Android what should be in ondestroy

To achieve this, you must make the dependent component lifecycle-aware. See Handling Lifecycles with Lifecycle-Aware Components to learn how to make your dependent components lifecycle-aware. You must implement this callback, which fires when the system first creates the activity. On activity creation, the activity enters the Created state.

In the onCreate method, you perform basic application startup logic that should happen only once for the entire life of the activity. For example, your implementation of onCreate might bind data to lists, associate the activity with a ViewModel , and instantiate some class-scope variables.

This method receives the parameter savedInstanceState , which is a Bundle object containing the activity's previously saved state. If the activity has never existed before, the value of the Bundle object is null. The method annotated with OnLifecycleEvent will be called so your lifecycle-aware component can perform any setup code it needs for the created state.

The following example of the onCreate method shows fundamental setup for the activity, such as declaring the user interface defined in an XML layout file , defining member variables, and configuring some of the UI. As an alternative to defining the XML file and passing it to setContentView , you can create new View objects in your activity code and build a view hierarchy by inserting new View s into a ViewGroup.

You then use that layout by passing the root ViewGroup to setContentView. For more information about creating a user interface, see the User Interface documentation. Your activity does not reside in the Created state.

After the onCreate method finishes execution, the activity enters the Started state, and the system calls the onStart and onResume methods in quick succession. The next section explains the onStart callback. When the activity enters the Started state, the system invokes this callback. The onStart call makes the activity visible to the user, as the app prepares for the activity to enter the foreground and become interactive.

For example, this method is where the app initializes the code that maintains the UI. The onStart method completes very quickly and, as with the Created state, the activity does not stay resident in the Started state.

Once this callback finishes, the activity enters the Resumed state, and the system invokes the onResume method. When the activity enters the Resumed state, it comes to the foreground, and then the system invokes the onResume callback. This is the state in which the app interacts with the user. The app stays in this state until something happens to take focus away from the app. This is where the lifecycle components can enable any functionality that needs to run while the component is visible and in the foreground, such as starting a camera preview.

When an interruptive event occurs, the activity enters the Paused state, and the system invokes the onPause callback. If the activity returns to the Resumed state from the Paused state, the system once again calls onResume method. For this reason, you should implement onResume to initialize components that you release during onPause , and perform any other initializations that must occur each time the activity enters the Resumed state.

In multi-window mode, however, your activity may be fully visible even when it is in the Paused state. For example, when the user is in multi-window mode and taps the other window that does not contain your activity, your activity will move to the Paused state.

If you want to keep the camera active while the activity is Paused but visible e. Note, however, that having the camera active while your activity is Paused may deny access to the camera to another Resumed app in multi-window mode. Sometimes it may be necessary to keep the camera active while your activity is Paused, but it may actually degrade the overall user experience if you do. Think carefully about where in the lifecycle it is more appropriate to take control of shared system resources in the context of multi-window.

To learn more about supporting multi-window mode, see Multi-Window Support. Regardless of which build-up event you choose to perform an initialization operation in, make sure to use the corresponding lifecycle event to release the resource. Note, the code snippet above places camera initialization code in a lifecycle aware component. You can instead put this code directly into the activity lifecycle callbacks such as onStart and onStop but this isn't recommended.

Adding this logic into an independent, lifecycle-aware component allows you to reuse the component across multiple activities without having to duplicate code. See Handling Lifecycles with Lifecycle-Aware Components to learn how to create a lifecycle-aware component.

The system calls this method as the first indication that the user is leaving your activity though it does not always mean the activity is being destroyed ; it indicates that the activity is no longer in the foreground though it may still be visible if the user is in multi-window mode. Use the onPause method to pause or adjust operations that should not continue or should continue in moderation while the Activity is in the Paused state, and that you expect to resume shortly. There are several reasons why an activity may enter this state.

