问题介绍
当ObservableCollection列表被UI线程占用时，如果在异步线程中调用ObservableCollection，会弹出以下异常：
问题分析
我们使用一个viewModel，在ViewModel中添加ObservableCollection类型的ItemsSource列表。
在列表使用ListBox绑定ItemsSource列表。再由界面触发对ItemsSource的修改。
1 public class ViewModel : INotifyPropertyChanged
2 {
3 private ObservableCollection<string> _itemsSource = new ObservableCollection<string>();
4
5 public ObservableCollection<string> ItemsSource
6 {
7 get => _itemsSource;
8 set
9 {
10 _itemsSource = value;
11 OnPropertyChanged();
12 }
13 }
14
15 public event PropertyChangedEventHandler PropertyChanged;
16
17 [NotifyPropertyChangedInvocator]
18 protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
19 {
20 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
21 }
22
View Code
1. 直接在异步线程下修改ObservableCollection--报错
1 private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
2 {
3 var viewModel = this.DataContext as ViewModel;
4 Task.Run(() =>
5 {
6 //此段调用异常
7 viewModel.ItemsSource.Add("test1");
8 });
9
2. 在异步线程下，赋值ObservableCollection--正常
1 private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
2 {
3 var viewModel = this.DataContext as ViewModel;
4 Task.Run(() =>
5 {
6 //此段不会报错
7 var list = viewModel.ItemsSource.ToList();
8 list.Add("test0");
9 viewModel.ItemsSource = new ObservableCollection<string>(list);
10 });
11
3. 在异步线程下，赋值ObservableCollection后，再修改ObservableCollection--正常
1 private void Button1_OnClick(object sender, RoutedEventArgs e)
2 {
3 var viewModel = this.DataContext as ViewModel;
4 Task.Run(() =>
5 {
6 //此段不会报错
7 viewModel.ItemsSource = new ObservableCollection<string>(new List<string>() { "test3", "test2" });
8 //此段不会报错
9 viewModel.ItemsSource.Add("test4");
10 });
11
在异步线程下设置的ItemsSource，可以被当前异步线程调用。
4. 异步线程下赋值ObservableCollection，然后在UI线程修改ObservableCollection--正常
1 private void Button1_OnClick(object sender, RoutedEventArgs e)
2 {
3 var viewModel = this.DataContext as ViewModel;
4 Task.Run(() =>
5 {
6 //此段不会报错
7 viewModel.ItemsSource = new ObservableCollection<string>(new List<string>() { "test0" });
8 });
9 }
10
11
12 private void Button2_OnClick(object sender, RoutedEventArgs e)
13 {
14 var viewModel = this.DataContext as ViewModel;
15 //此段不会报错
16 viewModel.ItemsSource.Add("test2");
17
在异步线程下设置的ItemsSource，可以被UI线程调用。此处可以理解为，赋值时，框架默默转到UI线程处理了？
但是上面3流程，为何正常，so weird~
5. 异步线程下，回到UI线程中，修改ObservableCollection--正常
1 private void Button1_OnClick(object sender, RoutedEventArgs e)
2 {
3 var viewModel = this.DataContext as ViewModel;
4 Task.Run(() =>
5 {
6 Application.Current.Dispatcher.Invoke(() =>
7 {
8 //此段不会报错
9 viewModel.ItemsSource.Add("test");
10 });
11 });
12
作者：唐宋元明清2188