Question

我尝试在导航到附加到该视图模型的页面之前，将值传递给另一个视图模型中的视图模型。我以前将它传递给视图，然后将其传递给视图模型。这似乎是一种笨拙的做事方式。我没有使用任何类型的框架，所以这不是一个选项。目前该属性设置为静态，这有效但我不确定这是否是一个好习惯。代码：

查看模型1：

此命令将打开新页面：

public void OpenRouteDetails()
{
   RouteStopPopOverViewModel.RouteName = "TestRoute";
   App.Page.Navigation.PushAsync(new RouteStopPopOverView());            
}

查看模型2：（RouteStopPopOverViewModel）

public static string RouteName { get; set; }

这确实有效，但我不想使用静态作为实现此目的的方法。有没有办法设置RouteName属性而不使用静态或通过view-＆gt;传递它查看模型。我已经看到了一些关于这方面的答案，但他们似乎没有清楚地回答问题。

Answer 1

这里是您可以通过导航轻松实现您的要求的示例

public class ViewModelFrom : BaseViewModel
{
    async Task ExecuteCommand()
     {
        string routeName="value to trasfer";
        Navigation.PushAsync(new View(routeName));
     }
}


public partial class View : ContentPage
{
    public View(string routeName)
    {
        InitializeComponent();
        BindingContext = new ViewModelTo(routeName);
     }
}

public class ViewModelTo : BaseViewModel
{
    public string RouteName { get; set; }

    public ViewModelTo(string routeName)
    {
         RouteName=routeName;
    }
}

Answer 2

在视图模型之间共享控制器类必须在两个视图模型中为构造函数提供相同的实例因此，您可以设置值，并在两个视图模型中监听事件控制器类成为中介。

public class SharedController : IControlSomething
{
    private string _sharedValue;

    public string SharedValue
    {
        get => _sharedValue;
        set
        {
            if (_sharedValue == value)
                return;

            _sharedValue = value;
            OnSharedValueUpdated();
        }
    }

    public event EventHandler SharedValueUpdated;

    protected virtual void OnSharedValueUpdated()
    {
        SharedValueUpdated?.Invoke(this, EventArgs.Empty);
    }
}

public class ViewModel1
{
    private readonly IControlSomething _controller;

    public ViewModel1(IControlSomething controller)
    {
        // Save to access controller values in commands
        _controller = controller;
        _controller.SharedValueUpdated += (sender, args) =>
        {
            // Handle value update event
        };
    }
}

public class ViewModel2
{
    private readonly IControlSomething _controller;

    public ViewModel2(IControlSomething controller)
    {
        // Save to access controller values in commands
        _controller = controller;
        _controller.SharedValueUpdated += (sender, args) =>
        {
            // Handle value update event
        };
    }
}

Answer 3

如果存在层次结构，则可以在父级中表达这两种层次结构。

public class Route
{
    private string Name;
}

public class RouteSelectedArgs : EventArgs
{
    public Route Selected { get; set; }
}

public interface IRouteSelection
{
    event EventHandler<RouteSelectedArgs> RouteSelected;
}

public interface IRouteDetails { }

public class RouteWizard
{
    public UserControl view { get; set; }

    private IRouteSelection _selection;
    private IRouteDetails _details;

    public RouteWizard(IRouteSelection selection, IRouteDetails details)
    {
        _selection = selection;
        _details = details;
        _selection.RouteSelected += Selection_RouteSelected;
        view = MakeView(_selection);
    }

    private void Selection_RouteSelected(object sender, RouteSelectedArgs e)
    {
        _selection.RouteSelected -= Selection_RouteSelected;
        view = MakeView(_details, e.Selected);

    }

    private UserControl MakeView(params object[] args)
    {
        ////magic
        throw new NotImplementedException();
    }
}

Answer 4

当您使用MVVM模式时，您可以使用众多MVVM框架中的一个来实现此目的。

我使用FreshMvvm，它允许我在视图模型之间传递参数，如

await CoreMethods.PushPageModel<SecondPageModel>(myParameter, false);

然后在SecondPageModel中，我可以看到访问Init方法中的参数

private MyParamType _myParameter;

public override void Init(object initData)
{
    base.Init(initData);

    var param = initData as MyParamType;
    if (param != null)
    {
        _myParameter = param;
    }
}

You can find more details about FreshMvvm here虽然大多数MVVM框架都具有类似的功能。

在另一个ViewModel的ViewModel中设置一个Property

4 个答案: