我认为我的设置相当标准,使用了一个由
我需要对
奇怪的是,在开始
我已经制定了一个完整的工作示例。
XAML:
ObservableCollection
支持的ListBox
。我需要对
ObservableCollection
中的Thing
执行一些工作,这可能需要很长时间(超过几百毫秒),因此我想将其转移到Task
上(我也可以在此处使用BackgroundWorker
)以避免冻结UI。奇怪的是,在开始
Task
之前进行CollectionViewSource.GetDefaultView(vm.Things).CurrentItem
一切正常,但如果在Task
期间发生这种情况,则CurrentItem
似乎总是指向ObservableCollection
中的第一个元素。我已经制定了一个完整的工作示例。
XAML:
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<DockPanel>
<ToolBar DockPanel.Dock="Top">
<Button Content="Click Me Sync" Click="ButtonSync_Click" />
<Button Content="Click Me Async Good" Click="ButtonAsyncGood_Click" />
<Button Content="Click Me Async Bad" Click="ButtonAsyncBad_Click" />
</ToolBar>
<TextBlock DockPanel.Dock="Bottom" Text="{Binding Path=SelectedThing.Name}" />
<ListBox Name="listBox1" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding Path=Things}" SelectedItem="{Binding Path=SelectedThing}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Name}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</DockPanel>
</Window>
C#:
public partial class MainWindow : Window
{
private readonly ViewModel vm;
public MainWindow()
{
InitializeComponent();
vm = new ViewModel();
DataContext = vm;
}
private ICollectionView GetCollectionView()
{
return CollectionViewSource.GetDefaultView(vm.Things);
}
private Thing GetSelected()
{
var view = GetCollectionView();
return view == null ? null : (Thing)view.CurrentItem;
}
private void NewTask(Action start, Action finish)
{
Task.Factory
.StartNew(start)
.ContinueWith(t => finish());
//.ContinueWith(t => finish(), TaskScheduler.Current);
//.ContinueWith(t => finish(), TaskScheduler.Default);
//.ContinueWith(t => finish(), TaskScheduler.FromCurrentSynchronizationContext());
}
private void ButtonSync_Click(object sender, RoutedEventArgs e)
{
var thing = GetSelected();
DoWork(thing);
MessageBox.Show("all done");
}
private void ButtonAsyncGood_Click(object sender, RoutedEventArgs e)
{
var thing = GetSelected(); // outside new task
NewTask(() =>
{
DoWork(thing);
}, () =>
{
MessageBox.Show("all done");
});
}
private void ButtonAsyncBad_Click(object sender, RoutedEventArgs e)
{
NewTask(() =>
{
var thing = GetSelected(); // inside new task
DoWork(thing); // thing will ALWAYS be the first element -- why?
}, () =>
{
MessageBox.Show("all done");
});
}
private void DoWork(Thing thing)
{
Thread.Sleep(1000);
var msg = thing == null ? "nothing selected" : thing.Name;
MessageBox.Show(msg);
}
}
public class ViewModel
{
public ObservableCollection<Thing> Things { get; set; }
public Thing SelectedThing { get; set; }
public ViewModel()
{
Things = new ObservableCollection<Thing>();
Things.Add(new Thing() { Name = "one" });
Things.Add(new Thing() { Name = "two" });
Things.Add(new Thing() { Name = "three" });
Things.Add(new Thing() { Name = "four" });
}
}
public class Thing
{
public string Name { get; set; }
}
CollectionViewSource.GetDefaultView(vm.Things)
是否存在,然后再在任务内部使用ReferenceEquals
检查CollectionViewSource.GetDefaultView(vm.Things)
。 - Daniel Hilgarth