Question

好的，所以我试图自学MVVM模式和WPF，并且我遇到了阻塞。

我有一个ViewModel，它有一个＆＃34; SelectedProduct＆＃34;领域。当设置了SelectedProduct字段时，我想通过调用一个长时间运行的函数来填充另一个属性＆＃34; BindedLimits＆＃34;的内容（根据选择的产品大约需要2-10秒）。理想情况下，我想在后台启动更新，并以某种方式显示＆＃34;进展＆＃34;这个窗口正在发生，但我似乎找不到任何有关如何实现这一目标的可靠资源，或者如果这甚至是＆＃34;正确的＆＃34;做这样的事情的方式。

到目前为止，这是我的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

像

这样的东西

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。这就是我设计的。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)
    {
    }
}

在物业变更启动长期运行任务以填充另一个物业

2 个答案: