属性更改启动长时间运行任务以填充另一个属性

Question

好的，我试着教自己MVVM模式和WPF，我遇到了一个块。

我有一个ViewModel，它有一个"SelectedProduct“字段。当设置该SelectedProduct字段时，我希望通过调用一个长时间运行的函数来填充另一个属性"BindedLimits“的内容(根据所选产品的不同，大约需要2-10秒)。理想情况下，我希望在后台启动更新，并在发生这种情况时以某种方式显示一个“进度”窗口，但我似乎找不到任何可靠的资源来说明我将如何完成这一任务，或者如果这是这样做的“正确”方式的话。

到目前为止我的ViewModel ..。

public class LimitsViewModel : PropertyChangedBase
{

    private ProductFamily selectedProduct;

    public ProductFamily SelectedProduct
    {
        get { return this.selectedProduct; }
        set
        {
            bool runLongOperation = true;

            if (value == this.selectedProduct)
            {
                runLongOperation = false;
            }

            this.SetPropertyChanged(ref this.selectedProduct, value);

            if (runLongOperation)
            {
                this.Limits = LoadLimits();
            }
        }
    }

    private ObservableCollection<BindedLimit> limits;

    public ObservableCollection<BindedLimit> Limits
    {
        get { return this.limits; }
        set
        {
            this.SetPropertyChanged(ref this.limits, value);
        }
    }

    private BindedLimit selectedLimit;

    public BindedLimit SelectedLimit
    {
        get { return this.selectedLimit; }
        set
        {
            this.SetPropertyChanged(ref this.selectedLimit, value);
        }
    }

    private ObservableCollection<BindedLimit> LoadLimits()
    {
        // Long running stuff here
    }
}

Answer 1

有点像

private ProductFamily _selectedProduct;
public ProductFamily SelectedProduct
{
    get { return _selectedProduct; }
    set
    {
        this.SetPropertyChanged(ref _selectedProduct, value)
        Limits.Clear(); // or Limits = new ...
        Task.Run(() => LongTask());
    }
}

private void LongTask()
{
    var list = new List<BindedLimit>();
    ...
    App.Current.Dispatcher.Invoke(() => Limits = new ObservableCollection<BindedItems>(list));
}

Answer 2

Sinatr与What's the best way to update an ObservableCollection from another thread?的链接帮助我找到了解决方案。这是我设计的。谢谢!

public class LimitsViewModel : PropertyChangedBase
{
    private CancellationTokenSource tokenSource;

    public LimitsViewModel()
    {
        this.tokenSource = new CancellationTokenSource();
    }

    public ICommand LoadCommand
    {
        get { return new RelayCommand(async x => await this.LoadLimits(this.tokenSource.Token)); }
    }

    private ProductFamily selectedProduct;
    public ProductFamily SelectedProduct
    {
        get { return this.selectedProduct; }
        set
        {
            this.SetPropertyChanged(ref this.selectedProduct, value);
            this.LoadCommand.Execute(null);
        }
    }

    private ObservableCollection<BindedLimit> limits;
    public ObservableCollection<BindedLimit> Limits
    {
        get { return this.limits; }
        set { this.SetPropertyChanged(ref this.limits, value); }
    }

    private bool limitsLoading;
    public bool LimitsLoading
    {
        get { return this.limitsLoading; }
        set { this.SetPropertyChanged(ref this.limitsLoading, value); }
    }

    private BindedLimit selectedLimit;
    public BindedLimit SelectedLimit
    {
        get { return this.selectedLimit; }
        set { this.SetPropertyChanged(ref this.selectedLimit, value); }
    }

    private async Task LoadLimits(CancellationToken ct)
    {
    }
}