(View v)
{
Intent i=new Intent();
setResult(RESULT_OK,i);
finish();
}
}
second.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Second Screen"
android:textSize="25sp" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="GoBack"
android:text="Go Back" />
</LinearLayout>
Ex:
public class MainActivity extends Activity {
EditText et;
String name;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et=(EditText)findViewById(R.id.editText1) ;
}
public void goToWelcome(View v)
{
if(et!=null && et.getText().length()!=0)
{
name = et.getText().toString();
}
else
{
name="guest";
}
Intent i=new Intent(MainActivity.this,NextAct.class);
i.putExtra("username", name);
startActivity(i);
}
}
package com.example.intent;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
public class NextAct extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.next);
TextView tv=(TextView)findViewById(R.id.textView1);
Intent i=getIntent();
String usertext=(String) i.getSerializableExtra("username");
tv.setText(usertext);
}
}
main.xml
<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" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginRight="25dp"
android:layout_marginTop="26dp"
android:text="Enter Username" />
<EditText
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/textView1"
android:layout_marginLeft="26dp"
android:layout_marginTop="26dp"
android:hint="Enter Username"
android:ems="10" >
<requestFocus />
</EditText>
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/editText1"
android:layout_below="@+id/editText1"
android:layout_marginRight="77dp"
android:layout_marginTop="43dp"
android:onClick="goToWelcome"
android:text="Go" />
</RelativeLayout>
next.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginRight="104dp"
android:layout_marginTop="97dp"
android:text="TextView" />
</RelativeLayout>
Implicit
Intents:
If we want
to interact with default software components and hardware components, we have
to use implicit intents.
for opening browser
Intent i=new Intent(Intent.ACTION_VIEW,Uri.parse("http://www.mobengineers.com"));
startActivity(i);
we have to declare internet permission in manifest file.
for calling number
Intent i=new Intent(Intent.ACTION_CALL,Uri.parse("tel:9848012345"));
startActivity(i);
we have to declare permission for call in manifest file.
<uses-permission android:name="android.permission.CALL_PHONE"></uses-permission>
for opening camera
Intent i=new Intent("android.media.action.IMAGE_CAPTURE"));
startActivityForResult(i,0);
