Xamarin Forms CollectionView绑定后仍然保持为空。

huangapple
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英文:

Xamarin Forms CollectionView stays empty after binding it

问题

我有一个问题。我创建了一个创建ImageSource集合ObservableCollection<TemplateSource>的类：

  1. public class TemplateListViewModel
  2. {
  3.     public ObservableCollection<TemplateSource> sourceList { get; set; }
  5.     public TemplateListViewModel()
  6.     {
  7.         sourceList = new ObservableCollection<TemplateSource>();
  8.         loadingTemplates += onLoadingTemplates;
  9.         LoadTemplateList();
  10.     }
  12.     private event EventHandler loadingTemplates = delegate { };
  14.     private void LoadTemplateList()
  15.     {
  16.         loadingTemplates(this, EventArgs.Empty);
  17.     }
  19.     private async void onLoadingTemplates(object sender, EventArgs args)
  20.     {
  21.         List<Template> templateList = await App.RestService.GetTemplates(App.User);
  23.         foreach (var template in templateList)
  24.         {
  25.             ImageSource source = ImageSource.FromUri(new Uri("mysite.org/myapp/" + template.FileName));
  26.             TemplateSource templateSource = new TemplateSource { Id = template.Id, Source = source };
  27.             sourceList.Add(templateSource);
  28.         }
  29.     }
  30. }

在我的XAML中，我使用以下代码：

  1. <ContentPage.Content>
  2.     <StackLayout HorizontalOptions="Fill">
  3.         <Frame IsClippedToBounds="True" HeightRequest="45" CornerRadius="5" Padding="0" Margin="15,15,15,0" BackgroundColor="Transparent">
  4.             <Entry Placeholder="Search" ReturnType="Done" PlaceholderColor="Gray" x:Name="txtSearch" Margin="5,0,0,0" TextColor="White" />
  5.         </Frame>
  7.         <CollectionView ItemsLayout="HorizontalList" ItemsSource="{Binding sourceList}">
  8.             <CollectionView.ItemTemplate>
  9.                 <DataTemplate>
  11.                     <ff:CachedImage
  12.                 Source="{Binding .}"
  13.                 VerticalOptions="Center"
  14.                 HorizontalOptions="Fill" />
  16.                 </DataTemplate>
  17.             </CollectionView.ItemTemplate>
  18.         </CollectionView>
  19.     </StackLayout>
  20. </ContentPage.Content>

最后，在page.xaml.cs（代码后台）中：

  1. protected override void OnAppearing()
  2. {
  3.     TemplateListViewModel vm = new TemplateListViewModel();
  4.     BindingContext = vm;
  5.     base.OnAppearing();
  6. }

现在我已经从@Deczaloth得到了关于这段代码的帮助，但他无法弄清楚为什么绑定后CollectionView仍然为空。现在我已经检查过了，但sourceList确实被填充了，所以这不是问题。

我做错了什么？

英文:

I have a problem. I created this class that creates an ImageSource collection ObservableCollection&lt;TemplateSource&gt;:

  1. public class TemplateListViewModel
  2. {
  3.     public ObservableCollection&lt;TemplateSource&gt; sourceList { get; set; }
  5.     public TemplateListViewModel()
  6.     {
  7.         sourceList = new ObservableCollection&lt;TemplateSource&gt;();
  8.         loadingTemplates += onLoadingTemplates;
  9.         LoadTemplateList();
  10.     }
  12.     private event EventHandler loadingTemplates = delegate { };
  14.     private void LoadTemplateList()
  15.     {
  16.         loadingTemplates(this, EventArgs.Empty);
  17.     }
  19.     private async void onLoadingTemplates(object sender, EventArgs args)
  20.     {
  21.         List&lt;Template&gt; templateList = await App.RestService.GetTemplates(App.User);
  23.         foreach (var template in templateList)
  24.         {
  25.             ImageSource source = ImageSource.FromUri(new Uri(&quot;mysite.org/myapp/&quot; + template.FileName));
  26.             TemplateSource templateSource = new TemplateSource { Id = template.Id, Source = source };
  27.             sourceList.Add(templateSource);
  28.         }
  29.     }
  30. }

And in my XAML I use this code:

  1. &lt;ContentPage.Content&gt;
  2.     &lt;StackLayout HorizontalOptions=&quot;Fill&quot;&gt;
  3.         &lt;Frame IsClippedToBounds=&quot;True&quot; HeightRequest=&quot;45&quot; CornerRadius=&quot;5&quot; Padding=&quot;0&quot; Margin=&quot;15,15,15,0&quot; BackgroundColor=&quot;Transparent&quot;&gt;
  4.             &lt;Entry Placeholder=&quot;Search&quot; ReturnType=&quot;Done&quot; PlaceholderColor=&quot;Gray&quot; x:Name=&quot;txtSearch&quot; Margin=&quot;5,0,0,0&quot; TextColor=&quot;White&quot; /&gt;
  5.         &lt;/Frame&gt;
  7.         &lt;CollectionView ItemsLayout=&quot;HorizontalList&quot; ItemsSource=&quot;{Binding sourceList}&quot;&gt;
  8.             &lt;CollectionView.ItemTemplate&gt;
  9.                 &lt;DataTemplate&gt;
  11.                     &lt;ff:CachedImage
  12.                 Source=&quot;{Binding .}&quot;
  13.                 VerticalOptions=&quot;Center&quot;
  14.                 HorizontalOptions=&quot;Fill&quot; /&gt;
  16.                 &lt;/DataTemplate&gt;
  17.             &lt;/CollectionView.ItemTemplate&gt;
  18.         &lt;/CollectionView&gt;
  19.     &lt;/StackLayout&gt;
  20. &lt;/ContentPage.Content&gt;

And finally in the page.xaml.cs (code behind):

  1. protected override void OnAppearing()
  2. {
  3.     TemplateListViewModel vm = new TemplateListViewModel();
  4.     BindingContext = vm;
  5.     base.OnAppearing();
  6. }

Now I already got help with this code from @Deczaloth, but he couldn't figure out why the CollectionView stays emtpy after I bind it. Now I already checked, but the sourceList does get filled, so thats not the problem.

What am I doing wrong?

答案1

得分: 0

I can see one potential problem in your code XD:

当你绑定CachedImage的Source属性时，你将绑定设置为&quot;.&quot;，但你应该绑定到TemplateSource类的Source属性（在你的上下文中&quot;.&quot;表示一个TemplateSource项！），你应该像这样更改你的代码：

  1. <ff:CachedImage
  2.     Source="{Binding Source}"
  3.     VerticalOptions="Center"
  4.     HorizontalOptions="Fill" />
英文:

I can see one potential problem in your code XD:

When you bind the Source property of CachedImage you set the binding to &quot;.&quot;, but you should instead bind to the Source property of the TemplateSource class (in your context "." means a TemplateSource item!), that is you should change your code like so:

  1. &lt;ff:CachedImage
  2.     Source=&quot;{Binding Source}&quot;
  3.     VerticalOptions=&quot;Center&quot;
  4.     HorizontalOptions=&quot;Fill&quot; /&gt;

huangapple
  • 本文由 发表于 2020年1月7日 00:26:15
  • 转载请务必保留本文链接：https://go.coder-hub.com/59615591.html
  • c#
  • xamarin
  • xamarin.android
  • xamarin.forms
  • xamarin.ios
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