I've read plenty of doc, but I still can't figure it out.
Are we allowed to start a 3rd party app(NON SYSTEM APP like as alarm, notification. etc) with a pending intent?
i.e.:
App1
create pending intent
start a non system app and send pending intent
App2
execute its own code
call pending intent to start App1
I haven't found 1 single example doing this. And according to the doc. you can pass a pending intent to a 3rd party app. It does not specify a system app
does it make sense?
Yes, you may launch anything you want with a PendingIntent. As long as the component you want to start is exported (publicly available).
I was looking at the documentation for PendingIntent.getBroadcast(Context, int, Intent, int) and it mentions that...
For security reasons, the Intent you supply here should almost always be an explicit intent, that is specify an explicit component to be delivered to through Intent.setClass
What exactly are the security reasons? What makes explicit Intents more secure if other applications can still create one using only your package name and the component's name?
I've seen the report at NIST.gov about a PendingIntent-based security vulnerability that affected all of Android 4.x, where a malicious app could send Intents as the SYSTEM user. However, I'm not sure if the same concerns apply to my app.
If an Intent is handled by a BroadcastReceiver and the Intent isn't used to pass data (as extras, for example,) is there still a risk?
My guess is that what they really meant was:
For security reasons, the Intent you supply here should almost always be an explicit Intent pointing to a non-exported component, that is specify an explicit component to be delivered to through Intent.setClass
Your concern about "other applications can still create one using only your package name and the component's name" is only valid if the component is exported. For a BroadcastReceiver, it will be exported by default only if it has an <intent-filter> (or IntentFilter, if registering via registerReceiver()).
If an Intent is handled by a BroadcastReceiver and the Intent isn't used to pass data (as extras, for example,) is there still a risk?
Off the cuff, there are two risks with using implicit Intents:
On the sending side, anyone can respond to your broadcast. While you might think that the mere existence of the broadcast is not a privacy/security leak — and in your specific case, it might not be a leak — that is not universally true.
On the receiving side, if your component is exported (the default if it can handle an implicit Intent), other parties could send you fake broadcasts, perhaps tricking you into doing something unfortunate.
I need to know if there is a way to obtain the intent filter of an applicaction (activity) and the actual name of the application as we see it on the android launcher screen, through a broadcast it sends to a service.
The service receives the broadcast through its broadcast receiver, then it needs to know the applicatione's name and its intent filter in order to do some work with that information. Is there a way to find this out through the intent, or does the application need to actually putextras in the intent?
Is there a way to find this out through the intent
Not really, insofar as the Intent has no information about the Intent's origination point.
does the application need to actually putextras in the intent?
Yes, because only the originator of the broadcast knows what is appropriate to be used. After all, an app may have zero, one, or many launcher activities.
You're welcome to try the getCallingUid() and/or getCallingPid() static methods on Binder, to try to automatically derive who the sender is, but this may not work well if there are multiple apps that are using sharedUserId on the device.
Since an application can define same intent filter for different components of the application, it's very likely that intent would match multiple component for the same application. What will happened if it is the case? Will there be any error?
What will happened if it is the case?
Assuming that you are referring to startActivity(), then I would expect all matching activities from your app to appear in the chooser, along with any other activities on the device that match.
Will there be any error?
Probably not. Note, however, that what you are describing is very unusual. Usually, an application only needs one activity to respond to any given Intent structure.
The most suitable intent filter will catch the intent. From the doc:
A different strategy is needed for implicit intents. In the absence of a designated target, the Android system must find the best component (or components) to handle the intent — a single activity or service to perform the requested action or the set of broadcast receivers to respond to the broadcast announcement. It does so by comparing the contents of the Intent object to intent filters, structures associated with components that can potentially receive intents. Filters advertise the capabilities of a component and delimit the intents it can handle. They open the component to the possibility of receiving implicit intents of the advertised type. If a component does not have any intent filters, it can receive only explicit intents. A component with filters can receive both explicit and implicit intents.
...
A filter has fields that parallel the action, data, and category fields of an Intent object. An implicit intent is tested against the filter in all three areas. To be delivered to the component that owns the filter, it must pass all three tests. If it fails even one of them, the Android system won't deliver it to the component — at least not on the basis of that filter. However, since a component can have multiple intent filters, an intent that does not pass through one of a component's filters might make it through on another.
In short: there will be no error. The system tries to find the best match for the intent, which may occasionally involve the user (think about when you install a new browser).
What is an Intent in Android?
Can someone elaborate with an example?
What are the types of Intents, and why we are using them?
Why are Intents so important in Android?
