The Application base class offers the following features, which are exposed in your projects default App subclass:. Depending on which template you chose, the App class could be defined in one of two ways:. The MainPage property on the Application class sets the root page of the application.
For example, you can create logic in your App class to display a different page depending on whether the user is logged in or not. The Application subclass has a static Properties dictionary which can be used to store data, in particular for use in the OnStartOnSleepand OnResume methods.
This can be accessed from anywhere in your Xamarin. Forms code using Application. The Properties dictionary uses a string key and stores an object value.
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For example, you could set a persistent "id" property anywhere in your code when an item is selected, in a page's OnDisappearing method, or in the OnSleep method like this:. In the OnStart or OnResume methods you can then use this value to recreate the user's experience in some way. The Properties dictionary stores object s so you need to cast its value before using it.
The Properties dictionary can only serialize primitive types for storage. The Properties dictionary is saved to the device automatically. Data added to the dictionary will be available when the application returns from the background or even after it is restarted. Forms 1. This is to allow you to save properties after important updates rather than risk them not getting serialized out due to a crash or being killed by the OS.
Forms book chapters 615and 20and in the associated samples. This class is then instantiated in each platform-specific project and passed to the LoadApplication method which is where the MainPage is loaded and displayed to the user. The code for each platform is shown in the following sections.
The latest Xamarin. Forms solution templates already contain all this code, preconfigured for your app. It should:. The C code behind construction must call LoadApplication to create an instance of your Xamarin. Forms App. Note that it is good practice to explicitly use the application namespace to qualify the App because UWP applications also have their own App class unrelated to Xamarin.
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I found that I had to handle android hardware back button in AppShell. It took quite a bit of digging, but I found a public Shell interface that meets this need. Below is a code snippet, YMMV.
Learn more. Ask Question. Asked 7 months ago. Active yesterday. Viewed times. I am developing a Xamarin Forms app using App Shell. Content as MyContentPage.
Best regards. Ivoryguard Ivoryguard 31 2 2 bronze badges. You can use MessaginCenter to call MyMethod docs. Why exactly do you need to know which ContentPage is being displayed? I also see you want to call MyMethod, it would help if I knew what it did! I added a Content Page which has a WebView control. I want to call WebViewControl. GoBack method when android back button is pressed, not close my app.
Have you resolved this question? Active Oldest Votes. Nick W. 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. Featured on Meta. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Question Close Updates: Phase 1. Dark Mode Beta - help us root out low-contrast and un-converted bits. Related 1.Settings allow the separation of data that configures the behavior of an app from the code, allowing the behavior to be changed without rebuilding the app.
There are two types of settings: app settings, and user settings. App settings are data that an app creates and manages.
It can include data such as fixed web service endpoints, API keys, and runtime state. App settings are tied to the existence of the app and are only meaningful to that app. User settings are the customizable settings of an app that affect the behavior of the app and don't require frequent re-adjustment. For example, an app might let the user specify where to retrieve data from, and how to display it on the screen. Forms includes a persistent dictionary that can be used to store settings data.
This dictionary can be accessed using the Application. Properties property, and any data that's placed into it is saved when the app goes into a sleep state, and is restored when the app resumes or starts up again. In addition, the Application class also has a SavePropertiesAsync method that allows an app to have its settings saved when required. For more information about this dictionary, see Properties Dictionary.
A downside to storing data using the Xamarin. Forms persistent dictionary is that it's not easily data bound to. Therefore, the eShopOnContainers mobile app uses the Xam. Settings library, available from NuGet. This library provides a consistent, type-safe, cross-platform approach for persisting and retrieving app and user settings, while using the native settings management provided by each platform.
In addition, it's straightforward to use data binding to access settings data exposed by the library. While the Xam. Settings library can store both app and user settings, it makes no distinction between the two.
When using the Xam. Settings library, a single static class should be created that will contain the app and user settings required by the app. The following code example shows the Settings class in the eShopOnContainers mobile app:. Settings library. Currentand an app's settings class should expose this singleton via an ISettings property. Using directives for the Plugin. Settings and Plugin.
