How do intents work in android

Cloud Computing. Data Science. Angular 7. Machine Learning. Data Structures. Operating System. Computer Network. Compiler Design. Computer Organization. Discrete Mathematics. Ethical Hacking.

Computer Graphics. Software Engineering. The request code is an integer that identifies the request and can be used to differentiate between results when you process the return data. For example, if you launch one activity to take a photo and another to pick a photo from a gallery, you'll need different request codes to identify which request the returned data belongs to.

Use a different integer for each code. The response data from the launched activity back to the originating activity is sent in an intent, either in the data or the extras. You construct this return intent and put the data into it in much the same way you do for the sending intent.

Typically your launched activity will have an onClick or other user input callback method in which you process the user's action and close the activity.

This is also where you construct the response. Return result intents do not need a class or component name to end up in the right place. The Android system directs the response back to the originating activity for you. Add data or extras to the intent the same way you did with the original intent.

You may need to define keys for the return intent extras at the start of your class. Then put your return data into the intent as usual. Now that the launched activity has sent data back to the originating activity with an intent, that first activity must handle that data. To handle returned data in the originating activity, implement the onActivityResult callback method.

Here is a simple example. The three arguments to the onActivityResult contain all the information you need to handle the return data. The example method shown above shows the typical logic for handling the request and response codes. Inside the body of those tests you extract the return information out of the intent.

Use getData to get the intent data, or getExtra to retrieve values out of the intent extras with a specific key. Any app of any complexity that you build will include multiple activities, both designed and implemented by you, and potentially in other apps as well. As your users move around your app and between activities, consistent navigation becomes more important to the app's user experience.

Few things frustrate users more than basic navigation that behaves in inconsistent and unexpected ways. Thoughtfully designing your app's navigation will make using your app predictable and reliable for your users.

Back navigation allows your users to return to the previous activity by tapping the device back button. Back navigation is also called temporal navigation because the back button navigates the history of recently viewed screens, in reverse chronological order. The back stack is the set of activities that the user has visited and that can be returned to by the user with the back button. Each time a new activity starts, it is pushed onto the back stack and takes user focus.

The previous activity is stopped but is still available in the back stack. The back stack operates on a "last in, first out" mechanism, so when the user is done with the current activity and presses the Back button, that activity is popped from the stack and destroyed and the previous activity resumes. Because an app can start activities both inside and outside a single app, the back stack contains all the activities that have been launched by the user in reverse order.

Each time the user presses the Back button, each activity in the stack is popped off to reveal the previous one, until the user returns to the Home screen. Android provides a back stack for each task. A task is an organizing concept for all the activities the user interacts with when performing an operation, whether they are inside your app or across multiple apps. Most tasks start from the Android home screen, and tapping an app icon starts a task and a new back stack for that app.

If the user uses an app for a while, taps home, and starts a new app, that new app launches in its own task and has its own back stack. If the user returns to the first app, that first task's back stack returns. Navigating with the back button only returns to the activities in the current task, not for all tasks running on the device. Android enables the user to navigate between tasks with the overview or recent tasks screen, accessible with the square button on lower right corner of the device.

In most cases you don't have to worry about managing either tasks or the back stack for your app—the system keeps track of these things for you, and the back button is always available on the device. There may, however, be times where you may want to override the default behavior for tasks or for the back stack. For example, if your screen contains an embedded web browser where users can navigate between web pages, you may wish to use the browser's default back behavior when users press the device's Back button, rather than returning to the previous activity.

You may also need to change the default behavior for your app in other special cases such as with notifications or widgets, where activities deep within your app may be launched as their own tasks, with no back stack at all. 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. 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:. 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.

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:. 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.

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. 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. 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. 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. In many cases the user has a preferred app for a given task, and they will select the option to always use that app for that task. However, if multiple apps can respond to the Intent and the user might want to use a different app each time, you can choose to explicitly show a chooser dialog every time. To show the chooser, you create a wrapper Intent for your implicit Intent with the createChooser method, and then resolve and call startActivity with that wrapper Intent.

The createChooser method also requires a string argument for the title that appears on the chooser. You can specify the title with a string resource as you would any other string. If you want an Activity in your app to respond to an implicit Intent from your own app or other apps , declare one or more Intent filters in the AndroidManifest.

Each Intent filter specifies the type of Intent it accepts based on the action, data, and category for the Intent. The system will deliver an implicit Intent to your app component only if that Intent can pass through one of your Intent filters. Once your Activity is successfully launched with an implicit Intent , you can handle that Intent and its data the same way you did an explicit Intent , by:.

The Android system matches an implicit intent with an activity or other app component only if the fields in the Intent object match the Intent filters for that component. An Intent filter may contain the following elements, which correspond to the fields in the Intent object described above:. Only the main activity for your app should have this Intent filter. Here's another example for an implicit Intent that shares a bit of text.

This Intent filter matches the implicit Intent example from the previous section:. You can specify more than one action, data, or category for the same Intent filter, or have multiple Intent filters per Activity to handle each different kind of Intent. The Android system tests an implicit Intent against an Intent filter by comparing the parts of that Intent to each of the three Intent filter elements action, category, and data. The Intent must pass all three tests or the Android system won't deliver the Intent to the component.

However, because a component may have multiple Intent filters, an Intent that does not pass through one of a component's filters might make it through on another filter. The action is defined in the name attribute, and consists of the string "android.

To get through this filter, the action specified in the incoming Intent object must match at least one of the actions. You must include at least one Intent action for an incoming implicit Intent to match. The category is defined in the name attribute, and consists of the string "android. Note that any Activity that you want to accept an implicit Intent must include the android. This category is applied to all implicit Intent objects by the Android system.

Share actions are an easy way for users to share items in your app with social networks and other apps. IntentBuilder helper class to easily implement sharing in your app. With the ShareCompat. IntentBuilder class you do not need to create or send an implicit Intent for the share action.

Use the methods in ShareCompat. IntentBuilder to indicate the data you want to share as well as any additional information. Start with the from method to create a new Intent builder, add other methods to add more data, and end with the startChooser method to create and send the Intent.