x:DataType<\/code> attribute on any VisualElement<\/code> you can enable a compiled binding. <\/p>\nBenefits<\/h2>\n
Using these bindings offer a few major benefits for you and your app:<\/p>\n
\n- Compile-time validation for all binding expressions.<\/li>\n
- Performance improvements as bindings are resolved at compile time.<\/li>\n<\/ol>\n
Enabling XAML Compilation<\/h2>\n
A pre-requisite to use these bindings is that your app must turn on XAML Compilation<\/a>. This is the default in all new apps and greatly improves performance in apps when using XAML. You can enable it by adding an assembly flag in your shared code:<\/p>\n\r\n[assembly:XamlCompilation(XamlCompilationOptions.Compile)]\r\n<\/code><\/pre>\nUsing Compiled Bindings<\/h2>\n
Let's use an example of a page that displays a list of Monkeys in a ListView<\/code>. This means we have a Monkey<\/code> with properties on it about the monkey, a MonkeysViewModel<\/code> that has data objects to bind to for the list, and a MonkeysPage<\/code> that is our user interface in XAML.<\/p>\nHere is what the user interface looks like to display a list of monkeys and the current count:<\/p>\n
\r\n<ContentPage \r\n xmlns=\"http:\/\/xamarin.com\/schemas\/2014\/forms\" \r\n xmlns:x=\"http:\/\/schemas.microsoft.com\/winfx\/2009\/xaml\" \r\n x:Class=\"Monkeys.Views.MonkeysPage\"\r\n Title=\"Monkeys\">\r\n<StackLayout>\r\n <Label Margin=\"10,0\" Text=\"{Binding MonkeyCount, StringFormat='{0} Monkeys'}\"\/>\r\n <ListView ItemsSource=\"{Binding Monkeys}\"\r\n HasUnevenRows=\"true\">\r\n <ListView.ItemTemplate>\r\n <DataTemplate>\r\n <ViewCell>\r\n <Grid Padding=\"10\" RowSpacing=\"10\" ColumnSpacing=\"10\">\r\n <Grid.ColumnDefinitions>\r\n <ColumnDefinition Width=\"Auto\"\/>\r\n <ColumnDefinition Width=\"*\"\/>\r\n <\/Grid.ColumnDefinitions>\r\n <controls:CircleImage \r\n BorderColor=\"Aqua\"\r\n BorderThickness=\"3\"\r\n HeightRequest=\"66\"\r\n WidthRequest=\"66\"\r\n HorizontalOptions=\"CenterAndExpand\"\r\n VerticalOptions=\"CenterAndExpand\"\r\n Aspect=\"AspectFill\"\r\n Source=\"{Binding Image}\"\/>\r\n <StackLayout VerticalOptions=\"Center\">\r\n <Label Text=\"{Binding Name}\"\/>\r\n <Label Text=\"{Binding Location}\"\/>\r\n <\/StackLayout>\r\n <\/Grid>\r\n <\/ViewCell>\r\n <\/DataTemplate>\r\n <\/ListView.ItemTemplate>\r\n <\/ListView>\r\n<\/ContentPage>\r\n<\/code><\/pre>\nNotice that we are binding from the MonkeysViewModel<\/code> to MonkeyCount<\/code> and Monkeys<\/code> and additionally to the Image<\/code>, Name<\/code>, and Location<\/code> of each monkey inside of the ItemTemplate<\/code>. <\/p>\nTo enable these bindings for the MonkeysViewModels<\/code> we will bring in the namespace that it is in:<\/p>\n\r\nxmlns:viewmodels=\"clr-namespace:Monkeys.ViewModels\"\r\n<\/pre>\nThen on the ContentPage<\/code> node we can add the x:DataType<\/code> property:<\/p>\n\r\n<ContentPage \r\n xmlns=\"http:\/\/xamarin.com\/schemas\/2014\/forms\" \r\n xmlns:x=\"http:\/\/schemas.microsoft.com\/winfx\/2009\/xaml\" \r\n x:Class=\"Monkeys.Views.MonkeysPage\"\r\n xmlns:viewmodels=\"clr-namespace:Monkeys.ViewModels\"\r\n x:DataType=\"viewmodels:MonkeysViewModel\"\r\n Title=\"Monkeys\">\r\n<\/ContentPage>\r\n<\/pre>\nThat is all it takes to start! Now, if for some reason we have a spelling mistake in our bindings when we compile the library we will get an error as the bindings will now be validated.<\/p>\n
![\"Compiled](\"http:\/\/devblogs.microsoft.com\/xamarin\/wp-content\/uploads\/sites\/44\/2019\/08\/Compiled.png\")
<\/p>\n
If you are using any control that has a DataTemplate<\/code> you must also setup the compiled binding on it. In this app, we have a ListView that is data bound to anObservableCollection<Monkey><\/code>. We can bring in the Monkey<\/code>'s namespace just like we did for the MonkeysViewModel<\/code>. <\/p>\n\r\nxmlns:models=\"clr-namespace:Monkeys.Models\"\r\n<\/pre>\nThen on the DataTemplate<\/code>, we can specify the x:DataType<\/code> like we did before:<\/p>\n\r\n<ListView ItemsSource=\"{Binding Monkeys}\"\r\n HasUnevenRows=\"true\">\r\n <ListView.ItemTemplate>\r\n <DataTemplate x:DataType=\"models:Monkey\">\r\n <ViewCell>\r\n <\/ViewCell>\r\n <\/DataTemplate>\r\n <\/ListView.ItemTemplate>\r\n<\/ListView>\r\n<\/pre>\nAnd just like that we have enabled this on our entire page and it only took a few seconds.<\/p>\n
Learn More<\/h2>\n
There are a lot more ways to use compiled bindings in your Xamarin.Forms apps, so be sure to read through the comprehensive documentation<\/a>. You can find a sample used in this blog on GitHub<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"See how compiled bindings for Xamarin.Forms XAML can help boost performance in your apps and also give immediate feedback when developing apps if you have a typo in your bindings.<\/p>\n","protected":false},"author":544,"featured_media":45218,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[2,367],"tags":[6821,648,5841],"class_list":["post-45216","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-developers","category-xamarin-forms","tag-compiled-bindings","tag-performance","tag-xaml"],"acf":[],"blog_post_summary":"
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