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Theming, localization and accessibility

Themes​

PdfViewer ships with two themes, each with light and dark palettes. One of them must be included in App.axaml.

Both themes use the same control template, which only references Pdf* resources. This means the viewer can render if you are using SimpleTheme or a custom application theme, so long as one of the two theme files is included.

<Application.Styles>
    <FluentTheme />
    <StyleInclude Source="avares://Avalonia.Controls.PdfViewer/Themes/Fluent.axaml" />
</Application.Styles>
ThemeDescription
Default.axamlNeutral, rounded, borderless look. Uses its own palette. Does not depend on the host's Avalonia theme.
Fluent.axamlMaps the same keys onto FluentTheme resources. The PDF viewer therefore follows the host's accent and theme variant.

Overriding theme palettes​

Override individual Pdf* resources in App.axaml to replace theme colors with your own. A single override can supply light and dark values through a ResourceDictionary.ThemeDictionaries block.

<Application.Resources>
    <SolidColorBrush x:Key="PdfBackground" Color="#252526" />
    <SolidColorBrush x:Key="PdfErrorForeground" Color="#F48771" />
    <SolidColorBrush x:Key="PdfToolbarBackground" Color="#2D2D30" />
    <SolidColorBrush x:Key="PdfToolbarIconColor" Color="#CCCCCC" />
    <SolidColorBrush x:Key="PdfToolbarTextColor" Color="#E0E0E0" />
    <SolidColorBrush x:Key="PdfToolbarHoverBackground" Color="#3E3E42" />
    <SolidColorBrush x:Key="PdfToolbarBorderColor" Color="#555555" />
    <SolidColorBrush x:Key="PdfToolbarSeparatorColor" Color="#444444" />
    <SolidColorBrush x:Key="PdfMenuIconColor" Color="#AAAAAA" />

    <!-- Chrome the viewer builds in code -->
    <SolidColorBrush x:Key="PdfThumbnailBackground" Color="#2E2E2E" />
    <SolidColorBrush x:Key="PdfThumbnailSelectedBorder" Color="#4A9EDF" />
    <SolidColorBrush x:Key="PdfThumbnailLabelColor" Color="#B0B0B0" />
    <SolidColorBrush x:Key="PdfPagePlaceholderBackground" Color="#2A2A2A" />
    <SolidColorBrush x:Key="PdfDestructiveColor" Color="#FF6B6B" />

    <!-- Highlights and adorners drawn on the page -->
    <SolidColorBrush x:Key="PdfTextSelectionHighlight" Color="#5033A0FF" />
    <SolidColorBrush x:Key="PdfSearchHighlight" Color="#66FFEB3B" />
    <SolidColorBrush x:Key="PdfSearchHighlightActive" Color="#99FF9800" />
    <SolidColorBrush x:Key="PdfAdornerAccent" Color="#33A0FF" />
    <SolidColorBrush x:Key="PdfAdornerHandleBackground" Color="White" />
    <SolidColorBrush x:Key="PdfLinkHoverColor" Color="#DCA0A0A0" />
</Application.Resources>

Pseudoclasses​

PDF viewer exposes these states as pseudoclasses for use by style selectors.

<Style Selector="pdf|PdfViewer:read-only">
    <Setter Property="Opacity" Value="0.9" />
</Style>
PseudoclassState
:has-documentA document is open.
:loadingA document is loading.
:errorAn ErrorMessage is set.
:read-onlyIsReadOnly is true.
:annotatingA tool is active.
:sidebar-openSidebar is expanded.
:mobileCompact mobile layout is in use.
:narrowThe control is narrower than 640 device-independent pixels, such as a phone in portrait. The search field collapses to an icon.
:search-openSearch field is open.
:text-selectedText is selected.
:shape-selectedAn annotation is selected.
:form-field-focusedA form field has focus.
:editing-textInline text editor is open.

Custom templates​

The template parts of PdfViewer are declared with [TemplatePart]. Only PART_ScrollViewer and PART_PagesContainer are required. Every other part is optional. If omitted, the part together with the feature it carries are absent from the customized control.

To build your own theme, copy Default.axaml from the Avalonia.Controls.PdfViewer package. Change the values as desired and include the template in your application styles as described above.

For more information on customizing control templates, see Templated controls and Control themes.

Localization​

All text displayed in PdfViewer comes from PdfViewerStrings, including tooltips, menu entries, dialog text, sidebar labels, placeholders and error messages. This allows you to supply localizations by assigning translated text to Strings.

Strings must be set before loading a document. The toolbar updates immediately on a change, but contextual menus, the Stamp dropdown and thumbnail labels only pick up new strings during a rebuild.

Viewer.Strings = new PdfViewerStrings
{
    Highlight = "Surligner",
    SearchPlaceholder = "Rechercher...",
    PageCountFormat = "sur {0}",
    Loading = "Chargement...",
};

Any untranslated strings keep the default English.

Properties ending in Format are string.Format patterns and must keep their {0} placeholder, for example PageCountFormat ("of {0}") and PageLabelFormat ("Page {0}").

Accessibility​

  • Toolbar and sidebar buttons expose their tooltip as AutomationProperties.Name, so a screen reader announces their tooltip names rather than the control type, e.g., "Highlight" or "Zoom".
  • The control reports as a document region, named from the document title (or file name) and the current page. Set AutomationProperties.Name on the PdfViewer to override.
  • Hidden overlays (e.g., password, go-to-page, custom zoom) are out of the tab order.
  • Form fields are reachable with Tab and show a focus ring. See Forms.
caution

Page content is rendered as a bitmap, so the PDF's text is not automatically exposed to assistive technology. If needed, read the text with GetPageTextAsync and present it in your own accessible surface.

See also​

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