An Intent is an "intention" to perform an action; in other words,
a messaging object you can use to request an action from another app component
An Intent is basically a message to say you did or want something to happen. Depending on the intent, apps or the OS might be listening for it and will react accordingly. Think of it as a blast email to a bunch of friends, in which you tell your friend John to do something, or to friends who can do X ("intent filters"), to do X. The other folks will ignore the email, but John (or friends who can do X) will react to it.
To listen for an broadcast intent (like the phone ringing, or an SMS is received), you implement a broadcast receiver, which will be passed the intent. To declare that you can handle another's app intent like "take picture", you declare an intent filter in your app's manifest file.
If you want to fire off an intent to do something, like pop up the dialer, you fire off an intent saying you will.
What is an Intent ?
An Intent is basically a message that is passed between components (such as Activities, Services, Broadcast Receivers, and Content Providers). So, it is almost equivalent to parameters passed to API calls. The fundamental differences between API calls and invoking components via intents are:
API calls are synchronous while intent-based invocations are
asynchronous.
API calls are compile-time binding while intent-based calls are
run-time binding.
Of course, Intents can be made to work exactly like API calls by using what are called explicit intents, which will be explained later. But more often than not, implicit intents are the way to go and that is what is explained here.
One component that wants to invoke another has to only express its intent to do a job. And any other component that exists and has claimed that it can do such a job through intent-filters, is invoked by the Android platform to accomplish the job. This means, neither components are aware of each other's existence but can still work together to give the desired result for the end-user.
This invisible connection between components is achieved through the combination of intents, intent-filters and the Android platform.
This leads to huge possibilities like:
Mix and match or rather plug and play of components at runtime.
Replacing the inbuilt Android applications with custom developed
applications.
Component level reuse within and across applications.
Service orientation to the most granular level, if I may say.
Here are additional technical details about Intents from the Android documentation.
An intent is an abstract description of an operation to be performed. It can be used with startActivity to launch an Activity, broadcastIntent to send it to any interested BroadcastReceiver components, and startService(Intent) or bindService(Intent, ServiceConnection, int) to communicate with a Background Service.
An Intent provides a facility for performing late runtime binding between the code in different applications. Its most significant use is in the launching of activities, where it can be thought of as the glue between activities. It is basically a passive data structure holding an abstract description of an action to be performed. The primary pieces of information in an intent are:
action
The general action to be performed, such as ACTION_VIEW,
ACTION_EDIT, ACTION_MAIN, etc.
data
The data to operate on, such as a person record in the contacts
database, expressed as a Uri.
Learn more
Lars Vogel's tutorial
ProgrammerGuru article
Common intents
Intents are a way of telling Android what you want to do.
In other words, you describe your intention. 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 via an intent filter.
Following are 2 types of intents
1.Explicit Intents
used to call a specific component. When you know which component you want to launch and you do not want to give the user free control over which component to use. For example, you have an application that has 2 activities. Activity A and activity B. You want to launch activity B from activity A. In this case you define an explicit intent targeting activityB and then use it to directly call it.
2.Implicit Intents
used when you have an idea of what you want to do, but you do not know which component should be launched. Or if you want to give the user an option to choose between a list of components to use. 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 the component directly. For example, you have an application that uses the camera to take photos. One of the features of your application is that you give the user the possibility to send the photos he has taken. You do not know what kind of application the user has that can send photos, and you also want to give the user an option to choose which external application to use if he has more than one. In this case you would not use an explicit intent. Instead you should use an implicit intent that has its action set to ACTION_SEND and its data extra set to the URI of the photo.
An explicit intent is always delivered to its target, no matter what it contains; the filter is not consulted. But an implicit intent is delivered to a component only if it can pass through one of the component's filters
Intent Filters
If an Intents is send to the Android system, it will determine suitable applications for this Intents. If several components have been registered for this type of Intents, Android offers the user the choice to open one of them.
This determination is based on IntentFilters. An IntentFilters specifies the types of Intent that an activity, service, orBroadcast Receiver can respond to. An Intent Filter declares the capabilities of a component. It specifies what anactivity or service can do and what types of broadcasts a Receiver can handle. It allows the corresponding component to receive Intents of the declared type. IntentFilters are typically defined via the AndroidManifest.xml file. For BroadcastReceiver it is also possible to define them in coding. An IntentFilters is defined by its category, action and data filters. It can also contain additional metadata.
If a component does not define an Intent filter, it can only be called by explicit Intents.
Following are 2 ways to define a filter
1.Manifest file
If you define the intent filter in the manifest, your application does not have to be running to react to the intents defined in it’s filter. Android registers the filter when your application gets installed.
