Today we’ll take a look at one of the core components of all Android applications: intents. In this blog post, we’ll discuss what intents are, where they are used, and what pitfalls to consider. So let’s get started.
What Is an Intent?
You can think of an intent as a set of data describing an action a user wants to perform. Examples of intents include opening a gallery app, editing a document, picking a file or directory, adding a new calendar event, etc. Now let’s look at all the things contained in an intent.
Every intent can include an
action that generally describes which action you want to perform. Examples include
ACTION_VIEW to display a piece of data using the most appropriate applications,
ACTION_DIAL to open the dialer with a phone number prefilled, and many more.
Data and Type
Next up, you can add
data to your intent in the form of a
Uri should point to the data you want to perform the action on. For example, in the case of
data could be a phone number like
tel:012345. If you want to open a PDF document, it could be a file URI pointing to the document.
Furthermore, you can specify the
type to narrow down the scope of your intent. In most cases, Android will automatically determine the MIME type of your data based on the
Uri you specified for the
data in your intent. In cases where automated inference is not possible, you can manually specify the
type in addition to the
ℹ️ Pro Tip:
Intent#setData()will reset any
typethat was set, and
Intent#setType()will remove any
datathat was set. If you want to set both
type, you have to use
There is also the
component, which can be specified when you want to pass an intent to a specific class instead of letting the system automatically determine the best way to handle it. You can either set a
ComponentName if you want to specify an
Service that isn’t part of your application, or you just set the
Class if it is part of your application. If a
component is specified, this intent is considered an explicit intent, meaning it will always resolve to the specific
component that was set. On the other hand, if no
component was set, it is considered an implicit intent, meaning that the system will try to find the most appropriate
Service to handle it. In cases where there are multiple activities that could handle an intent, the system will show a dialog allowing the user to choose which one to use.
Finally, there are the
extras, which are where you can add any other information that doesn’t fit into either the
extras are just a
Bundle, and as such, you can store arbitrary primitive data or
Serializable objects in them. Keep in mind that you should never use the
extras bundle to pass around big amounts of data, as doing so will cause a
TransactionTooLargeException to be thrown.
Where Are Intents Used?
Now that we know the basics of what is contained in an intent, let’s look at where intents are used, starting with the most common use case: opening activities in your own application. To open an
Activity in your own application, you’ll use the
Intent(Context packageContext, Class<?> cls) constructor most of the time. This creates an explicit intent, meaning that this intent will only ever start the class specified in the constructor. Once you’ve created your intent, you will use
Context#startActivity() to start your
Another common use case for intents is to share data with other applications that are installed on a phone. To get an intent to share data, you can use
ShareCompat.IntentBuilder, which will prepare an intent for you. The intent you acquire from calling
createChooserIntent() will be an implicit intent, meaning that no
component was specified and any supported
Application on the device might be used.
You can even use intents to get data into your
Activity#startActivityForResult(), which allows the started
Activity to return a result to the starting
onActivityResult. This is used, for example, when you want to allow users to take a picture in your application but don’t want to provide your own camera integration. Google provides a great guide on how to do this, which you can find here.
Finally, among other things, intents are used both to start services and for broadcasts sent by the system and other applications.
To wrap up this blog post, let’s look at some common issues you might encounter when using intents.
Be Careful with Implicit Intents
Android’s system of using intents to communicate across applications is great because it allows you to integrate features provided by all kinds of different applications into yours. However, there is one problem with this: Not every user has the same set of applications installed.
If you are using an implicit intent to start an
Activity, you should always ensure there is an
Activity to handle the intent on the device. Otherwise, you will receive an
ActivityNotFoundException. To prevent this, you should use the
Intent#resolveActivity() method. This will tell you if there is an
Activity to handle your intent.
Don’t Overload Your Extras
As discussed before, you can put arbitrary
extras into your intent, but you should be careful what and how much you put in there. As mentioned earlier, the system will throw a
TransactionTooLargeException if you try to put too much data into an intent. To work around this, there are plenty of tools you can use.
If you are just trying to pass large data from one
Activity to another in your application, you could, for example, store the data in your application’s file directory and put just the path in the intent. On the other hand, if you are trying to pass large amounts of data to an external application, you should consider using a
ContentProvider, which will allow you to use the URIs it provides and pass them to any application you want.
In this blog post, we took a look at what an intent contains. We also looked at common use cases that require the use of an intent. Finally, we highlighted common pitfalls one might encounter when using intents. We hope that this helped you gain a deeper understanding of what intents are and where to use them.