AbsoluteLayout和XAML
如您所见，您可以使用Children集合中可用的Add方法之一或通过静态方法调用设置附加属性，在代码中定位和确定AbsoluteLayout的子项的大小。
但是，你如何在XAML中设置AbsoluteLayout子项的位置和大小？
涉及一种非常特殊的语法。 这个语法由早期Abso？luteDemo程序的XAML版本说明，名为AbsoluteXamlDemo：
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="AbsoluteXamlDemo.AbsoluteXamlDemoPage">
<AbsoluteLayout Padding="50">
<BoxView Color="Accent"
AbsoluteLayout.LayoutBounds="0, 10, 200, 5" />
<BoxView Color="Accent"
AbsoluteLayout.LayoutBounds="0, 20, 200, 5" />
<BoxView Color="Accent"
AbsoluteLayout.LayoutBounds="10, 0, 5, 65" />
<BoxView Color="Accent"
AbsoluteLayout.LayoutBounds="20, 0, 5, 65" />
<Label Text="Stylish Header"
FontSize="24"
AbsoluteLayout.LayoutBounds="30, 25, AutoSize, AutoSize" />
<Label AbsoluteLayout.LayoutBounds="0, 80, AutoSize, AutoSize">
<Label.FormattedText>
<FormattedString>
<Span Text="Although " />
<Span Text="AbsoluteLayout"
FontAttributes="Italic" />
<Span Text=
" is usually employed for purposes other
than the display of text using " />
<Span Text="Label"
FontAttributes="Italic" />
<Span Text=
", obviously it can be used in that way.
The text continues to wrap nicely
within the bounds of the container
and any padding that might be applied." />
</FormattedString>
</Label.FormattedText>
</Label>
</AbsoluteLayout>
</ContentPage>代码隐藏文件仅包含InitializeComponent调用。
这是第一个BoxView：
<BoxView Color="Accent"
AbsoluteLayout.LayoutBounds="0, 10, 200, 5" />在XAML中，附加的可绑定属性表示为由类名（Ab？soluteLayout）和以句点分隔的属性名（LayoutBounds）组成的属性。 每当您看到这样的属性时，它始终是一个附加的可绑定属性。 这是该属性语法的唯一应用。
总之，类名和属性名的组合仅在三个特定上下文中出现在XAML中：如果它们显示为元素，则它们是属性元素。 如果它们显示为属性，则它们是附加的可绑定属性。 并且类名和属性名的唯一其他上下文是对x：Static标记扩展的定义。
AbsoluteLayout.LayoutBounds属性通常设置为由逗号分隔的四个数字。 您还可以将AbsoluteLayout.LayoutBounds表示为属性元素：
<BoxView Color="Accent">
<AbsoluteLayout.LayoutBounds>
0, 10, 200, 5
</AbsoluteLayout.LayoutBounds>
</BoxView>这四个数字由BoundsTypeConverter而不是RectangleTypeConverter解析，因为BoundsTypeConverter允许对宽度和高度部分使用AutoSize。 您可以在AbsoluteXamlDemo XAML文件中看到AutoSize参数：
<Label Text="Stylish Header"
FontSize="24"
AbsoluteLayout.LayoutBounds="30, 25, AutoSize, AutoSize" />
Or you can leave them out:
<Label Text="Stylish Header"
FontSize="24"
AbsoluteLayout.LayoutBounds="30, 25" />您在XAML中指定的附加可绑定属性的奇怪之处在于它们并不存在！ AbsoluteLayout中没有名为LayoutBounds的字段，属性或方法。有一个名为LayoutBoundsProperty的BindableProperty类型的公共静态只读字段，并且有名为SetLayoutBounds和GetLayoutBounds的公共静态方法，但没有任何名为LayoutBounds的方法。 XAML解析器将语法识别为引用附加的可绑定属性，然后在AbsoluteLayout类中查找LayoutBoundsProperty。从那里，它可以使用该BindableProperty对象和BoundsTypeConverter中的值在目标视图上调用SetValue。
Chessboard系列程序似乎不太可能在XAML中复制，因为该文件需要32个BoxView实例而没有循环的好处。但是，ChessboardXaml程序显示了如何以隐式样式指定BoxView的两个属性，包括AbsoluteLayout.LayoutFlags附加的可绑定属性：
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="ChessboardXaml.ChessboardXamlPage">
<ContentPage.Padding>
<OnPlatform x:TypeArguments="Thickness"
iOS="5, 25, 5, 5"
Android="5"
WinPhone="5" />
</ContentPage.Padding>
<ContentPage.Resources>
<ResourceDictionary>
<Style TargetType="BoxView">
<Setter Property="Color" Value="#004000" />
<Setter Property="AbsoluteLayout.LayoutFlags" Value="All" />
</Style>
</ResourceDictionary>
</ContentPage.Resources>
<ContentView SizeChanged="OnContentViewSizeChanged">
<AbsoluteLayout x:Name="absoluteLayout"
BackgroundColor="#F0DC82"
VerticalOptions="Center"
HorizontalOptions="Center">
<BoxView AbsoluteLayout.LayoutBounds="0.00, 0.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.29, 0.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.57, 0.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.86, 0.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.14, 0.14, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.43, 0.14, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.71, 0.14, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="1.00, 0.14, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.00, 0.29, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.29, 0.29, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.57, 0.29, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.86, 0.29, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.14, 0.43, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.43, 0.43, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.71, 0.43, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="1.00, 0.43, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.00, 0.57, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.29, 0.57, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.57, 0.57, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.86, 0.57, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.14, 0.71, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.43, 0.71, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.71, 0.71, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="1.00, 0.71, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.00, 0.86, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.29, 0.86, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.57, 0.86, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.86, 0.86, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.14, 1.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.43, 1.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="0.71, 1.00, 0.125, 0.125" />
<BoxView AbsoluteLayout.LayoutBounds="1.00, 1.00, 0.125, 0.125" />
</AbsoluteLayout>
</ContentView>
</ContentPage>是的，它是很多单独的BoxView元素，但你不能争论文件的清洁度。 代码隐藏文件只是调整宽高比：
public partial class ChessboardXamlPage : ContentPage
{
public ChessboardXamlPage()
{
InitializeComponent();
}
void OnContentViewSizeChanged(object sender, EventArgs args)
{
ContentView contentView = (ContentView)sender;
double boardSize = Math.Min(contentView.Width, contentView.Height);
absoluteLayout.WidthRequest = boardSize;
absoluteLayout.HeightRequest = boardSize;
}
} 
