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1- Introduction
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This document is based on:
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2- What is Intent?
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Intents are asynchronous messages which allow application components to request functionality from other Android components. Intents allow you to interact with components from the same applications as well as with components contributed by other applications. For example, an activity can start an external activity for taking a picture.
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Intents are objects of the
android.content.Intent type. Your code can send them to the Android system defining the components you are targeting.
For example, via the
startActivity() method you can define that the intent should be used to start an activity. In the target
Activity, via
startActivity() method, you can determine the sender's intention to start this
Activity.
An intent can contain data via a
Bundle. This data can be used by the receiving component.
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Intent can be used to:
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- Start an Activity
- Start sub-activity.
- Start a Service.
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After learning about
Intent, you can find more details about
Android Service at:
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3- The types of Intent
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Android supports explicit and implicit intents.
An application can define the target component directly in the intent (explicit intent) or ask the Android system to evaluate registered components based on the intent data (implicit intents).
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4- Explicit Intent
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Explicit intents: These explicitly specify the name of the target component to handle the intent; in these, the optional component name field (above) is set to a particular value, through the
setComponent() or
setClass() methods.
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Create Intent example:
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// Create the Intent with the target of Greeting Activity.
// Intent(FirstActivity, SecondActivity.class)
Intent intent = new Intent(this,GreetingActivity.class);
// The data attached
intent.putExtra("firstName",firstName);
intent.putExtra("lastName", lastName);
// Start Activity (GreetingActivity)
// (No need feedback from the activity is called)
this.startActivity(intent);
// Start Activity and will have a feedback from the activity is called.
this.startActivityForResult(intent, MY_REQUEST_CODE);
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Or:
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// Way 1.
Intent mIntent = new Intent(this, GreetingActivity.class);
Bundle extras = mIntent.getExtras();
extras.putString("firstName", "<firstName>");
extras.putString("látName", "<lastName>");
// Way 2.
Intent mIntent2 = new Intent(this, GreetingActivity.class);
Bundle mBundle = new Bundle();
mBundle.putString("firstName", "<firstName>");
mBundle.putString("látName", "<lastName>");
mIntent2.putExtras(mBundle);
// Way 3:
// Using putExtra()
Intent mIntent3 = new Intent(this, GreetingActivity.class);
mIntent3.putExtra("firstName", "<firstName>");
mIntent3.putExtra("látName", "<lastName>");
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In the target
Activity:
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Intent intent = this.getIntent();
String firstName= intent.getStringExtra("firstName");
String lastName = intent.getStringExtra("lastName");
// Or
Bundle extras = this.getIntent().getExtras();
String firstName1 = extras.getString("firstName");
String lastName2 = extras.getString("lastName");
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OK, you can see the following simple example:
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5- Explicit Intent example
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This is the model of the example:
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Create
"Empty Activity" project named
ExplicitIntentExample:
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By double-clicking on the components on the interface, you can set the ID and text for them:
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EditText 1:
- ID: text_firstName
- Properties
- layout_width: fill_parent
EditText 2:
- ID: text_lastName
- Properties
- layout_width: fill_parent
TextView:
- ID: text_feedback
- Text: <Feedback>
- Properties:
- layout_width: fill_parent
- gravity: center_horizontal
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Button:
- ID: button_greeting
- Text: Show Greeting
- Properties:
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activity_main.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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/text_firstName"
android:layout_alignParentTop="true"
android:layout_marginTop="66dp"
android:layout_centerHorizontal="true" />
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/text_lastName"
android:layout_below="@+id/text_firstName"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Show Greeting"
android:id="@+id/button_greeting"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="132dp"
android:onClick="showGreeting" />
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="<Feedback>"
android:id="@+id/text_feedback"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="59dp"
android:gravity="center_horizontal" />
</RelativeLayout>
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When users click the button, the program will call a other Activity to displays a greeting. You need to create an Activity with name
GreetingActivity.
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- File/New/Activity/Empty Activity
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Change the attributes for components on the interface:
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TextView
- ID: text_greeting
- Text: <Greeting>
- Properties:
- layout_width: fill_parent
- gravity: center_horizontal
Button:
- ID: button_back
- Properties
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activity_greeting.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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="org.o7planning.explicitintentexample.GreetingActivity">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="<Greeting>"
android:id="@+id/text_greeting"
android:layout_marginBottom="65dp"
android:layout_above="@+id/button_back"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:gravity="center_horizontal" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Back"
android:id="@+id/button_back"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:onClick="backClicked" />
</RelativeLayout>
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MainActivity.java
package org.o7planning.explicitintentexample;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private EditText textFirstName;
private EditText textLastName;
private TextView textFeedback;
public static final int MY_REQUEST_CODE = 100;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.textFirstName = (EditText)this.findViewById(R.id.text_firstName);
this.textLastName = (EditText)this.findViewById(R.id.text_lastName);
this.textFeedback = (TextView)this.findViewById(R.id.text_feedback);
}
// When 'Greeting Activity' completed, it sends back a feedback.
