LinearGradientBrush实验初始化问题

如何解决LinearGradientBrush实验初始化问题

您好，我在登录页面时遇到错误。我只是对Mainpage.xaml文件进行编码，其他文件是默认文件，因此在创建项目时选择了“空白”。 我的错误是：

“ system.invalidOperationException：”您尝试使用的类，属性或方法（“ GradientBrush”是GradientBrush的一部分；要使用它，必须在调用Forms.SetFlags（“ Brush_Experimental”）之前选择加入调用Forms.Init（）。”

我只写了一个文件Mainpage.xaml。有人帮我解决我的问题吗？

    <?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="HealthCareApp.MainPage">
<StackLayout>
        <StackLayout.Background>
            <LinearGradientBrush EndPoint="0,1">
                <GradientStop Color="#48b6a6" Offset="0.1" /> 
                <GradientStop Color="#2b78d4" Offset="1.0" />
            </LinearGradientBrush>
        </StackLayout.Background>
        <StackLayout Padding="0" Margin="10,100,10,0" HorizontalOptions="FillAndExpand" >
            <Frame BackgroundColor="Transparent" HeightRequest="500" Padding="0" Margin="0">
                <StackLayout>
                    <StackLayout Margin="10">
                        <Label Text="SIGN IN" TextColor="White" HorizontalOptions="CenterandExpand" FontAttributes="Bold" ></Label>
                    </StackLayout>
                    <StackLayout Padding="0" Margin="15,10">
                        
                        <Frame BackgroundColor="Transparent" BorderColor="White" Padding="0" HorizontalOptions="FillAndExpand" CornerRadius="30">
                            <StackLayout Orientation="Horizontal">
                                <Frame BackgroundColor="SkyBlue" HeightRequest="40" WidthRequest="40" CornerRadius="30" Padding="0" Margin="5">
                                    <Image Source="https://www.findool.com/images/avatars/avatar.png" Aspect="AspectFill" Margin="0"/>
                                </Frame>
                                <Entry Placeholder="Email" TextColor="#666666" FontAttributes="None" HorizontalOptions="FillAndExpand" Margin="0,20,0"/>
                            </StackLayout>
                        </Frame>

                        <Frame BackgroundColor="Transparent" BorderColor="White" Margin="0,15,0" Padding="0" HorizontalOptions="FillAndExpand" CornerRadius="30">
                            <StackLayout Orientation="Horizontal">
                                <Frame BackgroundColor="SkyBlue" HeightRequest="40" WidthRequest="40" CornerRadius="30" Padding="0" Margin="5">
                                    <Image Source="https://images.all-free-download.com/images/graphicthumb/lock_icon_6813906.jpg" Aspect="AspectFill" Margin="0"/>
                                </Frame>
                                <Entry Placeholder="Password" IsPassword="True" TextColor="White" FontAttributes="None" HorizontalOptions="FillAndExpand" Margin="0,0"/>
                            </StackLayout>
                        </Frame>

                        <StackLayout  Orientation="Horizontal">
                            <CheckBox IsChecked="False" Color="White" />
                            <Label Text="Remember me" TextColor="White" FontSize="Small" VerticalTextAlignment="Center" HorizontalTextAlignment="Center" />

                            <Label Text="Forgot Password" TextColor="White" FontAttributes="Bold" HorizontalOptions="EndAndExpand" FontSize="Small" VerticalTextAlignment="Center" HorizontalTextAlignment="Center" />
                        </StackLayout>

                        <Button Text="SIGN IN" BackgroundColor="#2b78d4" TextColor="White" CornerRadius="30" />
                        <StackLayout Orientation="Horizontal" HorizontalOptions="CenterandExpand">
                            <Label Text="Still Not Connected ?" TextColor="White" FontSize="Small"/>
                            <Label Text="Sign Up" TextColor="White" FontAttributes="Bold" FontSize="Small"/>
                        </StackLayout>

                        <StackLayout Margin="0,25,0" Padding="0">
                            <Grid>
                                <BoxView BackgroundColor="White" HeightRequest="1" WidthRequest="150"  HorizontalOptions="Center" VerticalOptions="Center"/>
                                <Frame BackgroundColor="White" HeightRequest="45" WidthRequest="45" CornerRadius="45" HasShadow="False" BorderColor="White" Margin="0" HorizontalOptions="Center" Padding="0">
                                    <Label Text="OR" TextColor="White" FontSize="Small" VerticalTextAlignment="Center" HorizontalTextAlignment="Center"/>
                                </Frame>
                            </Grid>
                        </StackLayout>

                        <StackLayout Margin="0,25" Orientation="Horizontal" HorizontalOptions="CenterandExpand">
                            <Frame BackgroundColor="White" HeightRequest="45" WidthRequest="45" CornerRadius="45" HasShadow="False" BorderColor="White" Margin="0" HorizontalOptions="Center" Padding="0">
                                <Image Source="https://www.pngitem.com/pimgs/m/44-440455_transparent-background-fb-logo-hd-png-download.png" Aspect="AspectFill" Margin="0"/>
                            </Frame>
                            <Frame BackgroundColor="White" HeightRequest="45" WidthRequest="45" CornerRadius="45" HasShadow="False" BorderColor="White" Margin="0" HorizontalOptions="Center" Padding="0">
                                <Image Source="https://blog.hubspot.com/hubfs/image8-2.jpg" Aspect="AspectFill" Margin="0"/>
                            </Frame>
                        </StackLayout>
                        
                    </StackLayout>
                </StackLayout>
            </Frame >    
        </StackLayout>
</StackLayout >

</ContentPage>

解决方法

根据documentation，您需要为开发团队仍处于试验阶段的某些功能设置实验性标志（在目标平台项目中），以便您在使用它们之前先确认一下。

在android上，您将在MainActivity类中，在ios上将在AppDelegate类中：

Forms.SetFlags("Brush_Experimental")

您可以一次设置多个实验标记，例如：

Xamarin.Forms.Forms.SetFlags(new string[] { "SwipeView_Experimental","Shapes_Experimental","AppTheme_Experimental" });

注意

请务必在SetFlags()之前致电Xamarin.Forms.Forms.Init()