mvvm - 使用异步访问 UI 线程 / 使用 Mvvm 等待

Question

我想使用 Mvvm 模式在带有进度指示器的 DocumentViewer 上传递一些内容，这一代将在从 db 异步获取数据后使用 UiElements。

    public async void ProcessReportAsync(){

        IsBusy = true;

        _reportDal = new ReportDal(_sprocName,_sprocParams);
        ReportContainers = new ObservableCollection<ReportContainerViewModel>();

        await Task.Run(() => _reportDal.InitReportDal());
        ReportDataTable = _reportDal.DataTableReport;

        await  Task.Run(() => ProcessedElements());

        var t3 = Task.Run(() => ProcessPage(_reportPage));
        var t4 = Task.Run(() => ProcessContainerData());
        await Task.WhenAll(t3, t4);
        var p = new PrinterViewModel(this);

      // This statement does'nt complete its execuation, which is adding more UIElements
        if(DispatcherHelper.UIDispatcher.CheckAccess()) {

            DispatcherHelper.UIDispatcher.Invoke(
                ()=>_document = p.CreateDocument(new Size(p.PrintDialog.PrintableAreaWidth,p.PrintDialog.PrintableAreaHeight))
                ,DispatcherPriority.Background);

        }
     // Can't reach this code
        IsBusy = false;


    }

Answer 1

async/的一个很好的方面await是它负责为您分派回正确的上下文。

public async Task ProcessReportAsync()
{
    IsBusy = true;

    _reportDal = new ReportDal(_sprocName,_sprocParams);
    ReportContainers = new ObservableCollection<ReportContainerViewModel>();

    await Task.Run(() => _reportDal.InitReportDal());
    ReportDataTable = _reportDal.DataTableReport;

    await Task.Run(() => ProcessedElements());

    var t3 = Task.Run(() => ProcessPage(_reportPage));
    var t4 = Task.Run(() => ProcessContainerData());
    await Task.WhenAll(t3, t4);
    var p = new PrinterViewModel(this);

    _document = p.CreateDocument(new Size(p.PrintDialog.PrintableAreaWidth,p.PrintDialog.PrintableAreaHeight));

    IsBusy = false;
}

我建议您阅读我的async/ awaitintro和我的MSDN 文章async。