Tasks and the back stack
A task is a collection of activities that users interact with when trying to do something in your app. These activities are arranged in a stack—the back stack—in the order in which each activity is opened.
Lifecycle of a task and its back stack
Back press behavior for root launcher activities
Root launcher activities are activities that declare an Intent filter with both ACTION_MAIN and CATEGORY_LAUNCHER. These activities are unique because they act as entry points into your app from the app launcher and are used to start a task.
- System behavior on Android 11 and lower The system finishes the activity.
- System behavior on Android 12 and higher
Background and foreground tasks
Multiple activity instances
Multi-window environments
In this regard, these are the principal
- taskAffinity
- launchMode
- allowTaskReparenting
- clearTaskOnLaunch
- alwaysRetainTaskState
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finishOnTaskLaunch And these are the principal intent flags that you can use:
- FLAG_ACTIVITY_NEW_TASK
- FLAG_ACTIVITY_CLEAR_TOP
- FLAG_ACTIVITY_SINGLE_TOP
Defining launch modes
Launch modes allow you to define how a new instance of an activity is associated with the current task.
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Using the manifest file
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Using Intent flags
Save key-value data
If you have a relatively small collection of key-values that you’d like to save, you should use the SharedPreferences APIs. A SharedPreferences object points to a file containing key-value pairs and provides simple methods to read and write them. Each SharedPreferences file is managed by the framework and can be private or shared.
Get a handle to shared preferences
- getSharedPreferences() — Use this if you need multiple shared preference files identified by name, which you specify with the first parameter. You can call this from any Context in your app.
- getPreferences() — Use this from an Activity if you need to use only one shared preference file for the activity. Because this retrieves a default shared preference file that belongs to the activity, you don’t need to supply a name.
Write to shared preferences
To write to a shared preferences file, create a SharedPreferences.Editor by calling edit() on your SharedPreferences.
Pass the keys and values you want to write with methods such as putInt() and putString().