wpf - WPF PRISM : IRegionMemberLifetime KeepAlive doesn't get called

我需要根据特定条件切换显示的 View 。
我已经在 ViewModel 的构造函数中实现了切换逻辑

我在 View 上实现IRegionMemberLifetime并将KeepAlive设置为false，以便始终获得View和ViewModel的新实例。

但是由于某些原因，当我单击导航按钮时，我在KeepAlive处的断点永远不会到达，并且我得到的是 MainView 而不是 WelcomeView 。

这是供您引用的代码:

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}"/>

查看模型:

[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 View 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; }
}

最佳答案

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

IRegionMemberLifetime接口(interface)和RegionMemberLifetimeAttribute都可以完成相同的操作，并且可以在您的View或ViewModel上定义(前提是将ViewModel设置为DataContext)。

这是相关的代码:

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;
    }

我什至可以步进这些代码来查看它如何与我的应用程序交互。要回答您的问题，如果您的KeepAlive属性没有被击中，那么它不会从ActiveView中删除。还要确保，如果要通过IoC从容器解析 View ，则尚未将其注册为单例类型(每次解析时都会得到一个新实例)。属性/接口(interface)只会将其完全从区域中删除，不能保证您会获得一个新的实例。

关于wpf - WPF PRISM : IRegionMemberLifetime KeepAlive doesn't get called，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/12774539/