What is an Android PendingIntent?

问题:

I am a newbie to Android. I read the Android Documentation but I still need some more clarification. Can anyone tell me what exactly a PendingIntent is?

回答1:

A PendingIntent is a token that you give to a foreign application (e.g. NotificationManager, AlarmManager, Home Screen AppWidgetManager, or other 3rd party applications), which allows the foreign application to use your application\'s permissions to execute a predefined piece of code.

If you give the foreign application an Intent, it will execute your Intent with its own permissions. But if you give the foreign application a PendingIntent, that application will execute your Intent using your application\'s permission.

回答2:

INTENT

Intents are the standard messaging mechanism in Android that expresses the user’s intention to perform some work. They allow you to interact with other components defined by you or by the Android operating system.

Example:

1. Broadcast a message
2. Start the camera
3. Start a service
4. Launch an activity
5. Display a web page or a list of contacts

6. Dial a phone number or answer a phone call

   They are used in both ways

1) by you to call a component

2)by the system to notify you of some event.

The logical workflow of creating an intent is usually as follows:

• Create the Intent
• b. Add Intent options-> Ex. what type of intent we are sending to the OS or any attributes associated with that intent, such as a text string or something being passed along with the intent
• c. RUN the Intent

Real Life Example: Let\'s say I wake up in the morning and I \"INTEND\" to go to the washroom. I will first have to THINK about going to the washroom, but that DOESN\'T really gets me to the washroom. I will then have to tell my brain to get out of bed first, then walk to the washroom, and then release, then go and wash my hands, then go and wipe my hands. Once I know where I\'m going I SEND the command to begin and my body takes action.

PENDINGINTENT

A PendingIntent specifies an action to take in the future. It lets you pass a future Intent to another application and allow that application to execute that Intent as if it had the same permissions as your application, whether or not your application is still around when the Intent is eventually invoked. It is a token that you give to a foreign application which allows the foreign application to use your application’s permissions to execute a predefined piece of code.

By giving a PendingIntent to another application, you are granting it the right to perform the operation you have specified as if the other application was yourself (with the same permissions and identity). As such, you should be careful about how you build the PendingIntent: often, for example, the base Intent you supply will have the component name explicitly set to one of your own components, to ensure it is ultimately sent there and nowhere else.

It is an Intent action that you want to perform but at a later time. Think of it a putting an Intent on ice. The reason it’s needed is because an Intent must be created and launched from a valid Context in your application, but there are certain cases where one is not available at the time you want to run the action because you are technically outside the application’s context (the two common examples are launching an Activity from a Notification or a BroadcastReceiver.By creating a PendingIntent you want to use to launch, say, an Activity while you have the Context to do so (from inside another Activity or Service)

Continuing from the real-life example: let\'s say I want to take a shower but I want to shower AFTER I brush my teeth and eat breakfast. So I know I won\'t be showering for at least 30-40 minutes. I still have in my head that I need to prepare my clothes, and then walk up the stairs back to the bathroom, then undress and then shower. However, this will not happen until 30-40 minutes have passed. Now I have a PENDING intent to shower. It is PENDING for 30-40 minutes.

That is pretty much the difference between a Pending Intent and a Regular Intent. In short:

Regular Intent -> DOES NOT REQUIRE PENDING INTENT TO BE MADE

Pending Intent -> REQUIRES A REGULAR INTENT TO BE CREATED

Intents are of two types- Explicit and Implicit

Explicit Intent: When your application is aware of which component to call to perform some action

Implicit Intent: When your application is not aware of which component can exactly perform your desired action. For Ex, If you simply say that you want to display a URL, the system decides what component will fulfill the intention.

For more better and clear idea about Intents. Vist below links

1. Slidenerd.com
2. Android Intent Tutorial
3. Some More

回答3:

A Pending Intent is a token you give to some app to perform an action on your apps\' behalf irrespective of whether your application process is alive or not.

I think the documentation is sufficiently detailed: Pending Intent docs.

Just think of use-cases for Pending Intents like (Broadcasting Intents, scheduling alarms) and the documentation will become clearer and meaningful.

回答4:

In my case, none of above answers nor google\'s official documentation helped me to grab the concept of PendingIntent class.

And then I found this video, Google I/O 2013, Beyond the Blue Dot session. In this video, ex-googler Jaikumar Ganesh explains what PendingIntent is, and that was the thing gave me the big picture of this.