Abstractions namespaces should be added to a class that requires access to the Xam. Settings library types. Each setting consists of a key, a default value, and a property. The following code example shows all three items for a user setting that represents the base URL for the online services that the eShopOnContainers mobile app connects to:.
The key is always a const string that defines the key name, with the default value for the setting being a static readonly value of the required type. Providing a default value ensures that a valid value is available if an unset setting is retrieved.
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The ISettings. GetValueOrDefault method is used to retrieve a setting's value from platform-specific storage. If no value is defined for the setting, its default value is retrieved instead. Similarly, the ISettings. AddOrUpdateValue method is used to persist a setting's value to platform-specific storage.Download the sample.
The NavigationPage class provides a hierarchical navigation experience where the user is able to navigate through pages, forwards and backwards, as desired. This article demonstrates how to use the NavigationPage class to perform navigation in a stack of pages.
To move from one page to another, an application will push a new page onto the navigation stack, where it will become the active page, as shown in the following diagram:. To return back to the previous page, the application will pop the current page from the navigation stack, and the new topmost page becomes the active page, as shown in the following diagram:. Navigation methods are exposed by the Navigation property on any Page derived types. These methods provide the ability to push pages onto the navigation stack, to pop pages from the navigation stack, and to perform stack manipulation.
In hierarchical navigation, the NavigationPage class is used to navigate through a stack of ContentPage objects. The following screenshots show the main components of the NavigationPage on each platform:. The layout of a NavigationPage is dependent on the platform:. On all the platforms, the value of the Page. Title property will be displayed as the page title.
It's recommended that a NavigationPage should be populated with ContentPage instances only. The first page added to a navigation stack is referred to as the root page of the application, and the following code example shows how this is accomplished:.
This causes the Page1Xaml ContentPage instance to be pushed onto the navigation stack, where it becomes the active page and the root page of the application. This is shown in the following screenshots:. The RootPage property of a NavigationPage instance provides access to the first page in the navigation stack.
To navigate to Page2Xamlit is necessary to invoke the PushAsync method on the Navigation property of the current page, as demonstrated in the following code example:.
This causes the Page2Xaml instance to be pushed onto the navigation stack, where it becomes the active page. When the PushAsync method is invoked, the following events occur:. However, the precise order in which these events occur is platform dependent. For more information, see Chapter 24 of Charles Petzold's Xamarin. Forms book.
Calls to the OnDisappearing and OnAppearing overrides cannot be treated as guaranteed indications of page navigation. For example, on iOS, the OnDisappearing override is called on the active page when the application terminates. The active page can be popped from the navigation stack by pressing the Back button on the device, regardless of whether this is a physical button on the device or an on-screen button. To programmatically return to the original page, the Page2Xaml instance must invoke the PopAsync method, as demonstrated in the following code example:.
This causes the Page2Xaml instance to be removed from the navigation stack, with the new topmost page becoming the active page. When the PopAsync method is invoked, the following events occur:. For more information see Chapter 24 of Charles Petzold's Xamarin. This method pops all but the root Page off the navigation stack, therefore making the root page of the application the active page.
The Navigation property of each page also provides overridden push and pop methods that include a boolean parameter that controls whether to display a page animation during navigation, as shown in the following code example:.Hi, I want to get the currnetpage instance inorder to handle the back button functionality in android using xamarin forms. You cannot get the current page. There is no API for this. May I ask what you are trying to accomplish regarding the back button?
My requirement is the app should move like 4 to 3, 3 to 2 and from 2 the app should close when pressing android back button. Is there any way to accomplish this. If screen one is kind of a login screen, start your app with screen 2 and then show screen 1 modally.
That will give you the expected behavior. You're not supposed to exit an app manually. I have a MasterDetail Page and also a login is required. I cannot load the MasterDetail Page first and then show the login modally, because the masterdetail page loads the detail page, and in the detail page I need to be logged in to retrieve data. I can do a conditional data loading depending if the user is logged in or not, but I could not find a way to reload the detail page after the user logged in when doing Navigation.
