WPF中,CSS em单位的类比是什么?
[MarkupExtensionReturnType(typeof(double))]
public class EmFontSize : MarkupExtension
{
public EmFontSize() { }
public EmFontSize(double size)
{
Size = size;
}
[ConstructorArgument("size")]
public double Size { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
if (serviceProvider == null)
return null;
// get the target of the extension from the IServiceProvider interface
IProvideValueTarget ipvt = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
if (ipvt.TargetObject.GetType().FullName == "System.Windows.SharedDp")
return this;
DependencyObject targetObject = ipvt.TargetObject as DependencyObject;
var window = TryFindParent<Window>(targetObject);
if (window != null)
{
return window.FontSize * Size;
}
return 12 * Size;
}
public static T TryFindParent<T>(DependencyObject child) where T : DependencyObject
{
//get parent item
DependencyObject parentObject = GetParentObject(child);
//we've reached the end of the tree
if (parentObject == null) return null;
//check if the parent matches the type we're looking for
T parent = parentObject as T;
if (parent != null)
{
return parent;
}
else
{
//use recursion to proceed with next level
return TryFindParent<T>(parentObject);
}
}
public static DependencyObject GetParentObject(DependencyObject child)
{
if (child == null) return null;
//handle content elements separately
ContentElement contentElement = child as ContentElement;
if (contentElement != null)
{
DependencyObject parent = ContentOperations.GetParent(contentElement);
if (parent != null) return parent;
FrameworkContentElement fce = contentElement as FrameworkContentElement;
return fce != null ? fce.Parent : null;
}
//also try searching for parent in framework elements (such as DockPanel, etc)
FrameworkElement frameworkElement = child as FrameworkElement;
if (frameworkElement != null)
{
DependencyObject parent = frameworkElement.Parent;
if (parent != null) return parent;
}
//if it's not a ContentElement/FrameworkElement, rely on VisualTreeHelper
return VisualTreeHelper.GetParent(child);
}
}
使用示例
xmlns:my="clr-namespace:FontSizeExample"
<TextBlock Text="Sample Font" FontSize="{my:EmFontSize 1.1}"/>
<TextBlock Text="Sample Font" FontSize="{my:EmFontSize .9}"/>
em大小是当前字体中大写字母M的宽度,在Wpf中没有依赖于字体的大小调整方法。
顺便说一下,WPF使用“设备独立像素”,它们始终是1/96英寸(因为这是今天显示器上的一个像素),所以:
在显示器上这些数值非常不准确,因为几乎所有的显示器都报告96DPI分辨率并忽略真实的像素大小,但在打印时非常有用。
<ScaleTransform ScaleX="1.2" ScaleY="1.2"></ScaleTransform>
很遗憾,在WPF中没有em单位的等效物。所有字体大小等都始终以像素为单位设置。