Activities are a fundamental building block of Android applications and they can exist in a number of different states. The activity lifecycle begins with instantiation and ends with destruction, and includes many states in between. When an activity changes state, the appropriate lifecycle event method is called, notifying the activity of the impending state change and allowing it to execute code to adapt to that change. This article examines the lifecycle of activities and explains the responsibility that an activity has during each of these state changes to be part of a well-behaved, reliable application.
Activities are an unusual programming concept specific to Android. In traditional application development there is usually a static main method, which is executed to launch the application. With Android, however, things are different; Android applications can be launched via any registered activity within an application. In practice, most applications will only have a specific activity that is specified as the application entry point.
However, if an application crashes, or is terminated by the OS, the OS can try to restart the application at the last open activity or anywhere else within the previous activity stack. Additionally, the OS may pause activities when they're not active, and reclaim them if it is low on memory.
Careful consideration must be made to allow the application to correctly restore its state in the event that an activity is restarted, especially if that activity depends on data from previous activities. The activity lifecycle is implemented as a collection of methods the OS calls throughout the lifecycle of an activity.
These methods allow developers to implement the functionality that is necessary to satisfy the state and resource management requirements of their applications. It is extremely important for the application developer to analyze the requirements of each activity to determine which methods exposed by the activity lifecycle need to be implemented.
Failure to do this can result in application instability, crashes, resource bloat, and possibly even underlying OS instability. This section also includes a walkthrough that provide practical examples on how to efficiently save state during the Activity lifecycle.
By the end of this chapter you should have an understanding of the Activity lifecycle and how to support it in an Android application. The Android activity lifecycle comprises a collection of methods exposed within the Activity class that provide the developer with a resource management framework. This framework allows developers to meet the unique state management requirements of each activity within an application and properly handle resource management. The Android OS arbitrates Activities based on their state.
This helps Android identify activities that are no longer in use, allowing the OS to reclaim memory and resources. The following diagram illustrates the states an Activity can go through during its lifetime:. Active or Running — Activities are considered active or running if they are in the foreground, also known as the top of the activity stack. This is considered the highest priority activity in Android, and as such will only be killed by the OS in extreme situations, such as if the activity tries to use more memory than is available on the device as this could cause the UI to become unresponsive.
Paused — When the device goes to sleep, or an activity is still visible but partially hidden by a new, non-full-sized or transparent activity, the activity is considered paused. Paused activities are still alive, that is, they maintain all state and member information, and remain attached to the window manager.
Xamarin Android: Create Android App One Activity To Another Activity Passing Value
Stopped activities still try to retain their state and member information for as long as possible, but stopped activities are considered to be the lowest priority of the three states and, as such, the OS will kill activities in this state first to satisfy the resource requirements of higher priority activities. Restarted — It is possible for an activity that is anywhere from paused to stopped in the lifecycle to be removed from memory by Android.
If the user navigates back to the activity it must be restarted, restored to its previously saved state, and then displayed to the user. To make matters more complicated, Android throws one more wrench in the mix called Configuration Changes. Configuration changes still cause the same Activity State changes that would occur during stopping and restarting an activity. However, in order to make sure that an application feels responsive and performs well during configuration changes, it's important that they are handled as quickly as possible.Xamarin Android Lesson2 - Input, Activities, and Intents
Because of this, Android has a specific API that can be used to persist state during configuration changes. We'll cover this later in the Managing State Throughout the Lifecycle section.
Android framework provide a powerful model for managing the state of activities within an application. When an activity's state is changing, the activity is notified by the OS, which calls specific methods on that activity.
The following diagram illustrates these methods in relation to the Activity Lifecycle:. As a developer, you can handle state changes by overriding these methods within an activity. It's important to note, however, that all lifecycle methods are called on the UI thread and will block the OS from performing the next piece of UI work, such as hiding the current activity, displaying a new activity, etc.
As such, code in these methods should be as brief as possible to make an application feel well performing.Activity lifecycle is quite more complex. As you know Activity is single page in the Android app where user can perform interaction with it. As you can see there is specific flow of Activity lifecycle. In the mobile application you have of course methods in each Activity class that handle specific lifecycle fragment:.
The entire lifetime of an activity happens between the first call to onCreate Bundle through to a single final call to onDestroy. An activity will do all setup of "global" state in onCreateand release all remaining resources in onDestroy. For example, if it has a thread running in the background to download data from the network, it may create that thread in onCreate and then stop the thread in onDestroy. The visible lifetime of an activity happens between a call to onStart until a corresponding call to onStop.
Subscribe to RSS
During this time the user can see the activity on-screen, though it may not be in the foreground and interacting with the user. Between these two methods you can maintain resources that are needed to show the activity to the user. For example, you can register a BroadcastReceiver in onStart to monitor for changes that impact your UI, and unregister it in onStop when the user no longer sees what you are displaying.
The onStart and onStop methods can be called multiple times, as the activity becomes visible and hidden to the user. The foreground lifetime of an activity happens between a call to onResume until a corresponding call to onPause. During this time the activity is in front of all other activities and interacting with the user.
An activity can frequently go between the resumed and paused states -- for example when the device goes to sleep, when an activity result is delivered, when a new intent is delivered -- so the code in these methods should be fairly lightweight. Download Xamarin. Android PDF Xamarin. Android Getting started with Xamarin.
Android App lifecycle - Xamarin. Android - Bluetooth communication Xamarin. Android - How to create a toolbar.Android application. Android solution. Android includes several templates for creating projects, including:.
In the previous section, we created a simple Xamarin. Android project. In doing so, Xamarin. Android generated a variety of things for us. These items are summarized in the table below:. The project template also created a class called Activity1 in the file MainActivity. An Activity is a class that models a destination where a user can perform some action while using an app, typically via a user interface.