For example:. This is where the lifecycle components can stop any functionality that does not need to run while the component is not in the foreground, such as stopping a camera preview. You can also use the onPause method to release system resources, handles to sensors like GPS , or any resources that may affect battery life while your activity is paused and the user does not need them. However, as mentioned above in the onResume section, a Paused activity may still be fully visible if in multi-window mode.

As such, you should consider using onStop instead of onPause to fully release or adjust UI-related resources and operations to better support multi-window mode. As previously mentioned, see Handling Lifecycles with Lifecycle-Aware Components to learn how to create a lifecycle-aware component. For this reason, you should not use onPause to save application or user data, make network calls, or execute database transactions; such work may not complete before the method completes.

Instead, you should perform heavy-load shutdown operations during onStop. For more information about suitable operations to perform during onStop , see onStop. For more information about saving data, see Saving and restoring activity state.

Completion of the onPause method does not mean that the activity leaves the Paused state. Rather, the activity remains in this state until either the activity resumes or becomes completely invisible to the user. If the activity resumes, the system once again invokes the onResume callback. If the activity returns from the Paused state to the Resumed state, the system keeps the Activity instance resident in memory, recalling that instance when the system invokes onResume.

If the activity becomes completely invisible, the system calls onStop. The next section discusses the onStop callback. When your activity is no longer visible to the user, it has entered the Stopped state, and the system invokes the onStop callback. This may occur, for example, when a newly launched activity covers the entire screen. The system may also call onStop when the activity has finished running, and is about to be terminated.

This is where the lifecycle components can stop any functionality that does not need to run while the component is not visible on the screen. In the onStop method, the app should release or adjust resources that are not needed while the app is not visible to the user.

For example, your app might pause animations or switch from fine-grained to coarse-grained location updates. Using onStop instead of onPause ensures that UI-related work continues, even when the user is viewing your activity in multi-window mode.

You should also use onStop to perform relatively CPU-intensive shutdown operations. For example, if you can't find a more opportune time to save information to a database, you might do so during onStop.

The following example shows an implementation of onStop that saves the contents of a draft note to persistent storage:. Note, the code sample above uses SQLite directly. You should instead use Room, a persistence library that provides an abstraction layer over SQLite. To learn more about the benefits of using Room, and how to implement Room in your app, see the Room Persistence Library guide.

When your activity enters the Stopped state, the Activity object is kept resident in memory: It maintains all state and member information, but is not attached to the window manager. When the activity resumes, the activity recalls this information.

The system also keeps track of the current state for each View object in the layout, so if the user entered text into an EditText widget, that content is retained so you don't need to save and restore it. Note: Once your activity is stopped, the system might destroy the process that contains the activity if the system needs to recover memory. Even if the system destroys the process while the activity is stopped, the system still retains the state of the View objects such as text in an EditText widget in a Bundle a blob of key-value pairs and restores them if the user navigates back to the activity.

For more information about restoring an activity to which a user returns, see Saving and restoring activity state. From the Stopped state, the activity either comes back to interact with the user, or the activity is finished running and goes away.

If the activity comes back, the system invokes onRestart. If the Activity is finished running, the system calls onDestroy.

The next section explains the onDestroy callback. This is where the lifecycle components can clean up anything it needs to before the Activity is destroyed. Instead of putting logic in your Activity to determine why it is being destroyed you should use a ViewModel object to contain the relevant view data for your Activity. If the Activity is going to be recreated due to a configuration change the ViewModel does not have to do anything since it will be preserved and given to the next Activity instance.

If the Activity is not going to be recreated then the ViewModel will have the onCleared method called where it can clean up any data it needs to before being destroyed. You can distinguish between these two scenarios with the isFinishing method. If the activity is finishing, onDestroy is the final lifecycle callback the activity receives. If onDestroy is called as the result of a configuration change, the system immediately creates a new activity instance and then calls onCreate on that new instance in the new configuration.

