如何僅爲可見元素引發OnPropertyChanged？

Question

我有非常大的網格。我想使用複選框「檢查/取消全選」，這將檢查/取消選中所有行。但它很慢，因爲有很多OnPtopertyChanged事件的調用。我如何才能引發OnPropertyChanged事件只爲可見元素？行的虛擬化已啓用。

Answer 1

第一種方法：取出OnPropertyChanged的認識和添加dataGrid.Items.Refresh（）;

第二種方法：在後臺更改屬性，然後

var rows = grid.FindChildren<DataGridRowsPresenter>().First() as DependencyObject; 
int count = VisualTreeHelper.GetChildrenCount(rows); 
for (int i = 0; i < count; i++) 
{ 
    DataGridRow row = VisualTreeHelper.GetChild(rows, i) as DataGridRow; 
    (row.DataContext as IViewModel).Refresh();//Refresh invokes OnPropertyChanged 
} 

Answer 2

處理此問題的一種方法是在ViewModel中具有boolean IsVisible屬性。如果IsVisible只返回true，那麼您可以提高PropertyChanged事件。

Answer 3

20000行很多:)

如果斷開的ItemsSource綁定改變你的列表視圖模型的和的ItemsSource設置爲新的檢查清單會發生什麼？如果他們想20000rows他們可以等待它

oterwise;）

編輯

如果你不改變你的ItemsSource你必須提高的PropertyChanged對每一個項目，否則你沒有看到的變化。

另一種方式是設置綁定爲空或新的列表

this.MyGridItemsViewModelProperty = new List();//"disconnect" the binding to the grid for the all check/uncheck 

然後改變你與選中/清除實時列表，並把它設回爲網格的ItemsSource

this.MyGridItemsViewModelProperty = myupdatelist; 

電網

<Grid ItemsSource="{Binding MyGridItemsViewModelProperty}" /> 

但我不知道如果第二種方法更快，你應該測試它。

Answer 4

更新1我創建了一個具有100K行的簡單repro，並在我的低規格PC上飛行，您可以檢查一下它並確認它是否足夠快？項目名稱GroupSelect然後只是複製/過去的東西到主窗口。

代碼：

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Windows; 
using System.Windows.Controls; 
using System.Windows.Data; 
using System.Windows.Documents; 
using System.Windows.Input; 
using System.Windows.Media; 
using System.Windows.Media.Imaging; 
using System.Windows.Navigation; 
using System.Windows.Shapes; 
using System.ComponentModel; 
using System.Collections.ObjectModel; 
using System.Collections.Specialized; 

namespace GroupSelect 
{ 
    /// <summary> 
    /// Interaction logic for MainWindow.xaml 
    /// </summary> 
    public partial class MainWindow : Window 
    { 
     public MainWindow() 
     { 
      InitializeComponent(); 

      this.Loaded += 
       (o, e) => 
       { 
        this.DataContext = 
         new Model(100000); 
       }; 
     } 
    } 

    public class Model : INotifyPropertyChanged 
    { 
     private bool? isAllSelected = null; 

     public Model(int itemCount) 
     { 
      this.Items = 
       Enumerable.Range(1, itemCount).Select(t => 
        new Item(this) 
       { 
        Name = "n_" + t.ToString() 
       }).ToList(); 

      this.IsAllSelected = false; 
     } 

     public List<Item> Items 
     { 
      get; 
      private set; 
     } 

     public bool? IsAllSelected 
     { 
      get 
      { 
       return this.isAllSelected; 
      } 
      set 
      { 
       if (this.IsAllSelected != value) 
       { 
        this.IsBatchUpdate = true; // updating 

        this.isAllSelected = value; 

        if (this.PropertyChanged != null) 
        { 
         this.PropertyChanged(this, 
          new PropertyChangedEventArgs("IsAllSelected")); 
        } 

        // 
        if (this.IsAllSelected.HasValue) 
        { 
         foreach (Item i in this.Items) 
         { 
          i.IsSelected = value.Value; 
         } 
        } 

        this.IsBatchUpdate = false; // updating 
       } 
      } 
     } 

     public bool IsBatchUpdate 
     { 
      get; 
      private set; 
     } 

     public event PropertyChangedEventHandler PropertyChanged; 
    } 

    public class Item: INotifyPropertyChanged 
    { 
     private bool isSelected = false; 

     public Item(Model model) 
     { 
      this.Model = model; 
     } 

     public Model Model 
     { 
      get; 
      private set; 
     } 

     public string Name 
     { 
      get; 
      set; 
     } 

     public bool IsSelected 
     { 
      get 
      { 
       return this.isSelected; 
      } 
      set 
      { 
       if (this.IsSelected != value) 
       { 
        this.isSelected = value; 

        if (this.PropertyChanged != null) 
        { 
         this.PropertyChanged(this, 
          new PropertyChangedEventArgs("IsSelected")); 
        } 

        if (!this.Model.IsBatchUpdate) 
        { 
         this.Model.IsAllSelected = null; 
        } 
       } 
      } 
     } 

     public event PropertyChangedEventHandler PropertyChanged; 
    } 
} 

標記：

<Window x:Class="GroupSelect.MainWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     xmlns:local="clr-namespace:GroupSelect" 
     Title="MainWindow" Height="350" Width="525"> 
    <Grid> 
     <DataGrid x:Name="g" AutoGenerateColumns="False" 
        ItemsSource="{Binding Path='Items'}"> 
      <DataGrid.Columns> 
       <DataGridCheckBoxColumn Binding="{Binding IsSelected, UpdateSourceTrigger=PropertyChanged}"> 
        <DataGridCheckBoxColumn.HeaderTemplate> 
         <DataTemplate> 
          <CheckBox HorizontalAlignment="Center" 
             DataContext="{Binding Path=DataContext, 
             RelativeSource={RelativeSource AncestorType={x:Type Window}}}" 
             IsChecked="{Binding Path=IsAllSelected, UpdateSourceTrigger=PropertyChanged}"/> 
         </DataTemplate> 
        </DataGridCheckBoxColumn.HeaderTemplate> 
       </DataGridCheckBoxColumn> 
       <DataGridTextColumn Header="Name" Binding="{Binding Name}"/> 
      </DataGrid.Columns> 
     </DataGrid> 
    </Grid> 
</Window>