在Xamarin表单中将DataTemplate用于Listview时，CommandParameter提供空值

问题描述

我在CommandParameter中遇到问题，该参数在listView的DataTemplate中.我为ListView使用了单独的DataTemplate，并且单击listView中的图像时，无法在commandParameter中传递图像路径.

I'm facing issue in CommandParameter which is in DataTemplate for the listView.I have separate DataTemplate for ListView and i am not able to pass the imagepath in the commandParameter when click on image in the listView.

 <?xml version="1.0" encoding="utf-8" ?>

xmlns:local ="clr-namespace:RCBazaar.Localization" xmlns:template ="clr-namespace:RCBazaar.Views.Templates" xmlns:cards ="clr-namespace:PanCardView; assembly = PanCardView" xmlns:controls ="clr-namespace:PanCardView.Controls; assembly = PanCardView" x:Class ="RCBazaar.Views.HomeView"填充="0" x:Name ="HomePage"> </样式> </ResourceDictionary> </ContentPage.Resources>->

xmlns:local="clr-namespace:RCBazaar.Localization" xmlns:template="clr-namespace:RCBazaar.Views.Templates" xmlns:cards="clr-namespace:PanCardView;assembly=PanCardView" xmlns:controls="clr-namespace:PanCardView.Controls;assembly=PanCardView" x:Class="RCBazaar.Views.HomeView" Padding="0" x:Name="HomePage"> </Style> </ResourceDictionary> </ContentPage.Resources>-->

<ContentPage.Content>

    <Grid  Style="{StaticResource MainGrid}">
        <Grid.RowDefinitions>
            <RowDefinition  Height="140"></RowDefinition>
            <RowDefinition  Height="Auto"></RowDefinition>
            <RowDefinition  Height="*"  ></RowDefinition>
        </Grid.RowDefinitions>

        <cards:CarouselView  Margin="0"  x:Name="carousel" Grid.Row="0"  ItemsSource="{Binding ProductImage,Mode=TwoWay}" >
            <cards:CarouselView.ItemTemplate>
                <DataTemplate>
                    <ffimageloading:CachedImage HorizontalOptions="FillAndExpand" Source="{Binding ImageName}" Style="{StaticResource CachedImageStyle}">
                    </ffimageloading:CachedImage>
                </DataTemplate>
            </cards:CarouselView.ItemTemplate>
            <controls:IndicatorsControl ToFadeDuration="1500"  BackgroundColor="Gray"/>
            <controls:LeftArrowControl  ToFadeDuration="2500" BackgroundColor="Gray" />
            <controls:RightArrowControl ToFadeDuration="2500" BackgroundColor="Gray"/>
        </cards:CarouselView>



        <Image Grid.Row="1" Margin="0,0,10,0" Source="ic_sort.png" HeightRequest="30" WidthRequest="30"  HorizontalOptions="EndAndExpand">
            <Image.GestureRecognizers>
                <TapGestureRecognizer Command="{Binding SortPopupCommand}"/>
            </Image.GestureRecognizers>
        </Image>

        <ListView IsEnabled="True"  HeightRequest="{Binding ListHeight}"  CachingStrategy="RecycleElement" x:Name="mylist" Style="{StaticResource ListviewStyle}" Grid.Row="2" SelectedItem="{Binding SelectedProduct,Mode=TwoWay}"  ItemsSource="{Binding HomeProducts}" >
            <ListView.Behaviors>
                <behaviors:EventToCommandBehavior EventName="ItemSelected"   Command="{Binding HomeProductSelectedCommand}"></behaviors:EventToCommandBehavior>
            </ListView.Behaviors>
            <ListView.ItemTemplate>
                <DataTemplate>
                    <template:ProductCell ParentBindingContext="{Binding Source={x:Reference mylist}, Path=BindingContext}"/>

                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>


        <ActivityIndicator Grid.Row="2"  VerticalOptions="Start"   IsVisible="{Binding IsBusy,Mode=TwoWay}" IsRunning="{Binding IsBusy,Mode=TwoWay}" Color="Blue"/>

