如何跟踪模型属性的更改

huangapple
go评论91阅读模式
英文:

How to track changes of a property of a model

问题

我有一个模型上的这些属性。

  1. public class Student : BindableBase
  2. {
  3.     public Guid Id { get; set; }
  4.     public string Fullname { get; set; }
  5.     
  6.     private bool _isSelected;
  7.     public bool IsSelected { get => _isSelected; set => SetProperty(ref _isSelected, value); }
  8. }

在我的ViewModel中，基本上加载所有的学生并将其分配到集合中。

  1. public ObservableRangeCollection<Student> Students { get; } = new();
  2. private List<Guid> SelectedIds { get; set; }
  4. public override async Task OnActivatedAsync()
  5. {
  6.     var results = await _service.GetAllStudents(take: 100);
  7.     Students.ReplaceRange(results);
  8. }

在我的XAML中，

  1. <CollectionView ItemsSource="{x:Binding Students}">
  2.     <CollectionView.ItemTemplate>
  3.         <DataTemplate x:DataType="vm:Student">
  4.             <StackLayout>
  5.                 <StackLayout Margin="0,20" Orientation="Horizontal">
  6.                     <CheckBox IsChecked="{x:Binding IsSelected}" />
  7.                     <StackLayout>
  8.                         <Label
  9.                             FontAttributes="Bold"
  10.                             FontSize="17"
  11.                             Text="{x:Binding Fullname}"
  12.                             TextColor="{x:StaticResource ColorBlack}"
  13.                             VerticalOptions="Center" />
  14.                     </StackLayout>
  15.                 </StackLayout>
  16.                 <BoxView HeightRequest="1" Color="Gray" />
  17.             </StackLayout>
  18.         </DataTemplate>
  19.     </CollectionView.ItemTemplate>
  20. </CollectionView>

现在我想要实现的是，每当我选择一个项目时，我希望它立即添加到一个新的List<Guid>对象中。但目前我不知道如何做到这一点。

任何帮助都会非常感激。

提前致谢。

我可以使用Linq来检查哪些学生的IsSelected属性为true，但这是在保存按钮时进行的。但是我现在想做的是在选中和取消选中时将其添加/移除到一个新的List<Guid>对象中，我在如何实现这个过程中遇到了困难。

英文:

I have this properties on my model.

  1. public class Student : BindableBase
  2. {
  3. 	 public Guid Id { get; set; }
  4. 	 public string Fullname { get; set; }
  5. 	 
  6. 	 private bool _isSelected;
  7. 	 public bool IsSelected { get =&gt; _isSelected; set =&gt; SetProperty(ref _isSelected, value); }
  8. }

And in my ViewModel basically loads all the students and assigned it into the Collection.

  1. public ObservableRangeCollection&lt;Student&gt; Students { get; } = new();
  2. private List&lt;Guid&gt; SelectedIds { get; set; }
  4. public override async Task OnActivatedAsync()
  5. {
  6. 	 var results = await _service.GetAllStudents(take: 100);
  7. 	 Students.ReplaceRange(results);
  8. }

And in my Xaml

  1. &lt;CollectionView ItemsSource=&quot;{x:Binding Students}&quot;&gt;
  2. 	&lt;CollectionView.ItemTemplate&gt;
  3. 		&lt;DataTemplate x:DataType=&quot;vm:Student&quot;&gt;
  4. 			&lt;StackLayout&gt;
  5. 				&lt;StackLayout Margin=&quot;0,20&quot; Orientation=&quot;Horizontal&quot;&gt;
  6. 					&lt;CheckBox IsChecked=&quot;{x:Binding IsSelected}&quot; /&gt;
  7. 					&lt;StackLayout&gt;
  8. 						&lt;Label
  9. 							FontAttributes=&quot;Bold&quot;
  10. 							FontSize=&quot;17&quot;
  11. 							Text=&quot;{x:Binding Fullname}&quot;
  12. 							TextColor=&quot;{x:StaticResource ColorBlack}&quot;
  13. 							VerticalOptions=&quot;Center&quot; /&gt;
  14. 					&lt;/StackLayout&gt;
  15. 				&lt;/StackLayout&gt;
  16. 				&lt;BoxView HeightRequest=&quot;1&quot; Color=&quot;Gray&quot; /&gt;
  17. 			&lt;/StackLayout&gt;
  18. 		&lt;/DataTemplate&gt;
  19. 	&lt;/CollectionView.ItemTemplate&gt;
  20. &lt;/CollectionView&gt;

Now what I want to achieve is that whenever I select an item I want it to be added to a new List of items object right away. But for now I don't have an idea how to do such thing.

Any help is much appreciated.

Thanks in advance

I can check who among of the students that has IsSelected = true by using Linq but this is during Save button. But what I wanted to do now is during check and uncheck it is being added/remove in a new List<Guid> object, which is I'm having a hard time how to implement.

答案1

得分: 1

你必须将CollectionView的SelectedItem属性绑定到模型中的属性：

  1. <CollectionView ItemsSource="{Binding View}" SelectedItem="{Binding SelectedItem, Mode=TwoWay}">

以及模型中的属性：

  1. public Student SelectedItem
  2. {
  3.     get
  4.     {
  5.         return selectedItem;
  6.     }
  7.     set
  8.     {
  9.         selectedItem = value;
  10.         DoSomeActionWithSelectedItem(selectedItem);
  11.     }
  12. }
  13. private Student selectedItem;
  15. private void DoSomeActionWithSelectedItem(Student student)
  16. {
  17.     // 在函数 'DoSomeActionWithSelectedItem' 中，你可以将学生添加到列表等等。
  18.     // .....
  19. }
英文:

You must binding property 'SelectedItem' of CollectionView to property in model:

  1. &lt;CollectionView ItemsSource=&quot;{Binding View}&quot; SelectedItem=&quot;{Binding&gt; SelectedItem, Mode=TwoWay}&quot;&gt;

And property in model:

  1. public Student SelectedItem  
  2. {   
  3.    get 
  4.    { 
  5.        return selectedItem; 
  6.    }   
  7.    set   
  8.    { 
  9.        selectedItem = value;
  10.        DoSomeActionWithSelectedItem(selectedItem);   
  11.    } 
  12. } 
  13. private Student selectedItem;
  15. private void DoSomeActionWithSelectedItem(Student student) 
  16. { 	
  17. ..... 
  18. }

In function 'DoSomeActionWithSelectedItem' you can add to list etc.

huangapple
  • 本文由 发表于 2023年2月8日 20:39:21
  • 转载请务必保留本文链接：https://go.coder-hub.com/75385916.html
  • c#
  • xamarin
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