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Which function does intent have? [duplicate]

This question already has answers here:
What is an Intent in Android?
(14 answers)
Closed 8 years ago.
I dont know much about intent (or android) so.. Can someone please explain me what is it exactly? i have search on the internet, A LOT.
Also what does each line of this code do?
Intent intent = new Intent (this, DisplayMessageActivity.class);
intent.putExtra("a", "b");
Thanks in advance

I suggest reading Android Intents
You couldn't have search for very long, since this is very basic topic.
I suggest you read more of Android's API guides.
Line 1 = Create message that describes what to do, in this case start "DisplayMessagActivity"
Line 2 = Add content to the message

Intent intent = new Intent (this, DisplayMessageActivity.class);
For this line, its function is to create a navigation from the current activity/page to the displaymessageactivity page.
it is like from here to there.
For this intent.putExtra("a", "b"); the purpose of this is to put like a temp storage/variable to pass to the next page for retrieval. In this case, you put the value "b" in the variable "a". With this method, you can use the value on the other activity or page.
All the above are just storing of info, it is not executed yet. if you want to execute the intent do the following
startActivity(intent);

The best example to state the behavior of Intent is it behaves like a POSTMAN that delivers message to the stated address.
Whether it may be calling service ,BroadCastRecivers ,Activity they are used in number of occassion.
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.
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.
An intent can contain data via a Bundle. This data can be used by the
receiving component.
Intents can be used to start Service, call Activty, call Sub Activity, transfer the data between Activity or retrieve the data from Activity

Android- customize built-in Component?

Let's say I create an intent to view a Google map like so:
Intent intent = new Intent("android.intent.ACTION_VIEW");
intent.setComponent(ComponentName.unflattenFromString("com.google.android.apps.maps/com.google.android.maps.MapsActivity"));
intent.addCategory(android.intent.category.LAUNCHER);
intent.setData("Your Google My Map URL HERE");
startActivity(intent);
Is there any way to customize this MapsActivity component, or just get a handle in it to control/query it at all, or would I have to start from scratch to do this?

Is there any way to customize this MapsActivity component, or just get a handle in it to control/query it at all, or would I have to start from scratch to do this?
No. You have no right to hack into other apps, any more than they have the right to hack into yours. Use MapView.
BTW, your example code there is scary. Never reference third-party apps by component name, as your code will break if that app refactors its code. Never add the LAUNCHER category to an Intent unless you are actually a launcher (e.g., a home screen). And bear in mind that this recipe is neither documented nor supported by Google.

Trapping filtered Intents from android

From my understanding, if an intent is invoked implicitly, android matches the intent object's contents against all intent filters in the following order: component, action, data and category, filtering out non-matching intents at each step. At this point if there are multiple intents filtered out, then it brings up the activity chooser.
Is there a way by which I can trap the final filtered result and do further filtering based on Extras and Flags? Would ResolveInfo be of any help to me in this case?
In effect, I want to process my custom logic before android brings up the Activity chooser.
Can someone please point me in the right direction, maybe a place in the android source code which helps me to do the above?!
Thanks a lot!

If you are the one calling startActivity(), you can use PackageManager and queryIntentActivities() to find out what the chooser would wind up showing. You can then roll your own chooser if you, er, choose.
If you are trying to intercept the starting of any and all activities on the device, this is not possible.

2 Intent Filters, 1 Activity - Which opened it?

Is there a way to know which Intent Filter is responsible for launching an Activity which has two Intent Filters defined in AndroidManifest.xml? I want a slightly different set of logic, but not enough that should require a whole new Activity.
Thanks!

Never mind, found it. Just wasn't looking hard enough...
Using this.getIntent().getAction() in your Activity will spit out exactly what I was looking for, a String to identify which Intent Filter Action opened it.

Launching external application from my app

I would like to launch an app the user selects from within my application. However, I'm not sure how I'd go about doing this. I've tried this:
Intent intent = new Intent();
intent.setAction(Contacts.Intents.SHOW_OR_CREATE_CONTACT);
startActivity(intent);
But this seems to throw an error and force close my application. I also tried adding:
<action android:name="Contacts.Intents.SHOW_OR_CREATE_CONTACT"/>
in the AndroidManifest file, but to no avail.
A look at Logcat shows that it's an "IOexception - no such file or directory". A couple of questions arise from this. I read through the Android docs and noticed that the Contact.Intents class is deprecated. However, it's successor, ContactContracts is aimed at API level 5 whereas I'm targeting API level 3. Could this be the problem? Also, I've hardcoded this application into the code. Is there a way to retrieve the intents of any application the user selects so that they can be launched?

You need to pass extra information into the intent to tell Android what you want to show or create. Otherwise Android doesn't know what activity to start and (presumably in your case) throws an ActivityNotFoundException.
For a contact, you use the generic Intent.ACTION_INSERT_OR_EDIT then use the MIME type of an individual contact (Contacts.People.CONTENT_ITEM_TYPE).
For example:
Intent intent = new Intent(Intent.ACTION_INSERT_OR_EDIT);
intent.setType(People.CONTENT_ITEM_TYPE);
intent.putExtra(Contacts.Intents.Insert.PHONE, "+1234567890");
intent.putExtra(Contacts.Intents.Insert.PHONE_TYPE, Contacts.PhonesColumns.TYPE_MOBILE);
That will bring up the contacts app, prompting you to select an existing contact to add the phone number to, or to create a new contact.
You don't need to add anything special to your manifest to start external activities. Only if you were to directly manipulate the contacts ContentProvider would you need to add the appropriate CONTACT permissions to your manifest.

I use this code for that purpose:
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setClassName("com.android.settings", "com.android.settings.Settings");
startActivity(intent);
This will launch the Settings app, you can use these also:
intent.setClassName("com.android.music", "com.android.music.MediaPlaybackActivityStarter");
intent.setClassName("com.android.contacts", "com.android.contacts.DialtactsContactsEntryActivity");
intent.setClassName("com.android.contacts", "com.android.contacts.DialtactsActivity");
The first starts the default music app, the second the contacts, and the third the dialer.
Hope this helps.

You need to pass in valid arguments to the apps you start. A lot of apps expect the data URI and / or certain extras to be valid.

Please try the following code:
Intent intent = new Intent(Contacts.Intents.SHOW_OR_CREATE_CONTACT);
this.startActivity(intent);
(sorry if there is something wrong on the syntax, I dont have android in this computer)
And remove the action from the manifest. that is not needed.
The action method is used for something else.
For more info, please look at the android site: http://developer.android.com/reference/android/content/Intent.html
Daniel

The activity you are calling should appear not only in the Manifest for its own package, but in the Manifest for the CALLING package, too.