Download after onCreate android

Doing the right work at the right time and handling transitions properly make your app more robust and performant. For example, good implementation of the lifecycle callbacks can help ensure that your app avoids:.

This document explains the activity lifecycle in detail. The document begins by describing the lifecycle paradigm. Next, it explains each of the callbacks: what happens internally while they execute, and what you should implement during them. Last, it discusses several topics related to transitions between activity states. To learn how to architect a robust, production-quality app using activities in combination with architecture components, see Guide to App Architecture.

To navigate transitions between stages of the activity lifecycle, the Activity class provides a core set of six callbacks: onCreate , onStart , onResume , onPause , onStop , and onDestroy. The system invokes each of these callbacks as an activity enters a new state.

Figure 1. A simplified illustration of the activity lifecycle. As the user begins to leave the activity, the system calls methods to dismantle the activity. In some cases, this dismantlement is only partial; the activity still resides in memory such as when the user switches to another app , and can still come back to the foreground. If the user returns to that activity, the activity resumes from where the user left off.

With a few exceptions, apps are restricted from starting activities when running in the background. Activity state and ejection from memory provides more information on the relationship between state and vulnerability to ejection. Depending on the complexity of your activity, you probably don't need to implement all the lifecycle methods.

However, it's important that you understand each one and implement those that ensure your app behaves the way users expect. The next section of this document provides detail on the callbacks that you use to handle transitions between states. This section provides conceptual and implementation information about the callback methods used during the activity lifecycle.

Some actions, such as calling setContentView , belong in the activity lifecycle methods themselves. However, the code implementing the actions of a dependent component should be placed in the component itself. 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. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How can I know that OnResume comes after onCreate?

Ask Question. Asked 10 years, 2 months ago. Active 2 years, 6 months ago. Viewed 14k times. I have few activities and from one activity I open another and that go back to the first one Improve this question. Lukap Lukap Why not add a boolean yourself, you can set it to true in the onCreate method, evaluate in onResume , and set it to false there. If u want you can call onResume in your onCreate. Perform what you want if flag is set in onResume method.

But why don't you want the flag? It is the easiest and simplest solution. Because I have really nasty program with a lot of threads, and I do not want to synchronize the flag to be thread safe cause I causes it acts sluggish I do not why is that. It is probably I do some stupid mistake in synchronization — Lukap.

Show 1 more comment. Active Oldest Votes. However, activity's onCreate might not finished until onActivityCreated? Is these any chance of crash in onCreateView for accessing view hierarchy? One thing to note at least with the AppCompatActivity is that when the activity is recreated e. This can be a problem if you are using something like Dagger and need to access something in the parent activity that is injected.

One solution to this is to put the code in onActivityCreated which is called always called of onCreate is called. Is it save to assume that the activity's onCreate has finished, once the onCreateView of it's Fragments is called? Show 5 more comments. Comic Sans is necessary for things like this — Kartik Chugh. It's the first time I see 3 different fonts in the same diagram, and somehow my life feels complete now. When exactly could a fragment restart?

How come the fragment is not re-created once it's process is dead? AFAIK, only the task state preserved as a bundle and it's re-created the app is brought to foreground again. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.

Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. Thank you. Microsoft makes no warranties, express or implied, with respect to the information provided here. If the activity is being re-initialized after previously being shut down then this Bundle contains the data it most recently supplied in onSaveInstanceState.