Conceptually, an activity can be thought of as being mapped to an application screen. NETin that every activity has a lifecycle associated with it. An Activity contains methods to be called at certain points in the lifecycle.
Understand the Activity Lifecycle
These methods can also be overridden. For example, the Activity subclass created by the project template overrides the OnCreate method, which is called after an Activity first starts.
This will let you see a good example of the running app and it will help you become familiar with the process of deploying and launching in the emulator. Select the emulator in the list and choose Start Emulator. Selecting Start emulator image in this dialog will open a list of available emulators:. Android launches the emulator. After it starts up, the emulator will appear in the Running devices list as shown below:.
After the emulator starts up, slide the lock button to the right to show the Android home screen:. Back in the Select Device dialog, we can now build and deploy our app by selecting the emulator in the list, and then clicking OK. The first time a Xamarin. Android application is installed, the Xamarin. Android shared runtime will be installed, followed by the application. Android deploys the app to the emulator, and then launches it.
The default app created from the template consists of a Button. Clicking the button increments a counter, as shown below:. Clicking the button will change the text of the TextView. Here is a screenshot that shows the application running in the emulator.
After an Activity starts, its OnCreate method is called.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. Want to read about the creation, check out my in-depth blog post.
Build Status:. This plugin provides base functionality for Plugins for Xamarin to gain access to the application's main Activity. When the plugin is installed, follow the below steps to initialize in your project.
There are two ways to initialize this:. The benefit of adding it at the Application level is to get the first events for the application. Call CrossCurrentActivity. Current from your Android project to gain access to APIs. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
Android apps and library creators to easily get access to the current Activity. Since then it has been the core of many of my plugins and has been installed overtimes from NuGet! Times change and it is time for an update to this near perfect library. If you have ever used this library or had it as a dependency then you will remember a magical MainApplication. This laid down everything that the plugin needed to track the current Activity state with IActivityLifecycleCallbacks.
While this was a really simple use case it sometimes ran into issues when developers already had a custom Application class and more over now that Package References are the default for Visual Studio this file no longer gets added to the project.
Thanks to the mastermind Jon Dick who I am working with on some new libraries and pointed out that instead of having developers write their own custom Application or rely on a magical file that I could just create my own IActivityLifecycleCallbacks and have a simple Init call.
On top of that I could preserve backwards compatibility with any installations of 1. How can this be? Well I created my own lifecycle listener and now there is just a tiny bit of setup inside of your existing custom application or main activity:.
Add a new C class file in you project called "MainApplication. Override the OnCreate method and call the Init method:. In version 1. You can grab a copy of version 2. Throughout the month of April I will be updating all of my plugins to use this new version. I am really excited for it and hope that you find it useful. If you are building a library that depends on CurrentActivity please update to version 2. Checkout my monthly newsletter that you should subscribe to!
Xamarin Xamarin. Automatic Tracking Thanks to the mastermind Jon Dick who I am working with on some new libraries and pointed out that instead of having developers write their own custom Application or rely on a magical file that I could just create my own IActivityLifecycleCallbacks and have a simple Init call. Init this, bundle. Android Xamarin Plugins. Tags Xamarin Xamarin. Author James Montemagno. My Podcasts Checkout my monthly newsletter that you should subscribe to!This directory holds the sample projects from the Creating Services guides for Xamarin.
There are multiple solutions in the subdirectories of this project. Each solution is meant to be a stand alone solution that focus on a specific topic. BoundServicesDemo — Example of creating a bound service with Xamarin. ForegroundServiceDemo — A sample demonstrating a foreground service. StartedServicesDemo — An example of creating a started service in Xamarin.
It demonstates how perform one-way and two-way IPC calls between an Activty and a Service running in it's own process. Ensure that the MessengerService project is installed on the device before the MeessengerClient project. If the MessengerClient is inadvertently installed first, it will be necessary to uninstall it, install the MessengerService app, and then reinstall the MessengerClient project. Skip to content.
Branch: master. Create new file Find file History. Latest commit Fetching latest commit…. Authors Tom Opgenorth toopge microsoft. You signed in with another tab or window.
Reload to refresh your session. You signed out in another tab or window. Fix links to docs.
Jul 24, Aug 3, Change MD formatting. Apr 25, Comment 0. Android does not have the same structure than a Windows or Windows Phone app. Android has Activities. Activities are the key classes of Android were all actions take place. In Android, the starting point is an Activity. The Activity needs to be declared as the starting point.
Think of this as your MainPage. Every Activity has its own OnCreate event, where you can put all your starting, button handlers, stylings etc. But an Activity still has more. The Context is often needed in an Android application and allows your code to be run within an Activity. Without Context, often code does not get accepted by the IDE or makes your code getting ignored while running the app.
Luckily, all methods that I used so far have been telling me if they want a Context, so you need only learn to find out if you need Context for the Activity resources or Application resources. But what if we want to have another page like a separate about page for example? How can we navigate between pages or call external functions?
This is what Intents are for. Intents are sending messages through the application if another function needs to be started, like the launch of a second page.
Within these intents, we have declare the actions that the app needs to do, and if we need a callback, this will also be passed with an Intent. With this code, we are creating an new Intent with Context to our current running Activity to launch the SecondActivity.
Passing data between activities works similar to passing QueryStrings in NavigationsService. Navigate method on WindowsPhone, so you should get familiar with it very fast. The last part that is very important are Views. In a View you declare how the Activity looks like. Think of it as your MainPage. Views can be very different, too. In our getting started project, we also have a Layout file that holds our first View:.
All other controls like Buttons, TextViews etc. This part is totally the same as with the one matching part in the Android SDK, so you will need to get familiar with the Android documentation as well.