PopAsync from LoginPage. Alternatively try this different login pattern. While it is true that there is no direct access to the Current Page in the API, it is possible to work out which Page it is via the navigation stacks.
Obviously its slightly more fiddly than that because you have to factor in the other stack, the ModalStack. But if you bear LIFO in mind, it wont be difficult Apologies for bumping such an old thread, but I felt it would be pointless to have two threads on the same question.
July in Xamarin. Thanks, sunil. July August December That alternative login pattern is great - so much easier than showing and hiding modals.In the previous guide, we developed a Xamarin app that displays on a list of items fetched from the internet.
In this guide, we go further by opening a detail view when we tap on an item.
We will first create the new view without complying to the mvvm pattern. After that, we will try to modify the code in order to follow mvvm principles. Adding the detail page without considering mvvm is the easier and straightforward way. The view model defines a property of type Post which is bound to the xaml view. The constructor of the page takes a parameter of type of type Post and passes it to the view model.
Here is the code for each file:. In order to display this new view when the user taps the on an item on the list, we need to handle the corresponding event on the ListView control. Here is the implementation of that function:. What we did here is that we ask the Navigation property inherited from the ContentPage class to navigate to a new page. This new page is an instance of PostDetail class that takes the selected post as a parameter. Launch the app and tap on an item in the list.
The detail page of that item should appear. Here, we did it …, or not. In fact, the code does not really follow mvvm principles. Here are some of the sins of this code:. We start by supporting the selected item command.
A command is a mechanism that allows to handle events in the view model. It works by binding a kind-of event in the control to a command in the view model. In order for this to work we need these elements to be satisfied.
The second and third conditions are very easy to satisfy, because it is easy to define a command and to bind it. However, there is one little gotcha. The ListView control does not accept natively a command property for the item selected event. Since we are not going to buy a richer ListView controlwe need to find another cue. Hopefully, there is a quite powerful technique in Xamarin that allows to exactly do that.
It is called behaviors.We have covered the theory behind saving state in the Activity Lifecycle guide; now, let's walk through an example. This is a very simple project that has two activities to demonstrate the activity lifecycle and how the various lifecycle methods are called.
When you start the application, the screen of MainActivity is displayed:. Each method in this sample writes to the IDE application output window to indicate activity state. Next, we're going to change the application so that we have a button that counts and displays the number of times it is clicked.
The resulting Main. Let's add the following code to the end of the OnCreate method in MainActivity — this code handles click events from the clickButton :. Examining the application output, we see that Activity A was paused, stopped, destroyed, recreated, restarted, then resumed during the rotation from portrait to landscape mode:. Because Activity A is destroyed and recreated again when the device is rotated, its instance state is lost.
Next, we will add code to save and restore the instance state. Let's add a method to MainActivity to save the instance state. Let's use it to save our click count as an integer value:.
Add the following code just before the line where clickbutton is defined:. Build and run the app again, then click the second button a few times. When we rotate the device to landscape mode, the count is preserved!Xamarin Forms Tutorials 5 : CarouselPage
You may also leave feedback directly on GitHub. Skip to main content. Exit focus mode. When you start the application, the screen of MainActivity is displayed: Viewing State Transitions Each method in this sample writes to the IDE application output window to indicate activity state.
When the app first starts, the output window displays the state changes of Activity A : [ActivityLifecycle. SecondActivity] Activity B - OnDestroy Adding a Click Counter Next, we're going to change the application so that we have a button that counts and displays the number of times it is clicked.
GetString Resource. Debug GetType. Add the following code just before the line where clickbutton is defined: if bundle! Let's take a look at the output window to see what happened: [ActivityLifecycle. Summary In this walkthough, we have used our knowledge of the Activity Lifecycle to preserve state data. Yes No. Any additional feedback? Skip Submit. Send feedback about This product This page. This page. Submit feedback. There are no open issues. View on GitHub. Is this page helpful?