Below is just transcription of above video (from 15:24).

So what\'s a pending intent?

It\'s a token that your app process will give to the location process, and the location process will use it to wake up your app when an event of interest happens. So this basically means that your app in the background doesn\'t have to be always running. When something of interest happens, we will wake you up. This saves a lot of battery.

This explanation becomes more clear with this snippet of code(which is included in the session\'s slide).

PendingIntent mIntent = PendingIntent.getService(...);

mLocationClient.requestLocationUpdates(locationRequest, mIntent);

public void onHandleIntent(Intent intent) {   
    String action = intent.getAction();   
    if (ACTION_LOCATION.equals(action)) {       
        Location location = intent.getParcelableExtra(...)   
    }
}

回答5:

Why PendingIntent is required ? I was thinking like

1. Why the receiving application itself cannot create the Intent or
2. Why we cannot use a simple Intent for the same purpose.

E.g.Intent bluetoothIntent= new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);

If I send bluetoothIntent to another application, which doesn\'t have permission android.permission.BLUETOOTH_ADMIN, that receiving application cannot enable Bluetooth with startActivity(bluetoothIntent).

The limitation is overcome using PendingIntent. With PendingIntent the receiving application, needn\'t have android.permission.BLUETOOTH_ADMIN for enabling Bluetooth. Source.

回答6:

Pending intent is an intent which will start at some point in the future. Normal intent starts immediately when it is passed to startActivity(Intent) or StartService(Intent).

回答7:

A future intent that other apps can use.
And here\'s an example for creating one:

Intent intent = new Intent(context, MainActivity.class);
PendingIntent pendIntent = PendingIntent.getActivity(context, 0, intent, 0);

回答8:

TAXI ANALOGY

Intent

Intents are typically used for starting Services. For example:

Intent intent = new Intent(CurrentClass.this, ServiceClass.class);
startService(intent);

This is like when you call for a taxi:

Myself = CurrentClass
Taxi Driver = ServiceClass

Pending Intent

You will need to use something like this:

Intent intent = new Intent(CurrentClass.this, ServiceClass.class);
PendingIntent pi = PendingIntent.getService(parameter, parameter, intent, parameter);
getDataFromThirdParty(parameter, parameter, pi, parameter);

Now this Third party will start the service acting on your behalf. A real life analogy is Uber or Lyft who are both taxi companies.

You send a request for a ride to Uber/Lyft. They will then go ahead and call one of their drivers on your behalf.

Therefore:

Uber/Lyft ------ ThirdParty which receives PendingIntent
Myself --------- Class calling PendingIntent
Taxi Driver ---- ServiceClass

回答9:

A PendingIntent is a token that you give to another application (e.g. Notification Manager, Alarm Manager or other 3rd party applications), which allows this other application to use the permissions of your application to execute a predefined piece of code. To perform a broadcast via a pending intent so get a PendingIntent via PendingIntent.getBroadcast(). To perform an activity via an pending intent you receive the activity via PendingIntent.getActivity().

回答10:

What is an Intent?

An Intent is a specific command in Android that allows you to send a command to the Android OS to do something specific. Think of it like an action that needs to take place. There are many actions that can be done such as sending an email, or attaching a photo to an email or even launching an application. The logical workflow of creating an intent is usually as follows: a. Create the Intent b. Add Intent options -> Ex. what type of intent we are sending to the OS or any attributes associated with that intent, such as a text string or something being passed along with the intent c. RUN the Intent

Real Life Example: Let\'s say I wake up in the morning and I \"INTEND\" to go to the washroom. I will first have to THINK about going to the washroom, but that DOESN\'T really get me to the washroom. I will then have to tell my brain to get out of bed first, then walk to the washroom, and then release, then go and wash my hands, then go and wipe my hands. Once I know where I\'m going I SEND the command to begin and my body takes action.

What is Pending Intents?

Continuing from the real life example, let\'s say I want to take a shower but I want to shower AFTER I brush my teeth and eat breakfast. So I know I won\'t be showering until at least 30-40 minutes. I still have in my head that I need to prepare my clothes, and then walk up the stairs back to the bathroom, then undress and then shower. However this will not happen until 30-40 minutes have passed. I now have a PENDING intent to shower. It is PENDING for 30-40 minutes.