    </Grid>

</ContentPage.Content>

<ViewCell.View>
    <Grid   RowSpacing="5" Style="{StaticResource ProductTemplateGrid}"  >
        <Grid.RowDefinitions>
            <RowDefinition Height="28*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="40*"/>
            <ColumnDefinition Width="60*"/>
        </Grid.ColumnDefinitions>

        <ffimageloading:CachedImage  x:Name="img" VerticalOptions="FillAndExpand" Style="{StaticResource CachedImageStyle}" Aspect="AspectFit"  Grid.Row="0" Source="{Binding PictureBinary,Converter={StaticResource Base64StringToImageConverter}}" Grid.RowSpan="5" Grid.Column="0">
            <ffimageloading:CachedImage.GestureRecognizers>

                <TapGestureRecognizer BindingContext="{Binding Source={x:Reference mylist}, Path=ParentBindingContext}" Command="{Binding ViewImageCommand}" CommandParameter="{Binding PictureBinary}"/>
            </ffimageloading:CachedImage.GestureRecognizers>
        </ffimageloading:CachedImage>


        <Label Grid.Row="0"  Grid.Column="1" MaxLines="2" LineBreakMode="TailTruncation"  Style="{StaticResource lblDarkBody}"  Text="{Binding Name}" ></Label>

        <Label Grid.Row="1" Grid.Column="1" Text="{local:Translate SKU}" Style="{StaticResource lblNormal}"></Label>
        <Label Margin="35,0,0,0" Grid.Row="1" Grid.Column="1" Text="{Binding upc}" Style="{StaticResource lblNormal}"    />

        <Label Grid.Row="2" Grid.Column="1" Text="{local:Translate Stock}"  Style="{StaticResource lblNormal}" VerticalOptions="Center" ></Label>
        <Image Margin="45,0,0,0" Grid.Row="2" Grid.Column="1" VerticalOptions="Center" HorizontalOptions="StartAndExpand" Source="{Binding qtyonhand,Converter={StaticResource QuantityToColorConverter}}" />

        <uc:CustomRatingBar  Grid.Row="3" Grid.Column="1"  Style="{StaticResource RatingsStyle}"     x:Name="CusRatingBar"  Rating="{Binding RatingSum}" />

        <Image Grid.Row="4" Grid.Column="1"  Source="in.png" HorizontalOptions="Start" VerticalOptions="Center"/>
        <Label Margin="30,0,0,0"  Grid.Row="4" Grid.Column="1" VerticalOptions="Center" Style="{StaticResource lblEmphasis}"  Text="{Binding pricelist,StringFormat='Rs {0:#,0.#0}'}" ></Label>

        <Image Grid.Row="4" Grid.Column="1" Margin="0,0,10,0" WidthRequest="30" HeightRequest="30" VerticalOptions="Center"  Style="{StaticResource StockCachedImageStyle}"  Source="heartdark.png"  HorizontalOptions="End">

            <Image.GestureRecognizers>
                <TapGestureRecognizer BindingContext="{Binding Source={x:Reference mylist}, Path=ParentBindingContext}"  Command="{Binding AddtoWishlistCommand}" CommandParameter="{Binding .}" />
            </Image.GestureRecognizers>
        </Image>

    </Grid>
</ViewCell.View>

推荐答案

如果您在XAML中为有问题的页面提供x:Name，则可以引用原始BindingContext(应为ViewModel)，同时还可以访问该项目本身作为commandContext的BindingContext.看起来像这样:

If you give the page in question an x:Name in your XAML you can then refer to the origional BindingContext (should be your ViewModel) while also having access to the item itself as BindingContext for the commandparameter. Looks something like this:

<ContentPage x:Name="MyContentPage"
....
<!--inside your DataTemple you can now reference the BindingContext of your page-->
Command="{Binding Path=BindingContext.HomeProductSelectedCommand, Source={x:Reference MyContentPage}} CommandParameter="{Binding .}"
…

此示例将项目的绑定上下文(默认情况下为项目本身)传递给命令参数

This example passes the bindingcontext of the item (by default that's the item itself) to the command parameter

这篇关于在Xamarin表单中将DataTemplate用于Listview时，CommandParameter提供空值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！