Question

我需要根据特定条件切换正在显示的视图。我已经在 ViewModel

的构造函数中实现了切换逻辑

我正在查看上实施IRegionMemberLifetime并将KeepAlive设置为false，以便我始终获得View和ViewModel的新实例。< / p>

但出于某种原因，当我点击导航按钮时，KeepAlive处的断点永远不会到达，我得到 MainView 而不是 WelcomeView

以下是供您参考的代码：

导航按钮：

<Controls:SignedButton VerticalAlignment="Top" Width="275" Height="45"
    Foreground="#FFFFFF" 
    LeftSign="&lt;" Text="Back to Accounts" 
    TextSize="20" ButtonBackground="#666666" 
    HoverBackground="#0FBDAC" HoverOpacity="1" Margin="0,25,0,0"
    Command="{x:Static Infrastructure:ApplicationCommands.NavigateCommand}"
    CommandParameter="{x:Type Views:MainView}"/>

查看型号：

[RegionMemberLifetime(KeepAlive = false)]
public class MainViewModel : ViewModel, IMainViewModel
{
    private readonly IUnityContainer _container;
    private readonly IRegionManager _regionManager;

    public MainViewModel(IUnityContainer container, IRegionManager regionManager)
    {
        _container = container;
        _regionManager = regionManager;

        Accounts = new List<Account>();

        if (Accounts.Any()) return;

        IRegion region = _regionManager.Regions[Regions.Main];

        var views = region.Views;
        foreach (var view in views)
        {
            region.Remove(view);
        }

        region.Add(_container.Resolve<IWelcomeView>());
    }

    public IList<Account> Accounts { get; private set; }
}

查看模型库：

public abstract class ViewModel : IViewModel
{
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

查看：

[RegionMemberLifetime(KeepAlive = false)]
public partial class MainView : UserControl, IMainView
{
    public MainView(IMainViewModel mainViewModel)
    {
        InitializeComponent();

        ViewModel = mainViewModel;
    }

    public IViewModel ViewModel
    {
        get { return (IViewModel) DataContext; }
        set { DataContext = value; }
    }
}

Shell视图模型：

public class ShellViewModel : ViewModel, IShellViewModel
{
    private readonly IRegionManager _regionManager;

    public ShellViewModel(IRegionManager regionManager)
    {
        _regionManager = regionManager;

        NavigateCommand = new DelegateCommand<object>(Navigate);
        ApplicationCommands.NavigateCommand.RegisterCommand(NavigateCommand);
    }

    private void Navigate(object navigatePath)
    {
        if (navigatePath != null)
        {
            _regionManager.RequestNavigate(Regions.Main, navigatePath.ToString());
        }
    }

    public DelegateCommand<object> NavigateCommand { get; private set; }
}

Answer 1

在Prism库中查看RegionMemberLifetimeBehavior类会很有用（对我来说，它位于C：\ Prism4 \ PrismLibrary \ Desktop \ Prism \ Regions \ Behaviors）

IRegionMemberLifetime接口和RegionMemberLifetimeAttribute都完成相同的事情，可以在View或ViewModel上定义（前提是viewmodel设置为DataContext）。

以下是相关的代码：

private void OnActiveViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // We only pay attention to items removed from the ActiveViews list.
        // Thus, we expect that any ICollectionView implementation would
        // always raise a remove and we don't handle any resets
        // unless we wanted to start tracking views that used to be active.
        if (e.Action != NotifyCollectionChangedAction.Remove) return;

        var inactiveViews = e.OldItems;
        foreach (var inactiveView in inactiveViews)
        {
            if (!ShouldKeepAlive(inactiveView))
            {
                this.Region.Remove(inactiveView);
            }
        }
    }

    private static bool ShouldKeepAlive(object inactiveView)
    {
        IRegionMemberLifetime lifetime = GetItemOrContextLifetime(inactiveView);
        if (lifetime != null)
        {
            return lifetime.KeepAlive;
        }

        RegionMemberLifetimeAttribute lifetimeAttribute = GetItemOrContextLifetimeAttribute(inactiveView);
        if (lifetimeAttribute != null)
        {
            return lifetimeAttribute.KeepAlive;
        }

        return true;
    }

我甚至可以使用此代码来查看它与我的应用程序的交互方式。要回答您的问题，如果您的KeepAlive属性未被命中，则不会从ActiveView中删除它。还要确保如果您通过IoC从容器中解析您的视图，您还没有将其注册为单例类型（每次解析时都会获得一个新实例）。属性/接口只会从区域中完全删除它，不能保证你得到一个新的实例。

WPF PRISM：IRegionMemberLifetime不会调用KeepAlive

1 个答案: