[英]refresh bindings in itemscontrol wpf
我有一个简单的项控件绑定到条目对象列表。 该按钮更新列表中每个项目的LastUpdated。 如何引发属性更改事件,以便在ItemsControl中更新LastUpdated字段。 我简化了我的示例,只是为了弄清绑定问题。 我的真实样本使用PRISM和第三方控件。
C#代码:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Input;
namespace TestItemsControl
{
public class Entry
{
public string Name { get; set; }
public DateTime LastUpdated { get; set; }
}
}
namespace TestItemsControl
{
public class TestViewModel: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public List<Entry> Entries { get; set; }
public ICommand UpdateCmd { get; set; }
public TestViewModel()
{
this.Entries = new List<Entry>();
this.Entries.Add(new Entry{ Name = "1", LastUpdated = DateTime.Now });
this.Entries.Add(new Entry { Name = "2", LastUpdated = DateTime.Now });
this.Entries.Add(new Entry { Name = "3", LastUpdated = DateTime.Now });
}
public void Refresh()
{
if (this.PropertyChanged!= null)
{
PropertyChanged(this, new PropertyChangedEventArgs("Entries"));
}
}
}
}
XAML:
<Application x:Class="TestItemsControl.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestItemsControl"
StartupUri="MainWindow.xaml">
<Application.Resources>
<local:TestViewModel x:Key="viewModel"/>
</Application.Resources>
</Application>
<Window x:Class="TestItemsControl.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:TestItemsControl"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525" DataContext="{StaticResource viewModel}">
<Grid>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<ItemsControl Grid.Row="0" ItemsSource="{Binding Entries}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding Name}"/>
<TextBlock Text="{Binding LastUpdated}"/>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<Button Grid.Row="1" Content="Update" Click="Button_Click"/>
</Grid>
</Window>
然后,您必须重写Entry
类
public class Entry: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public string Name { get; set; }
DateTime lastUD;
public DateTime LastUpdated
{
get
{
return lastUD;
}
set
{
lastUD = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("LastUpdated"));
}
}
}
另外,将List<Entry>
更改为ObservableCollection<Entry>
:
namespace TestItemsControl
{
public class TestViewModel
{
public ObservableCollection<Entry> Entries=new ObservableCollection<Entry>();
public ICommand UpdateCmd { get; set; }
public TestViewModel()
{
this.Entries.Add(new Entry{ Name = "1", LastUpdated = DateTime.Now });
this.Entries.Add(new Entry { Name = "2", LastUpdated = DateTime.Now });
this.Entries.Add(new Entry { Name = "3", LastUpdated = DateTime.Now });
}
}
}
这样,您不必调用Refesh函数。
如果没有人订阅活动,则必须检查Null
public class Entry : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public string Name { get; set; }
DateTime lastUD;
public DateTime LastUpdated
{
get
{
return lastUD;
}
set
{
lastUD = value;
if(PropertyChanged != NULL)
PropertyChanged(this, new PropertyChangedEventArgs("LastUpdated"));
}
}
}
我认为您必须在这里选择:
创建这样的方法:
protected void OnPropertyChanged(string) { var handler = PropertyChanged; if (handler != null) { handler(this, new PropertyChangedEventArgs(propertyName)); } }
然后,每当您要更新属性时,都可以:
OnPropertyChanged("TheNameOfTheProperty");
或者如果您想更新该类中的每个属性:
OnPropertyChanged(string.Empty);
如果不确定何时更新哪个属性,建议您选择后者。
您没有绑定UpdateCmd并在任何地方调用Refresh,除非它在Click处理程序中,但是您应该使用MVVM方法来执行此操作。
将Click事件处理程序更改为来自xaml中的viewmodel的命令绑定,如下所示
<Button Grid.Row="1" Content="Update" Command={Binding UpdateCmd}/>
然后在视图模型的构造函数绑定中,创建一个新的RelayCommand或ICommand实现类的样子,以便构造器接收动作委托。
this.UpdateCmd = new RelayCommand(this.Update);
另外,您可能应该将“刷新”更改为“更新”,以更新条目的时间戳。
public void Update()
{
foreach (var entry in this.Entries)
{
entry.LastUpdated = DateTime.Now;
}
if (this.PropertyChanged!= null)
{
PropertyChanged(this, new PropertyChangedEventArgs("Entries"));
}
}
但实际上,您也应该仅在Entry模型上实现INotifyPropertyChanged并在属性设置器上引发事件,绑定将被更新,而不会通知整个集合应被更新。
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