Markup extensions often represent some kind of "shortcut" that enables a XAML file to access a value or behavior that isn't simply declaring elements based on backing types. Some markup extensions can set properties with plain strings or with additionally nested elements, with the goal of streamlining the syntax or the factoring between different XAML files. This usage directs the XAML processing to escape from the general treatment of treating attribute values as either a literal string or a directly string-convertible value.

Instead, a XAML parser calls code that provides behavior for that particular markup extension, and that code provides an alternate object or behavior result that the XAML parser needs. Markup extensions can have arguments, which follow the markup extension name and are also contained within the curly braces.

Typically, an evaluated markup extension provides an object return value. During parsing, that return value is inserted into the position in the object tree where the markup extension usage was in the source XAML. For example you might use this in a control template for a CheckBox , which interprets null as an indeterminate check state triggering the "Indeterminate" visual state. A markup extension generally return an existing instance from some other part of the object graph for the app, or defers a value to run time.

Because you can use a markup extension as an attribute value, and that's the typical usage, you often see markup extensions providing values for reference-type properties that might have otherwise required a property element syntax. For example, here's the syntax for referencing a reusable Style from a ResourceDictionary: Ein Style -Element ist ein Verweistyp, kein einfacher Wert.

By using markup extensions, every property that is settable in XAML is potentially settable in attribute syntax. You can use attribute syntax to provide reference values for a property even if it doesn't otherwise support an attribute syntax for direct object instantiation. Or you can enable specific behavior that defers the general requirement that XAML properties be filled by value types or by newly created reference types.

The Style property takes an instance of the Style class, a reference type that by default could not be created using an attribute syntax string. But in this case, the attribute references a particular markup extension, StaticResource. When that markup extension is processed, it returns a reference to a Style element that was defined earlier as a keyed resource in a resource dictionary. You can nest markup extensions. Die innerste Markuperweiterung wird zuerst ausgewertet. The innermost markup extension is evaluated first.

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For more info see XAML syntax guide. XAML is a declarative language for objects and their properties, but it also includes a syntax for attaching event handlers to objects in the markup. Sie geben den Namen des Ereignisses als Attributnamen in dem Objekt an, in dem das Ereignis behandelt wird.

You specify the name of the event as an attribute name on the object where the event is handled. For the attribute value, you specify the name of an event-handler function that you define in code. The XAML processor uses this name to create a delegate representation in the loaded object tree, and adds the specified handler to an internal handler list.

Nearly all Windows Runtime apps are defined by both markup and code-behind sources. Dies ist ein einfaches Beispiel. Here's a simple example. The Button class supports an event named Click. You can write a handler for Click that runs code that should be invoked after the user clicks the Button.

For the attribute value, provide a string that is the method name of your handler.

When you compile, the compiler now expects that there will be a method named showUpdatesButton-Click defined in the code-behind file, in the namespace declared in the XAML page's x: Also, that method must satisfy the delegate contract for the Click event. Within a project, the XAML is written as a. Class attribute of the root element of the XAML page.

For more info on how these mechanisms work in XAML and how they relate to the programming and application models, see Events and routed events overview. The implementation references the header, and it's technically the header that represents the entry point for the code-behind connection. Resource dictionaries and how to use them is a larger conceptual area that is outside the scope of this topic. In particular it treats the concept of schema quite differently because of its relationship to the backing type concept, and adds language elements such as attached members and markup extensions.

Weitere Informationen finden Sie unter FrameworkElement. For more info, see FrameworkElement. The encoding attribute is valid in XAML. UTF encoding is not supported. The names of XAML elements and attributes are case-sensitive. The value of an attribute is potentially case-sensitive; this depends on how the attribute value is handled for particular properties.

Übersicht über XAML - UWP app developer | Microsoft Docs

For example, if the attribute value declares a member name of an enumeration, the built-in behavior that type-converts a member name string to return the enumeration member value is not case-sensitive. In contrast, the value of the Name property, and utility methods for working with objects based on the name that the Name property declares, treat the name string as case-sensitive. Name or Name applied to XAML elements, particularly the scopes in which names should be relied upon to be unique identifiers. XAML plays several important roles in the app development process. Depending on your own role in the development process, you might not interact with XAML much.

The degree to which you do interact with XAML files also depends on which development environment you are using, whether you use interactive design environment features such as toolboxes and property editors, and the scope and purpose of your Windows Runtime app. Nevertheless, it is likely that during development of the app, you will be editing a XAML file at the element level using a text or XML editor. Using this info, you can confidently edit XAML in a text or XML representation and maintain the validity of that XAML file's declarations and purpose when it is consumed by tools, markup compile operations, or the run-time phase of your Windows Runtime app.

Weitere Tipps zur Leistung, z. For example, there is no way to set a breakpoint within a XAML file. However, there are other techniques that can help you debug issues with UI definitions or other XAML markup while you're still developing your app. In some cases, such as when the XAML represents the first "page" of your application that is loaded as the root visual, the XAML parse exception is not recoverable.

Visual Studio can often provide design-time validation and error checking of a XAML source as you edit it. For example it might display "squiggles" in the XAML text editor as soon as you type a bad attribute value, and you won't even have to wait for a XAML compile pass to see that something's wrong with your UI definition. Fore more info on debugging a Windows Runtime app, see Start a debug session. Windows Sysinternals Administrator's Reference.

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