如何解决Xamarin Forms MacOS不能使用Expander吗？
我正在尝试实施Xamarin团队在MacOS上发布的新添加的Expander。
我正在遵循本指南：Xamarin Forms: How to set a list of items as the Expander Child?
<StackLayout x:Name="expanderLayout" IsVisible="False" BindableLayout.ItemsSource="{Binding AllItems,Mode=TwoWay}">
<BindableLayout.ItemTemplate>
<DataTemplate>
<Expander
ExpandAnimationEasing="{x:Static Easing.CubicIn}"
ExpandAnimationLength="500"
CollapseAnimationEasing="{x:Static Easing.CubicOut}"
CollapseAnimationLength="500">
<Expander.Header>
<Frame
Padding="2"
Margin="5"
HasShadow="False"
BorderColor="#fdeec7"
CornerRadius="0">
<StackLayout
HorizontalOptions="FillAndExpand"
VerticalOptions="FillAndExpand"
Orientation="Horizontal">
<Label
Text="{Binding unit.title}"
TextColor="Black"
HorizontalOptions="Start"
HorizontalTextAlignment="Start"
VerticalTextAlignment="Center"
VerticalOptions="CenterandExpand">
<Label.FontSize>
<OnIdiom x:TypeArguments="x:Double">
<OnIdiom.Phone>18</OnIdiom.Phone>
<OnIdiom.Tablet>36</OnIdiom.Tablet>
<OnIdiom.Desktop>18</OnIdiom.Desktop>
</OnIdiom>
</Label.FontSize>
</Label>
<StackLayout.Margin>
<OnIdiom x:TypeArguments="Thickness">
<OnIdiom.Phone>5</OnIdiom.Phone>
<OnIdiom.Tablet>8</OnIdiom.Tablet>
<OnIdiom.Desktop>5</OnIdiom.Desktop>
</OnIdiom>
</StackLayout.Margin>
<StackLayout.Padding>
<OnIdiom x:TypeArguments="Thickness">
<OnIdiom.Phone>5</OnIdiom.Phone>
<OnIdiom.Tablet>8</OnIdiom.Tablet>
<OnIdiom.Desktop>5</OnIdiom.Desktop>
</OnIdiom>
</StackLayout.Padding>
</StackLayout>
</Frame>
</Expander.Header>
<Expander.ContentTemplate>
<DataTemplate>
<StackLayout BindableLayout.ItemsSource="{Binding contentList,Mode=TwoWay}">
<BindableLayout.ItemTemplate>
<DataTemplate>
<StackLayout
Orientation="Horizontal">
<Label
HorizontalOptions="Start"
Text="{Binding title}"
VerticalOptions="CenterandExpand"
TextColor="Black">
<Label.FontSize>
<OnIdiom x:TypeArguments="x:Double">
<OnIdiom.Phone>16</OnIdiom.Phone>
<OnIdiom.Tablet>32</OnIdiom.Tablet>
<OnIdiom.Desktop>16</OnIdiom.Desktop>
</OnIdiom>
</Label.FontSize>
<Label.GestureRecognizers>
<TapGestureRecognizer
Tapped="LoadChapter"
CommandParameter="{Binding .}"
NumberOfTapsrequired="1">
</TapGestureRecognizer>
</Label.GestureRecognizers>
</Label>
</StackLayout>
</DataTemplate>
</BindableLayout.ItemTemplate>
</StackLayout>
</DataTemplate>
</Expander.ContentTemplate>
</Expander>
</DataTemplate>
</BindableLayout.ItemTemplate>
</StackLayout>
在导航到带有此代码的页面时，出现异常，表明我需要调用Xamarin.Forms.Forms.SetFlags("Expander_Experimental");，我已经在MacOS文件夹的public AppDelegate()方法中添加了该变量。
public AppDelegate()
{
Xamarin.Forms.Forms.SetFlags("Expander_Experimental");
Xamarin.Forms.Forms.SetFlags("CarouselView_Experimental");
var style = NSWindowStyle.Closable | NSWindowStyle.Miniaturizable | NSWindowStyle.Resizable | NSWindowStyle.Titled | NSWindowStyle.FullSizeContentView;
var frame = NSScreen.MainScreen.Frame;
var rect = NSWindow.FrameRectFor(frame,style);
_window = new NSWindow(rect,style,NSbackingStore.Buffered,false);
_window.MinSize = new CoreGraphics.CGSize(400,300);
_window.TitlebarappearsTransparent = true;
_window.MovableByWindowBackground = true;
_window.AccessibilityMinimized = false;
}
MacOS不支持扩展器，还是我错过了关键步骤？
我还尝试将其添加到DidFinishLaunching方法中，但没有区别。
public override void DidFinishLaunching(NSNotification notification)
{
Xamarin.Forms.Forms.SetFlags("Expander_Experimental");
Xamarin.Forms.Forms.SetFlags("CarouselView_Experimental");
Forms.Init();
CachedImageRenderer.Init();
...
解决方法
我在测试这个新组件时几乎碰到了它！如Xamarin.Forms experimental flags页上所述：
请不要多次调用
SetFlags方法，因为后续调用将覆盖先前调用的结果。
所以代替：
Xamarin.Forms.Forms.SetFlags("Expander_Experimental");
Xamarin.Forms.Forms.SetFlags("CarouselView_Experimental"); // This call overwrites the `Expander_Experimental` flag set just above
调用一次，但同时带有两个标志：
Xamarin.Forms.Forms.SetFlags(new string[] { "Expander_Experimental","CarouselView_Experimental" } );
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