代码之家 › 专栏 › 技术社区 › Willy

MVVM:在WPF NET 3.5中完成线程池工作项后更新视图的控件可见性

threadpool mvvm multithreading wpf c#

Willy · 技术社区 · 8 年前

此启动绑定到视图模型中的属性“IsSplashVisible”,因此将属性更新为true,通知启动在开始时显示,并将其设置为false,通知启动隐藏。

低于代码。

public class TestViewModel : BaseViewModel
{
    private static Dispatcher _dispatcher;
    public ObservableCollection<UserData> lstUsers

    public ObservableCollection<UserData> LstUsers
    {
        get
        {
            return this.lstUsers;
        }

        private set
        {
            this.lstUsers= value;
            OnPropertyChanged("LstUsers");
        }
    }

    private bool isSplashVisible = false;

    public bool IsSplashVisible 
    {
            get
            {
                return this.isSplashVisible;
            }

            set
            {
                if (this.isSplashVisible== value)
                {
                    return;
                }

                this.isSplashVisible= value;
                OnPropertyChanged("IsSplashVisible");
            }
    }

    public TestViewModel()
    {
        this.IsSplashVisible = true;

        ThreadPool.QueueUserWorkItem(new WaitCallback((o) =>
        {
            var result = getDataFromDatabase();
            UIThread(() => 
            {
               LstUsers = result;
               this.IsSplashVisible = false; <---- HERE IT FAILS
            });            
        }));
    }

    ObservableCollection<UserData> getDataFromDatabase()
    {            
        return this.RequestDataToDatabase();
    }

    static void UIThread(Action a)
    {
        if(_dispatcher == null) _dispatcher = Dispatcher.CurrentDispatcher;
        //this is to make sure that the event is raised on the correct Thread
        _dispatcher.Invoke(a); <---- HERE EXCEPTION IS THROWN
    }
}

1 回复 | 直到 8 年前

Clemens 8 年前

Dispatcher.CurrentDispatcher

获取当前执行的线程的调度程序,如果尚未与该线程关联,则创建新的调度程序。

您应该使用当前应用程序实例的调度程序:

ThreadPool.QueueUserWorkItem(o =>
{
    var result = getDataFromDatabase();

    Application.Current.Dispatcher.Invoke(() => 
    {
        LstUsers = result;
        IsSplashVisible = false;
    });            
});

Dispatcher.CurrentDispatcher 在UI线程中而不是在线程池线程中调用。然而,该字段是完全冗余的。你可以随时打电话 Application.Current.Dispatcher.Invoke()

public class TestViewModel
{
    private readonly Dispatcher _dispatcher = Dispatcher.CurrentDispatcher;

    public TestViewModel()
    {
        IsSplashVisible = true;

        ThreadPool.QueueUserWorkItem(o =>
        {
            var result = getDataFromDatabase();

            _dispatcher.Invoke(() => 
            {
               LstUsers = result;
               IsSplashVisible = false;
            });            
        });
    }

    ...
}