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Andy (Steve) De GeorgeandGenevieve Warren
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* Add overview article for new WPF (#178) * Remove previous WPF .NET 5 content * Overview article * New article: Create new WPF project (#183) * Basic index file * Finish article for new project. * acro * markdown fix * Fix build errors * fix code lang * fix code lang * Add differences article for WPF (#186) * Fix VS version for create app * Add differences article * Minor * fix overview styles code * Add code langs for overview * Port Window Overview WPF article (#1011) * Add Window overview article * Add TOC * Remove temp code * Fix headers * Port final Windows related articles (#1015) * Initial test commit * Add system dialogs * 75% complete * Add images * Fix linter * Add to toc * Add more howto * Fix code * Add get/set main window * Add missing code * Add to toc * Fix warnings * Fix warnings * missing code * Update see also * fix xref * Migrate wpf net core controls-styles articles (#1023) * Migrate control-styles * Fix links * Fix links * Port databinding article. (#1022) * Migrated databinding overview * update toc * Fix links/snippets * fix links * Move to correct folder * Port initial resources docs (#1026) * initial resources docs * Build errors * Update dotnet-desktop-guide/net/wpf/systems/xaml-resources-overview.md Co-authored-by: Genevieve Warren <[email protected]> * Apply suggestions from code review Co-authored-by: Genevieve Warren <[email protected]> * Feedback * Add app article * Add system article * Minor * meta * fix toc * Apply suggestions from code review Co-authored-by: Genevieve Warren <[email protected]> Co-authored-by: Genevieve Warren <[email protected]> * Add xaml article * reformat redirect * Redirects * WPF update XAML article (#1031) * convert snippets * minor edits * minor * Fix warnings * Fixes #1028 * Fixes #1028 * Apply suggestions from code review Co-authored-by: Genevieve Warren <[email protected]> * update redirects Co-authored-by: Genevieve Warren <[email protected]> * minor updates to link * Readd migration article * Warning fixes * Fix lint * Minor updates * Fix warnings for TOC/YML * last warnings Co-authored-by: Genevieve Warren <[email protected]>
50 lines
2.4 KiB
Markdown
50 lines
2.4 KiB
Markdown
---
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title: "x:Null Markup Extension"
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description: "Describes how the x:Null markup extension is handled by XAML."
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ms.date: "03/30/2017"
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f1_keywords:
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- "NullExtension"
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- "x:NullExtension"
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- "x:Null"
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- "Null"
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- "xNull"
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helpviewer_keywords:
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- "Null markup extension in XAML [XAML Services]"
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- "x:Null markup extension [XAML Services]"
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- "XAML [XAML Services], x:Null markup extension"
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ms.assetid: 2e3ccc21-4996-481d-91b5-3910d8b3bfa3
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---
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# x:Null Markup Extension
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Specifies `null` as a value for a XAML member.
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## XAML Attribute Usage
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```xaml
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<object property="{x:Null}" .../>
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```
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## Remarks
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The keyword for a null reference in C# and C++ is null. The Microsoft Visual Basic keyword for a null reference is `Nothing`, but you always use `{x:Null}` as the XAML usage regardless which code-behind language you associate with the XAML.
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The `x:Null` markup extension has no settable properties.
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A null usage is often associated with the XAML member exposure of a CLR <xref:System.Nullable%601> value.
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The `x:Null` markup extension, like all XAML markup extensions, uses the braces (`{,}`) for escaping the handling of attribute values to be other than literals or event-handler references. Attribute syntax is the syntax most frequently used with this markup extension. An object element syntax `<x:Null />` is technically possible, but is rarely used because the `x:Null` markup extension has no positional parameters or construction arguments.
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For information about markup extensions, see [Markup Extensions and WPF XAML](../framework/wpf/advanced/markup-extensions-and-wpf-xaml.md).
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In .NET XAML Services, the handling for this markup extension is defined by the <xref:System.Windows.Markup.NullExtension> class.
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## WPF Usage Notes
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Note that `null` is not necessarily the initial unset value for a reference-type dependency property. The initial default value can vary for each dependency property and can be based on property-specific metadata. Many dependency properties do not accept `null` as a value, either through markup or code because of their validation callback implementations. For more information about dependency properties, see [Dependency Properties Overview](../framework/wpf/advanced/dependency-properties-overview.md).
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## See also
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- <xref:System.Windows.DependencyProperty.UnsetValue>
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- [XAML overview (WPF .NET)](../net/wpf/xaml/index.md)
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- [Markup Extensions and WPF XAML](../framework/wpf/advanced/markup-extensions-and-wpf-xaml.md)
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