我目前正在尝试使用带有我的条目FontSize属性扩展名的静态资源。我有这段代码：
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
x:Class="PROJECT.Sources.Pages.Extras.EditProfilePage"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:control="clr-namespace:PROJECT.Sources.Controls;assembly=PROJECT"
xmlns:extension="clr-namespace:PROJECT.Sources.Extensions;assembly=PROJECT"
xmlns:sys="clr-namespace:System;assembly=mscorlib">
<ContentPage.Resources>
<ResourceDictionary>
<Color x:Key="NL_BlueNight">#0E1728</Color>
<Color x:Key="NL_OrangeBeer">#E87E07</Color>
<Color x:Key="NL_OrangeSky">#BD4327</Color>
<Color x:Key="NL_White">#ECECEC</Color>
<sys:Double x:Key="EntryFontSize">20</sys:Double>
</ResourceDictionary>
</ContentPage.Resources>
<ContentPage.Content>
<AbsoluteLayout BackgroundColor="{x:StaticResource NL_BlueNight}">
<AbsoluteLayout
Margin="{Binding LayoutThicknessAdapter}"
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Black">
<control:Gif
AbsoluteLayout.LayoutBounds="0.5, 0, 1, 0.9"
AbsoluteLayout.LayoutFlags="All"
GifSource="Gifs/LoginBackground.gif" />
<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent" />
</AbsoluteLayout>
<AbsoluteLayout
Margin="{Binding LayoutThicknessAdapter}"
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="{StaticResource NL_BlueNight}"
Opacity="0.8">
<ScrollView AbsoluteLayout.LayoutBounds="0.5, 0, 1, 0.9" AbsoluteLayout.LayoutFlags="All">
<StackLayout
HorizontalOptions="Fill"
Orientation="Vertical"
Spacing="15"
VerticalOptions="CenterAndExpand">
<BoxView BackgroundColor="Transparent" HeightRequest="{Binding SeparatorHeight}" />
<control:CustomImageCircle
x:Name="UserProfileImageButton"
HeightRequest="{Binding PictureHeightWidth}"
HorizontalOptions="Center"
Source="{Binding CurrentUser.ImageProfile}"
VerticalOptions="Center"
WidthRequest="{Binding PictureHeightWidth}" />
<Image
HeightRequest="{Binding SeparatorHeight}"
HorizontalOptions="Center"
Source="{extension:ImageSource LogoPROJECT.png}" />
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
Placeholder="pseudo"
PlaceholderColor="Gray"
Text="{Binding CurrentUser.Pseudo}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
Placeholder="email"
PlaceholderColor="Gray"
Text="{Binding CurrentUser.Email}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
Placeholder="firstname"
PlaceholderColor="Gray"
Text="{Binding CurrentUser.Firstname}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
Placeholder="lastname"
PlaceholderColor="Gray"
Text="{Binding CurrentUser.Lastname}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
Keyboard="Telephone"
Placeholder="phone number"
PlaceholderColor="Gray"
Text="{Binding CurrentUser.Number}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
IsPassword="True"
Placeholder="password"
PlaceholderColor="Gray"
Text="{Binding PasswordOne}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="{Binding EntryHeight}" WidthRequest="{Binding EntryWidth}">
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="{extention:FontSize StaticResourceKey=EntryFontSize}}"
HasBorder="false"
IsPassword="True"
Placeholder="password (retype)"
PlaceholderColor="Gray"
Text="{Binding PasswordTwo}"
TextColor="White"
XAlign="Center" />
<!--<BoxView
AbsoluteLayout.LayoutBounds="0.5, 0.7, 0.8, 1"
AbsoluteLayout.LayoutFlags="XProportional, YProportional, WidthProportional"
BackgroundColor="{StaticResource NL_OrangeBeer}" />-->
</AbsoluteLayout>
</StackLayout>
</ScrollView>
<AbsoluteLayout
AbsoluteLayout.LayoutBounds="0.5,1,1,0.1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="{StaticResource NL_OrangeBeer}">
<control:CustomLabel
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
FontFamily="{extension:FontFamily Roboto_Light}"
FontSize="35"
HorizontalTextAlignment="Center"
Text="Save and Return"
TextColor="White"
VerticalTextAlignment="Center" />
<control:CustomButton
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
BorderColor="Transparent"
Clicked="OnSaveClicked" />
</AbsoluteLayout>
<AbsoluteLayout
AbsoluteLayout.LayoutBounds="0, 0, 0.1, 0.1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
IsVisible="{Binding IsReturnVisible}">
<control:CustomImage
AbsoluteLayout.LayoutBounds="0.5, 0.5, 0.8, 0.8"
AbsoluteLayout.LayoutFlags="All"
Aspect="AspectFit"
Source="{extension:ImageSource cross.png}" />
<control:CustomButton
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.LayoutFlags="All"
BackgroundColor="Transparent"
BorderColor="Transparent"
Clicked="OnReturnClicked" />
</AbsoluteLayout>
</AbsoluteLayout>
</AbsoluteLayout>
</ContentPage.Content>
</ContentPage>
来自extension:FontSize的地方：
[ContentProperty("FontSize")]
public class FontSizeExtension : IMarkupExtension
{
public double FontSize { get; set; }
public object ProvideValue(IServiceProvider serviceProvider)
{
return Services.Sizing.FontSizeAdapter(FontSize);
}
}
Sizing.cs
public class Sizing
{
public static double FontSizeAdapter(double fontSize)
{
switch (Device.RuntimePlatform)
{
case "Android":
return (fontSize / 2);
case "iOS":
return fontSize;
case "Windows":
case "WinPhone":
return fontSize;
default:
return fontSize;
}
}
}
然而，当我执行FontSize="{extention:FontSize {x:StaticResource EntryFontSize}}"时，它会抛出一个异常，表示该值不能为null。如何同时使用这两个值？我指的是 x：StaticResource 和扩展程序
谢谢！
答案 0 :(得分：2)
<强> 1。确保正确定义和使用前缀
确保检查为前缀提供的命名空间对于标记扩展是否正确，并且在指定前缀时没有拼写错误。这应该解决'值不能为空'错误。
<强> 2。使用嵌套标记扩展
时指定属性名称使用嵌套标记扩展时，需要指定扩展的属性名称。否则，我的测试显示，它被视为字符串值并分配给默认内容属性。这应解决错误'输入字符串格式不正确'。
解决方案-1：指定属性名称
<control:CustomEntry
AbsoluteLayout.LayoutBounds="0.5, 0.5, 1, 1"
AbsoluteLayout.Flags="All"
...
FontSize="{extension:FontSize FontSize={x:StaticResource EntryFontSize}}"
.../>
解决方案-2 ：您可以通过在标记扩展中添加StaticResourceKey属性来进一步简化此操作：
[ContentProperty("FontSize")]
public class FontSizeExtension : IMarkupExtension
{
public double FontSize { get; set; }
public string StaticResourceKey { get; set; }
public object ProvideValue(IServiceProvider serviceProvider)
{
if (serviceProvider == null)
throw new ArgumentNullException(nameof(serviceProvider));
if (StaticResourceKey != null)
{
var staticResourceExtension = new StaticResourceExtension { Key = StaticResourceKey };
FontSize = (double)staticResourceExtension.ProvideValue(serviceProvider);
}
return Services.Sizing.FontSizeAdapter(FontSize);
}
}
用法可以是：
...
FontSize="{extension:FontSize StaticResourceKey=EntryFontSize}}"
...