Xamarin.Forms DataTemplateSelector在iOS上不起作用(未调用构造函数) [英] Xamarin.Forms DataTemplateSelector doesnt work on iOS (Constructor not called)

问题描述

我正在像这样夸大数据模板选择器:

I am inflating a data template selector like so:

<ContentPage.Resources>
    <ResourceDictionary>
        <local:MyDataTemplateSelector x:Key="templateSelector"></local:MyDataTemplateSelector>
    </ResourceDictionary>
</ContentPage.Resources>

            <Grid Grid.Row="0"   >

                <abstractions:CarouselViewControl VerticalOptions="Start"  x:Name="carouselview" ItemTemplate="{StaticResource templateSelector}" />

            </Grid>

代码如下:

    public MyDataTemplateSelector()
    {
        Layout1 = new DataTemplate(typeof(CV_CarouselView_ShowPics));
        Layout2 = new DataTemplate(typeof(CV_VideoPlayer));
    }

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        FullAdType cell = (FullAdType)item;

        if(cell != null && cell.hasVideo )
        {

            return Layout2; // get video layout 

        }

        else
            return Layout1;

    }

但是在iOS上都不会调用任何数据模板选择器构造函数，但在Android上，都可以正常工作.

But neither of the data template selectors constructors is called on iOS but on Android, it works just fine.

这是什么问题?

谢谢

推荐答案

我们经常在xaml中定义 DataTemplate ，

We often define the DataTemplate in xaml ,check here .

 <ContentPage.Resources>
        <DataTemplate x:Key="AmericanMonkeyTemplate">
            ...
        </DataTemplate>

        <DataTemplate x:Key="OtherMonkeyTemplate">
            ...
        </DataTemplate>

        <controls:MonkeyDataTemplateSelector x:Key="MonkeySelector"
                                             AmericanMonkey="{StaticResource AmericanMonkeyTemplate}"
                                             OtherMonkey="{StaticResource OtherMonkeyTemplate}" />
    </ContentPage.Resources>

    <CarouselView ItemsSource="{Binding Monkeys}"
                  ItemTemplate="{StaticResource MonkeySelector}" />

---

但是，如果要在后面的代码中初始化DataTemplate，则可以在数据模板选择器构造函数中创建它们.

---

However , if you want to initialize DataTemplate in code behind, you can create them in data template selector constructor .

public PersonDataTemplateSelector()
        {
            ValidTemplate = new DataTemplate(()=> {

                var grid = new Grid();

                var nameLabel = new Label { FontAttributes = FontAttributes.Bold };
                nameLabel.TextColor = Color.Green;
                nameLabel.SetBinding(Label.TextProperty, "Name");
                grid.Children.Add(nameLabel);

                return grid ;
            });

            InvalidTemplate = new DataTemplate(() => {

                var grid = new Grid();

                var nameLabel = new Label {  };
                nameLabel.TextColor = Color.Red;
                nameLabel.SetBinding(Label.TextProperty, "Name");
                grid.Children.Add(nameLabel);

                return grid ;
            });

        }

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