Xamarin顯示DataTemplate中的一項-有解無憂

我正在嘗試在我的 Xamarin 應用程式中顯示一個帶有 DataTemplate 的專案，我可以使用什么 XAML 控制元件？

就我而言，我正在構建一個會議應用程式，并且正在嘗試顯示會議的所有者。
我嘗試使用 CollectionView（UserTemplate 是一個 DataTemplate）：

<CollectionView
            ItemsSource="{Binding Meeting.Owner}"
            ItemTemplate="{StaticResource UserTemplate}"/>

但這沒有顯示任何內容，因為 CollectionView 僅支持專案串列（當我嘗試使用串列時它確實有效）。
我可以為單個專案使用什么替代方案？

用戶模板 XAML：

<DataTemplate x:Key="UserTemplate">
    <Grid Padding="10"
          RowDefinitions="Auto,Auto"
          ColumnDefinitions="Auto,Auto">
        <Image Grid.RowSpan="2" 
               Source="{Binding IconURL}" 
               Aspect="AspectFill"
               HeightRequest="60" 
               WidthRequest="60" />
        <Label Grid.Column="1" 
               Text="{Binding Name}" 
               FontAttributes="Bold" />
        <Label Grid.Row="1"
               Grid.Column="1" 
               Text="{Binding age}"
               FontAttributes="Italic" 
               VerticalOptions="End" />
    </Grid>
</DataTemplate>

uj5u.com熱心網友回復：

我知道這可能不是一個完美的解決方案，但也許它會幫助你。

您可以使用 ContentView 來顯示您的資料，而不是模板。XML 看起來幾乎與您的模板相似。

XAML：

<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             xmlns:models="clr-namespace:TestAppNew.Models"
             x:Class="TestAppNew.Views.UserView"
             x:Name="View">

    <Frame BindingContext="{Binding Source={x:Reference View}, Path=User}" 
           x:DataType="models:User">
        <Grid Padding="10"
              RowDefinitions="Auto,Auto"
              ColumnDefinitions="Auto,Auto">

            <Label Grid.Column="1" 
                   Text="{Binding Name}" 
                   FontAttributes="Bold" />

            <Label Grid.Row="1"
                   Grid.Column="1" 
                   Text="{Binding age}"
                   FontAttributes="Italic" 
                   VerticalOptions="End" />
        </Grid>
    </Frame>
</ContentView>

背后的代碼：

    public partial class UserView : ContentView, INotifyPropertyChanged
    {
        #region INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            var changed = PropertyChanged;
            if (changed == null)
                return;

            changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion

        public User User
        {
            get => (User)GetValue(UserProperty);
            set => SetValue(UserProperty, value);
        }

        public static readonly BindableProperty UserProperty =
            BindableProperty.Create("User", typeof(User), typeof(UserView), new User(),
                propertyChanged: (bindable, oldVal , newVal) => ((UserView)bindable).OnPropertyChanged(nameof(User)));


        public UserView()
        {
            InitializeComponent();
        }
    }

現在您可以在您的代碼中使用此視圖。

單品：

<views:UserView User="{Binding Meeting.Owner}" />

或多個：

<CollectionView ItemsSource="{Binding Meetings}">
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <views:UserView User="{Binding Owner}" />
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

無需做進一步研究，我認為您應該能夠將此視圖包裝在額外的 DataTemplate 中，以便您仍然可以訪問 ListView 或 CollectionView 的直接 ItemTemplate 屬性

uj5u.com熱心網友回復：

給定一個Meeting，包含一個屬性User，我們怎么能顯示DataTemplate的Meeting.User？

要使用CollectionView，我們需要一個List<User>. 一種解決方案是創建一個“價值轉換器”：

using System;
using System.Collections.Generic;
using System.Globalization;
using Xamarin.Forms;

namespace BindSubView
{
    /// <summary>
    /// Given a single object, return a list containing just that object.
    /// </summary>
    public class OneItemListConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return new List<object> { value };
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

用法示例：

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                 xmlns:local="clr-namespace:BindSubView"
                 x:Class="BindSubView.MainPage">
    <ContentPage.BindingContext>
        <local:MainPageViewModel/>
    </ContentPage.BindingContext>
    <ContentPage.Resources>
        <ResourceDictionary>
            <local:OneItemListConverter x:Key="oneItemList" />
        </ResourceDictionary>
    </ContentPage.Resources>
    <StackLayout>
        <CollectionView ItemsSource="{Binding Meeting.User, Converter={StaticResource oneItemList}}" HeightRequest="100">
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <StackLayout>
                        <Label Text="{Binding Name}"/>
                        <Label Text="{Binding SomeProperty}"/>
                    </StackLayout>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    </StackLayout>
</ContentPage>

我已經展示了一個 inline DataTemplate，但這可以使用在別處定義的 DataTemplate ：

<CollectionView ... ItemTemplate="{StaticResource YourTemplateName}"/>

以上回答使用的定義MainPageViewModel，Meeting以及User如下圖所示。

或如果目標是在另一個屬性（會議）上顯示屬性（用戶）的詳細資訊，則可能根本不需要 DataTemplate。

This is a different goal than the question asked; this shows how to refer to "nested" properties such as "Meeting.User.Name".

Consider these models:

using Xamarin.Forms;

namespace BindSubView
{
    public class Meeting : BindableObject
    {
        public string Description { get; set; } = "Description of meeting";
        public User User { get; set; } = new User();
    }

    public class User : BindableObject
    {
        public string Name { get; set; } = "Test User";
        public string SomeProperty { get; set; } = "Test SomeProperty";
    }
}

: BindableObject is optional; it is for use (later in development) of the convenience method OnPropertyChanged(nameof(SomeProperty));

And this view model:

public class MainPageViewModel : BindableObject
{
    public Meeting Meeting { get; set; } = new Meeting();
}

Two possible approaches.

-1. Refer directly to "nested" properties. E.g. {Binding Meeting.User.Name}:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:BindSubView"
             x:Class="BindSubView.MainPage">
    <ContentPage.BindingContext>
        <local:MainPageViewModel/>
    </ContentPage.BindingContext>
    <StackLayout>
        <Label Text="{Binding Meeting.Description}"/>
        <StackLayout>
            <Label Text="{Binding Meeting.User.Name}"/>
            <Label Text="{Binding Meeting.User.SomeProperty}"/>
        </StackLayout>
    </StackLayout>
</ContentPage>

OR 2. Set a different "BindingContext" on parts of the XAML.

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:BindSubView"
             x:Class="BindSubView.MainPage">
    <ContentPage.BindingContext>
        <local:MainPageViewModel/>
    </ContentPage.BindingContext>
    <!-- "Meeting" refers to a Property on the enclosing BindingContext. Here it means "MainPageViewModel.Meeting". -->
    <StackLayout BindingContext="{Binding Meeting}">
        <Label Text="{Binding Description}"/>
        <!-- "User" refers to a Property on the enclosing BindingContext. Here it means "MainPageViewModel.Meeting.User". -->
        <StackLayout BindingContext="{Binding User}">
            <Label Text="{Binding Name}"/>
            <Label Text="{Binding SomeProperty}"/>
        </StackLayout>
    </StackLayout>
</ContentPage>

These two XAML snippets behave identically. Both display:

Description of meeting

Test User

Test SomeProperty

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標籤：xml 沙马林 xamarin.forms

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