2.BroadCast Receiver
If you want your broadcast receiver to receive the intent only when your application is running. Then you should define your intent filter during run time (programatically). Keep in mind that this works for broadcast receivers only.
After writing a single activity, there comes a need to transition to another activity to perform another task either with or without information from the first activity.
Android platform allows transition by means of Intent Interface.
Words are taken from here: Using Intent Demo and i suggest you to go through this example because they also have provided a code file as well. so you can use it and easily understand the same.
Android Intent
Android Intent lets you navigate from one android activity to another. With examples, this tutorial also talks about various types of Android intents.
Android Intent can be defined as a simple message objects which is used to communicate from 1 activity to another.
Intents define intention of an Application . They are also used to transfer data between activities.
An Android Intent can be used to perform following 3 tasks :
Open another Activity or Service from the current Activity
Pass data between Activities and Services
Delegate responsibility to another application. For example, you can
use Intents to open the browser application to display a URL.
Intent can be broadly classified into 2 categories. There are no keywords for this category and just a broad classification of how android intents are used.
Explicit Android Intent
Explicit Android Intent is the Intent in which you explicitly define the component that needs to be called by Android System.
Intent MoveToNext = new Intent (getApplicationContext(), SecondActivity.class);
Implicit Android Intent
Implicit Android Intents is the intent where instead of defining the exact components, you define the action you want to perform. The decision to handle this action is left to the operating system. The OS decides which component is best to run for implicit intents.
Let us see an example:
Intent sendIntent = new Intent();
sendIntent.setAction(Intent.ACTION_SEND);
For more information you may visit below
http://developer.android.com/reference/android/content/Intent.html
According to their documentation:
An Intent is an object that provides runtime binding between separate components (such as two activities). The Intent represents an app’s "intent to do something." You can use intents for a wide variety of tasks, but most often they’re used to start another activity.
Here is the link with example:
http://developer.android.com/training/basics/firstapp/starting-activity.html#BuildIntent
As the document describes, in order to start an activity (you also need to understand what activity is) use the intent like below
/** Called when the user clicks the Send button */
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
An intent is an abstract description of an operation to be performed. It can be used with startActivity to launch an Activity, broadcastIntent to send it to any interested BroadcastReceiver components, and startService(Intent) or bindService(Intent, ServiceConnection, int) to communicate with a background Service.
For more details see these links :
1). http://developer.android.com/reference/android/content/Intent.html
2) http://developer.android.com/guide/topics/intents/intents-filters.html
3). http://www.vogella.de/articles/AndroidIntent/article.html
there are many more articles are available.
what is Intent ?
It is a kind of message or information that is passed to the components. It is used to launch an activity, display a web page, send sms, send email etc.
There are two types of intents in android:
Implicit Intent
Explicit Intent
Implicit intent is used to invoke the system components
Example
Intent i = newIntent(android.content.Intent.ACTION_VIEW,Uri.parse(“http://www.amazon.com”));
startActivity(i);
Explicit intent is used to invoke the activity class.
Example
Intent intent = newIntent (this, SecondActivity.class);
startActivity(intent);
you can read more
http://www.vogella.com/tutorials/AndroidIntent/article.html#intents_overview
http://developer.android.com/reference/android/content/Intent.html
An Intent is a class,that is bind the information for doing some actions.
example:passing data one activity to another actvity when user perform such actions in
present activity.
In a broad view, we can define Intent as
When one Activity wants to start another activity it creates an Object
called Intent that specifies which Activity it wants to start.
From the paper Deep Dive into Android IPC/Binder Framework atAndroid Builders Summit 2013 link
The intent is understood in some small but effective lines
Android supports a simple form of IPC(inter process communication) via intents
Intent messaging is a framework for asynchronous communication among Android components (activity, service, content providers, broadcast receiver )
Those components may run in the same or across different apps (i.e. processes)
Enables both point-to-point as well as publish subscribe messaging domains
The intent itself represents a message containing the description of the operation to be performed as well as data to be passed to the recipient(s).
From this thread a simple answer of android architect Dianne Hackborn states it as a data container which it actually is.
From android architecture point of view :
Intent is a data container that is used for inter process communication. It is built on top of the Binder from android architecture point of view.
An Android application can contain zero or more activities. When your application has more than one activity, you often need to navigate from one to another. In Android, you navigate between activities through what is known as an intent. You can pass some data to the activity which you want to start through intent, by using putExtra().
Intents are used to initiate another activity from one activity.It is basically used for several purposes such as sending data to another activity from one activity,and for triggering purposes.
They are basically of two types
Implicit intents.
Explicit intents.
As a beginner I know this much,I think this will give some basic idea about android intents
An intent is basically a way of passing data from one activity to other activity