如何将ListView按钮的绑定上下文设置为Xamarin Forms中父级的绑定上下文

Question

基本上,我有一个带有DataTemplate选择器的ListView,它使用基于ListView项的特定DataTemplate.

现在,在DataTemplate中 - 我有一个带有命令的按钮,应该在Parent(或ListView)本身的ViewModel上绑定.

请注意,我只想绑定按钮的Command属性,因为Text和其他属性需要绑定到按钮的当前绑定Context.

DataTemplate的BindingContext是ListView Item bindingContext(在本例中为Message Model),但我希望能够将数据模板中的特定按钮绑定到父listView的viewmodel.

我怎么做？

<?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="MobileMobile.Views.MobileMessageListView"
        Title="Message List"
        NavigationPage.BarBackgroundColor="#FF9100"
        NavigationPage.BarTextColor="White"
        xmlns:ViewSwitchers="clr-namespace:MobileMobile.ViewSwitchers;assembly=MobileMobile"
        xmlns:ViewCells="clr-namespace:MobileMobile.ViewCells;assembly=MobileMobile"
        xmlns:Extensions="clr-namespace:MobileMobile.Extensions;assembly=MobileMobile"
        >

    <ContentPage.Resources>
        <ResourceDictionary>
            <DataTemplate x:Key="botMessageDataTemplate">
                <ViewCell>
                    <Button Text="Hello!" Command="{Binding TestCommand, Source=???}" CommandParameter="Hello"/>
                </ViewCell>
            </DataTemplate>

            <ViewSwitchers:MobileMessageTemplateSwitcher x:Key="MobileMessageTemplateSwitcher" BotMessageDataTemplate="{StaticResource botMessageDataTemplate}" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <ContentPage.Content>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="Auto" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>

            <StackLayout Grid.Row="0" Orientation="Vertical" x:Name="MainViewStack">
                <ListView
                        CachingStrategy="RecycleElement"
                        BackgroundColor="Transparent"
                        ItemTemplate="{StaticResource MobileMessageTemplateSwitcher}"
                        IsPullToRefreshEnabled="true"
                        RefreshCommand="{Binding RefreshCommand}"
                        ItemsSource="{Binding Messages}"
                        HasUnevenRows="true"
                        IsRefreshing="{Binding IsLoading, Mode=OneWay}"
                        SeparatorVisibility="None">
                    <ListView.Footer/>
                </ListView>
            </StackLayout>
            <StackLayout Grid.Row="1" Orientation="Horizontal" HeightRequest="50">
                <Entry Text="{Binding CurrentMessageText}" Placeholder="{Binding MessageTextPlaceHolder}" HorizontalOptions="FillAndExpand"/>
                <Button Text="SEND" Command="{Binding SendMessageCommand}"/>
            </StackLayout>
        </Grid>
    </ContentPage.Content>
</ContentPage>

Answer 1

试试这个:

<Button
    Text="Hello!"
    Command="{Binding Path=BindingContext. TestCommand, Source={x:Reference Name=MessageListPage}}"
    CommandParameter="Hello" />

你将不得不给页面的x:Name与值属性MessageListPage,因此它可以与你的纯MVVM弄乱了一点,但因为Xamarin XAML不支持相对结合(据我所知..),这是要走的路.