// (If you have started it by startActivityForResult())
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (resultCode == Activity.RESULT_OK && requestCode == MY_REQUEST_CODE ) {
String feedback = data.getStringExtra("feedback");
this.textFeedback.setText(feedback);
} else {
this.textFeedback.setText("!?");
}
}
// The method is called when the user clicks on "Show Greeting" button.
public void showGreeting(View view) {
String firstName= this.textFirstName.getText().toString();
String lastName= this.textLastName.getText().toString();
Intent intent = new Intent(this,GreetingActivity.class);
intent.putExtra("firstName", firstName);
intent.putExtra("lastName", lastName);
// Start Activity and no need feedback.
// this.startActivity(intent);
// Start Activity and get feedback.
this.startActivityForResult(intent, MY_REQUEST_CODE);
}
}
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GreetingActivity.java
package org.o7planning.explicitintentexample;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class GreetingActivity extends AppCompatActivity {
private String firstName;
private String lastName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_greeting);
// Intent is passed into
Intent intent = this.getIntent();
this.firstName= intent.getStringExtra("firstName");
this.lastName = intent.getStringExtra("lastName");
String greeting = "Hello "+ firstName+" "+ lastName;
TextView textGreeting =(TextView) this.findViewById(R.id.text_greeting);
textGreeting.setText(greeting);
}
// When completed this Activity, send feedback to the caller.
@Override
public void finish() {
// Prepare data intent
Intent data = new Intent();
data.putExtra("feedback", "I'm "+ this.firstName+", Hi!");
// Activity finished ok, return the data
this.setResult(Activity.RESULT_OK, data);
super.finish();
}
// The method is called when the user clicks the Back button.
public void backClicked(View view) {
// Calling onBackPressed().
// Gọi phương thức onBackPressed().
this.onBackPressed();
}
}
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Running application:
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6- Intent Filter
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When you create new an
Activity or Service, you need to declare it to
AndroidManifest.xml, normally, when you create it with helps of wizard in
Android Studio, registration code is automatically created in
AndroidManifest.xml. For example:
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You may notice that in the declaration of Activity on
AndroidManifest.xml may have
<intent-filter> tag, this tag specifies the type of Intent sent to it (Activity) that it can accept.
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When you create an implicit intent, the Android system finds the appropriate component to start by comparing the contents of the intent to the intent filters declared in the manifest file of other apps on the device. If the intent matches an intent filter, the system starts that component and delivers it the Intent object.
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Example:
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** AndroidManifest.xml **
.....
<activity android:name=".HelloWorld"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.VIEW"/>
<category android:name="android.intent.category.DEFAULT"/>
<category android:name="android.intent.category.BROWSABLE"/>
<data android:scheme="http" android:host="o7planning.org"/>
</intent-filter>
</activity>
...
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For example, create an implicit intent can call the above Activity (It matches the intent filters).
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// An implicit intent, requested to view a URL
Intent intent = new Intent (Intent.ACTION_VIEW, Uri.parse("//o7planning.org"));
startActivity(intent);
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7- Implicit intent
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Implicit intents: These do not specify a target component, but include enough information for the system to determine which of the available components is best to run for that intent. Consider an app that lists the available restaurants near you. When you click a particular restaurant option, the application has to ask another application to display the route to that restaurant. To achieve this, it could either send an explicit intent directly to the
Google Maps application, or send an implicit intent, which would be delivered to any application that provides the Maps functionality (e.g., Yahoo Maps).
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8- Simple example with the implicit intent
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This simple example, when you click a
Button which requires to see website by
URL, you create an implicitly Intent, Intent sent to the Android system to decide which components will be opened , maybe in your equipment installs many different browsers (Firefox, Chrome, ..), the device will open it in your default browser or your preferred browser
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In addition examples also include:
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Create Android project with name
"ImplicitIntentExample".
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Set ID, Text for Button:
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Button 1:
- ID: button_google
- Text: Go Google
- Properties:
Button 2:
- ID: button_email
- Text: Send Email
- Properties:
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activity_main.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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Go Google"
android:id="@+id/button_google"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="86dp"
android:onClick="goGoogle" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Send Email"
android:id="@+id/button_email"
android:layout_below="@+id/button_google"
android:layout_centerHorizontal="true"
android:layout_marginTop="45dp"
android:onClick="sendEmail" />
</RelativeLayout>
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MainActivity.java
package org.o7planning.implicitintentexample;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
// The method is called when the user clicks on "Go Google" button.
public void goGoogle(View view) {
String url="http://google.com";
// An implicit intent, request a URL.
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
this.startActivity(intent);
}
// The method is called when the user clicks on "Send Email" button.
public void sendEmail(View view) {
// List of recipients
String[] recipients=new String[]{"[email protected]"};
String subject="Hi, how are you!";
String content ="This is my test email";
Intent intentEmail = new Intent(Intent.ACTION_SEND, Uri.parse("mailto:"));
intentEmail.putExtra(Intent.EXTRA_EMAIL, recipients);
intentEmail.putExtra(Intent.EXTRA_SUBJECT, subject);
intentEmail.putExtra(Intent.EXTRA_TEXT, content);
intentEmail.setType("text/plain");
startActivity(Intent.createChooser(intentEmail, "Choose an email client from..."));
}
}
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Running app:
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- Send Email (VIEW SLIDER).
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9- Implicit intent example, photographed from the camera and save to file
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An example with implicit Intent, when you click a button, the application sent to the
Android system a request to take a photograph by
Camera and save image to a file.
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