That is pretty much the difference between a Pending Intent and a Regular Intent. Regular Intents can be created without a Pending Intent, however in order to create a Pending Intent you need to have a Regular Intent setup first.

回答11:

In an easy language,
1. A description of an Intent and Target action to perform. First you have to create an intent and then you have to pass an specific java class which you want to execute, to the Intent.
2. You can call those java class which is your class action class by PendingIntent.getActivity, PendingIntent.getActivities(Context, int, Intent[], int), PendingIntent.getBroadcast(Context, int, Intent, int), and PendingIntent.getService(Context, int, Intent, int); Here you see that Intent which is comes from the step 1
3. You should keep in mind that...By giving a PendingIntent to another application, you are granting it the right to perform the operation you have specified.

That is what I learned after a long reading.

回答12:

A PendingIntent wraps the general Intent with a token that you give to foreign app to execute with your permission. For eg:

The notification of your music app can\'t play/pause the music if you didn\'t give the PendingIntent to send broadcast because your music app has READ_EXTERNAL_STORAGE permission which the notification app doesn\'t. Notification is a system service (so it\'s a foreign app).

回答13:

PendingIntent is basically an object that wraps another Intent object. Then it can be passed to a foreign application where you’re granting that app the right to perform the operation, i.e., execute the intent as if it were executed from your own app’s process (same permission and identity). For security reasons you should always pass explicit intents to a PendingIntent rather than being implicit.

 PendingIntent aPendingIntent = PendingIntent.getService(Context, 0, aIntent,
                    PendingIntent.FLAG_CANCEL_CURRENT);

回答14:

As its name suggest .. PendingIntent

you can pend(do it after some time) it . It work as the other intent ..it is a way of giving your task to some other app to perform on your behalf.

回答15:

A Pending Intent specifies an action to take in the future. It lets you pass a future Intent to another application and allow that application to execute that Intent as if it had the same permissions as your application, whether or not your application is still around when the Intent is eventually invoked.

It is a token that you give to a foreign application which allows the foreign application to use your application’s permissions to execute a predefined piece of code.

If you give the foreign application an Intent, and that application sends/broadcasts the Intent you gave, they will execute the Intent with their own permissions. But if you instead give the foreign application a Pending Intent you created using your own permission, that application will execute the contained Intent using your application’s permission.

To perform a broadcast via a pending intent so get a PendingIntent via PendingIntent.getBroadcast(). To perform an activity via an pending intent you receive the activity via PendingIntent.getActivity().

It is an Intent action that you want to perform, but at a later time. Think of it a putting an Intent on ice. The reason it’s needed is because an Intent must be created and launched from a valid Context in your application, but there are certain cases where one is not available at the time you want to run the action because you are technically outside the application’s context (the two common examples are launching an Activity from a Notification or a BroadcastReceiver.

By creating a PendingIntent you want to use to launch, say, an Activity while you have the Context to do so (from inside another Activity or Service) you can pass that object around to something external in order for it to launch part of your application on your behalf.

A PendingIntent provides a means for applications to work, even after their process exits. Its important to note that even after the application that created the PendingIntent has been killed, that Intent can still run. A description of an Intent and target action to perform with it. Instances of this class are created with getActivity(Context, int, Intent, int), getBroadcast(Context, int, Intent, int), getService (Context, int, Intent, int); the returned object can be handed to other applications so that they can perform the action you described on your behalf at a later time.

By giving a PendingIntent to another application, you are granting it the right to perform the operation you have specified as if the other application was yourself (with the same permissions and identity). As such, you should be careful about how you build the PendingIntent: often, for example, the base Intent you supply will have the component name explicitly set to one of your own components, to ensure it is ultimately sent there and nowhere else.

A PendingIntent itself is simply a reference to a token maintained by the system describing the original data used to retrieve it. This means that, even if its owning application’s process is killed, the PendingIntent itself will remain usable from other processes that have been given it. If the creating application later re-retrieves the same kind of PendingIntent (same operation, same Intent action, data, categories, and components, and same flags), it will receive a PendingIntent representing the same token if that is still valid, and can thus call cancel() to remove it.

回答16:

Pending Intent is an intent who provides all permission to other application to do a particular works. When the main activity is destroyed, Android OS takes back the permission from it.