1. Android Intents
Intents
are asynchronous messages which allow Android components to request functionality from other components of the Android system. For example an Activity
can send an Intents
to the Android system which starts another Activity
.Therefore
Intents
allow to combine loosely coupled components to perform certain tasks.Intents
can be used to signal to the Android system that a certain event has occurred. Other components in Android can register to this event and will get notified.Intents
are instances of the android.content.Intent
class.Intents
are send to the Android system. Depending on how the Intent
was constructed the Android system will run an receiver determination and determine what to do.An
Intent
can also contain data. This data can be used by the receiving component. For example your application can calls via an Intent
a browser component. As data is it may send the URL to the browser component.Android supports explicit and implicit
Intents
.
Explicit
The following shows an explicit
Explicit
Intents
explicitly names the component which should be called by the Android system, by using the Java class as identifier.The following shows an explicit
Intent
. If that Intent
is correctly send to the Android system, it will start the associated class.Intent i = new Intent(this, ActivityTwo.class); i.putExtra("Value1", "This value one for ActivityTwo "); i.putExtra("Value2", "This value two ActivityTwo");
Explicit
Intents
are typically used within on application as the classes in an application are controlled by the application developer.
Implicit
For example the following tells the Android system to view a webpage. Typically the web browser is registered to this
If these
If only one component is found, Android starts this component directly. If several components are identifier by the Android system, the user will get an selection dialog and can decide which component should be used for the
Intents
do not specify the Java class which should be called. They specify the action which should be performed and optionally an URI which should be used for this action.For example the following tells the Android system to view a webpage. Typically the web browser is registered to this
Intent
but other component could also register themself to this event.Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.vogella.com"));
If these
Intents
are send to the Android system it searches for all components which are registered for the specific action and the data type.If only one component is found, Android starts this component directly. If several components are identifier by the Android system, the user will get an selection dialog and can decide which component should be used for the
Intent
.
An implicit
Explicit and implicit
The component which creates the
For example you can trigger all components which have been registered to send some data via the
The component which receives the
Intent
contains the Action and optional the URI. The receiving component can get this information via the getAction()
and getData()
methods.Explicit and implicit
Intents
can also contain additional data. This data call be filled by the component which creates the Intent
. It can and can get extracted by the component which receives the Intent
.The component which creates the
Intent
can add data to it via the overloaded putExtra()
method. Extras are key/value pairs; the key is always a String. As value you can use the primitive data types (int, float,..), String, Bundle, Parceable and Serializable.For example you can trigger all components which have been registered to send some data via the
new Intent(Intent.ACTION_SEND)
This Intent
determines possible receivers via the type. What is send it defined via the putExtra
method. You can use any String as key, the following uses the keys which are predefined for the ACTION_SEND intent.Intent sharingIntent = new Intent(Intent.ACTION_SEND); sharingIntent.setType("text/plain"); sharingIntent.putExtra(android.content.Intent.EXTRA_TEXT, "News for you!"); // createChooser is a convenience method to create // an Chooser Intent with a Title startActivity(Intent.createChooser(sharingIntent,"Share this using"));
The component which receives the
Intent
can use the getIntent().getExtras()
method call to get the extra data.Bundle extras = getIntent().getExtras(); if (extras == null) { return; } // Get data via the key String value1 = extras.getString(Intent.EXTRA_TEXT); if (value1 != null) { // Do something with the data }
If you send an
To start an
If you call an
Intent
to the Android system, Android requires that you tell it to which type of component your Intent
should be send.To start an
Activity
use the method startActivity(Intent)
. This method is defined on theContext
object and available in every Activity
object.If you call an
Activity
with the startActivity(Intent)
method the caller requires no result from the called Activity
.
If you need some information from the called
If you use the
If the Sub-Activity is finished it can send data back to its caller via Intent. This is done in the
Once the
Activity
use the startActivityForResult()
method.public void onClick(View view) { Intent i = new Intent(this, ActivityTwo.class); i.putExtra("Value1", "This value one for ActivityTwo "); i.putExtra("Value2", "This value two ActivityTwo"); // Set the request code to any code you like, you can identify the // callback via this code startActivityForResult(i, REQUEST_CODE); }
If you use the
startActivityForResult()
method then the started Activity
is called a Sub-Activity
.If the Sub-Activity is finished it can send data back to its caller via Intent. This is done in the
finish()
method.@Override public void finish() { // Prepare data intent Intent data = new Intent(); data.putExtra("returnKey1", "Swinging on a star. "); data.putExtra("returnKey2", "You could be better then you are. "); // Activity finished ok, return the data setResult(RESULT_OK, data); super.finish(); }
Once the
Sub-Activity
finished, the onActivityResult()
method in the calling Activity
will be called.@Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) { if (data.hasExtra("returnKey1")) { Toast.makeText(this, data.getExtras().getString("returnKey1"), Toast.LENGTH_SHORT).show(); } } }
for more about intents go to http://www.vogella.com/articles/AndroidIntent/article.html or http://developer.android.com/guide/topics/intents/intents-filters.html
2 comments:
Nice Stuff:) Very Simple and Perfect
Thank you Sonu :)
Post a Comment