The onDestroy callback should release all resources that have not yet been released by earlier callbacks such as onStop. The system kills processes when it needs to free up RAM; the likelihood of the system killing a given process depends on the state of the process at the time.

Process state, in turn, depends on the state of the activity running in the process. Dismiss method. As an example, the following code snippet will release the camera, as the Activity cannot make use of it while paused:. OnStop is called when the activity is no longer visible to the user. This happens when one of the following occurs:.

OnStop may not always be called in low-memory situations, such as when Android is starved for resources and cannot properly background the Activity. For this reason, it is best not to rely on OnStop getting called when preparing an Activity for destruction.

The next lifecycle methods that may be called after this one will be OnDestroy if the Activity is going away, or OnRestart if the Activity is coming back to interact with the user. OnDestroy is the final method that is called on an Activity instance before it's destroyed and completely removed from memory. In extreme situations Android may kill the application process that is hosting the Activity, which will result in OnDestroy not being invoked.

Most Activities will not implement this method because most clean up and shut down has been done in the OnPause and OnStop methods. The OnDestroy method is typically overridden to clean up long running tasks that might leak resources. An example of this might be background threads that were started in OnCreate. OnRestart is called after your activity has been stopped, prior to it being started again.

A good example of this would be when the user presses the home button while on an activity in the application. When this happens OnPause and then OnStop methods are called, and the Activity is moved to the background but is not destroyed. If the user were then to restore the application by using the task manager or a similar application, Android will call the OnRestart method of the activity. There are no general guidelines for what kind of logic should be implemented in OnRestart.

This is because OnStart is always invoked regardless of whether the Activity is being created or being restarted, so any resources required by the Activity should be initialized in OnStart , rather than OnRestart. Many Android devices have two distinct buttons: a "Back" button and a "Home" button.

An example of this can be seen in the following screenshot of Android 4. There is a subtle difference between the two buttons, even though they appear to have the same effect of putting an application in the background. When a user clicks the Back button, they are telling Android that they are done with the activity. Android will destroy the Activity.

In contrast, when the user clicks the Home button the activity is merely placed into the background — Android will not kill the activity. When an Activity is stopped or destroyed the system provides an opportunity to save the state of the Activity for later rehydration. This saved state is referred to as instance state.

Android provides three options for storing instance state during the Activity lifecycle:. Storing primitive values in a Dictionary known as a Bundle that Android will use to save state. Creating a custom class that will hold complex values such as bitmaps.

Android will use this custom class to save state. Circumventing the configuration change lifecycle and assuming complete responsibility for maintaining state in the activity. Recall that when an Activity is created that the OnCreate method is passed a bundle as a parameter, this bundle can be used to restore the instance state. An Activity provides methods to help with saving and retrieving the instance state in the Bundle:. OnRestoreInstanceState — This is called after the OnCreate method is finished, and provides another opportunity for an Activity to restore its state after initialization is complete.

OnSaveInstanceState will be called as the Activity is being stopped. It will receive a bundle parameter that the Activity can store its state in. The user just leaves: this is the only event that you will be aware of onPause in an activity. You should design your app so that it fits this lifecycle. Typically, you should save any changes immediately but asynchronously, so that the UI doesn't hang.

This is much better than saving changes in onPause because if something bad happens before the app is paused the app crashes, the user runs out of battery , all data was already saved properly. Basically, there's never a guarantee that onDestroy will be called, and in some cases processes such as your app will be killed directly, bypassing the method call anyway.

The second parameter is not a position. It is the ID of a layout resource, one that is used by default for the rows created by the ArrayAdapter. You can tell that by reading the JavaDocs for the constructor that you are calling. In Java, the "default constructor" is a zero-argument constructor. Every constructor in Java needs to chain to a superclass constructor.

If the superclass has a zero-argument "default" constructor, Java will chain to it automatically. If the superclass does not have a zero-argument constructor, you need to chain to a superclass constructor manually.