Xamarin Forms 扩展器 在扩展事件中？

Question

I am using an Expander in Xamarin.Forms

<xct:Expander PropertyChanging="Expander_PropertyChanging" PropertyChanged="Expander_PropertyChanged">

I am wondering if there is an event for when the expander is showing the hidden section (on expanding)

I can see that Expander has these 2 events (PropertyChanging and PropertyChanged)

void Expander_PropertyChanging(System.Object sender, Xamarin.Forms.PropertyChangingEventArgs e)
        {
        }

        void Expander_PropertyChanged(System.Object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
        }

However these run every second, even when I am not expanding, What I am looking for is away for when I am expanding, call a method once.

Answer 1

You can use the Command method in Expander.

This method will be triggered every time the user clicks to expand or hide.

Here is the xaml code:

<StackLayout>
    <xct:Expander Command="{Binding myTest}">
        <!-- Use the Command method above -->
        <xct:Expander.Header>
            <Label Text="Baboon"
               FontAttributes="Bold"
               FontSize="Medium" />
        </xct:Expander.Header>
        <Grid Padding="10">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition Width="Auto" />
            </Grid.ColumnDefinitions>
            <Image Source="http://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/Papio_anubis_%28Serengeti%2C_2009%29.jpg/200px-Papio_anubis_%28Serengeti%2C_2009%29.jpg"
               Aspect="AspectFill"
               HeightRequest="120"
               WidthRequest="120" />
            <Label Grid.Column="1"
               Text="Baboons are African and Arabian Old World monkeys belonging to the genus Papio, part of the subfamily Cercopithecinae."
               FontAttributes="Italic" />
        </Grid>
    </xct:Expander>
</StackLayout>

Add xmlns:xct="http://xamarin.com/schemas/2020/toolkit" in the ContentPage tag. Here is the background code:

public ICommand myTest { set; get; }
public MainPage()
{
    InitializeComponent();
    myTest = new Command(() => Console.WriteLine("Command executed"));
    BindingContext = this;
}

The myTest method will be triggered every time the user expands or hides.