将变量从 ViewModel 传递到另一个 View (MVVMCross) [英] Passing on variables from ViewModel to another View (MVVMCross)

问题描述

在过去的几周里，我一直致力于使用 MVMCross 框架开发跨平台应用程序 (IOS/Android/WP7).今天我遇到了一个我真的不知道如何解决的问题，所以希望你能把我推向正确的方向.

For the past couple of weeks I've been working on developing a cross platform app (IOS/Android/WP7) using the MVVMCross framework. Today I ran into a problem I don't really know how to solve, so hopefully you can push me in the right direction.

在 IOS 中，我使用以下结构导航到另一个页面(以下代码位于 ViewModel 中):

In the IOS I have the following construction for navigating to another page (the code below is located in a ViewModel):

KeyValuePair<string,string> kvpAct1 = new KeyValuePair<string, string>("short", ".countertest5");

public IMvxCommand BeckhoffActuator1
{
    get
    {           
        return new MvxRelayCommand<Type>((type) => this.RequestNavigate<Beckhoff.BeckhoffActuatorViewModel>(kvpAct1));
    }
}

当这个 IMvxCommand 被触发(按下按钮)时，下一个视图被加载，在这种情况下是 BeckhoffActuatorViewModel.在 BeckhoffActuatorView 的代码中，我使用了上面的键值对:

When this IMvxCommand is fired (button pressed) the next View is loaded, in this case the BeckhoffActuatorViewModel. In the code of the BeckhoffActuatorView I use the keyvaluepair from above:

public class BeckhoffActuatorView : MvxTouchDialogViewController<BeckhoffActuatorViewModel>
{

    ICollection<string> icol;

    public BeckhoffActuatorView(MvxShowViewModelRequest request) : base(request, UITableViewStyle.Grouped, null, true)
    {

        icol = request.ParameterValues.Values;

    }

    public override void ViewDidLoad()
    {
        //Code
    }
}

此结构在 IOS 中运行良好，但我想在我的 android 应用程序中使用相同的结构.

This construction is working fine in IOS, but I would like to use the same construction in my android App.

ViewModel 中的代码没有改变，因为那是 MVVM 的全部思想.但是 Android 的 BackhoffActuatorView 的代码是不同的:

The code in the ViewModel hasn't changed since that's the whole idea of MVVM. But the code of the BackhoffActuatorView is different for Android:

public class BeckhoffActuatorView : MvxBindingActivityView<BeckhoffSensorViewModel>
{
    public ICollection<string> icol;

    public BeckhoffActuatorView()
    {
        Debug.WriteLine("Standard");
    }

    public BeckhoffActuatorView(MvxShowViewModelRequest request)
    {
        Debug.WriteLine("Custom");

        icol = request.ParameterValues.Values;
    }

    protected override void OnViewModelSet()
    {

        SetContentView(Resource.Layout.BeckhoffActuatorView);

    }
}

上面的代码不起作用，MvxBindingActivityView 似乎没有实现类似于我在 IOS 中使用的 ViewController 的东西.代码只出现在标准构造函数中，当我完全忽略它时，它不会编译/运行.

The code above isn't working, the MvxBindingActivityView doesn't seem to implement something similar to the ViewController I use in IOS. The code only come in the standard constructor, and when I leave that one out completely it won't compile/run.

有谁知道我可以访问我通过 RequestNavigate 发送的键值对?谢谢！

Does anyone know know I can access the keyvaluepair I send with the RequestNavigate? Thank you!

推荐答案

MVVMCross 非常基于约定 - 它的工作原理是尽可能在 ViewModel 之间传递消息.

MVVMCross is very convention based - and it works on the idea of passing messages between ViewModels wherever possible.

如果您使用以下方法导航到 ViewModel:

If you navigate to a ViewModel using:

KeyValuePair<string,string> kvpAct1 = new KeyValuePair<string, string>("short", ".countertest5");

public IMvxCommand BeckhoffActuator1
{
    get
    {           
        return new MvxRelayCommand<Type>((type) => this.RequestNavigate<Beckhoff.BeckhoffActuatorViewModel>(kvpAct1));
    }
}

那么您应该能够使用构造函数在 BeckhoffActuatorViewModel 中获取它:

then you should be able to pick that up in the BeckhoffActuatorViewModel using the constructor:

public class BeckhoffActuatorViewModel : MvxViewModel
{
    public BeckhoffActuatorViewModel(string short)
    {
        ShortValue = short;
    }

    private string _shortValue;
    public string ShortValue
    {
        get
        {
            return _shortValue;
        }
        set
        {
            _shortValue = value;
            FirePropertyChanged("ShortValue");
        }
    }
}

然后你的视图可以访问 ViewModel.ShortValue(对于 iOS，这可以在 base.ViewDidLoad() 之后完成，对于 OnCreate() 之后的 Android 和 OnNavigatedTo 之后的 WP7)

And your views can then access ViewModel.ShortValue (for iOS this can be done after base.ViewDidLoad(), for Android after OnCreate() and for WP7 after OnNavigatedTo)

有关此示例，请查看 TwitterSearch 示例:

For an example of this, take a look at the TwitterSearch example:

• https://github.com/slodge/MvvmCrossTwitterSearch

这有一个 HomeViewModel 调用导航使用:

This has a HomeViewModel which calls navigate using:

    private void DoSearch()
    {
        RequestNavigate<TwitterViewModel>(new { searchTerm = SearchText });
    }

和一个使用构造函数接收 searchTerm 的 TwitterViewModel:

and a TwitterViewModel which receives the searchTerm using the constructor:

    public TwitterViewModel(string searchTerm)
    {
        StartSearch(searchTerm);
    }

请注意，目前仅允许在此消息传递中使用 string - 但您始终可以使用 JSON.Net 序列化您自己的对象 - 或者您可以扩展框架 - 它是开放的来源.

Please note that only strings are allowed in this message passing at present - but you can always serialise your own objects using JSON.Net - or you can extend the framework - it's open source.

请注意，这里只允许 strings、ints、doubles 和 bools当前传递的构造函数参数 - 这是由于 Xaml Urls 和 Android Intent 的序列化要求.如果您想使用自己的自定义序列化对象尝试导航，请参阅 http://slodge.blogspot.co.uk/2013/01/navigating-between-viewmodels-by-more.html.

Please note that only strings, ints, doubles and bools are allowed in this constructor parameter passing at present - this is due to serialisation requirements for Xaml Urls and for Android Intents. If you want to experiment with navigation using your own custom serialised objects, then please see http://slodge.blogspot.co.uk/2013/01/navigating-between-viewmodels-by-more.html.

另外，请注意，如果您想使用匿名对象导航 (RequestNavigate(new { searchTerm = SearchText });)，那么您需要确保 InternalsVisibleTo 属性已设置 - 参见 https://github.com/slodge/MvvmCrossTwitterSearch/blob/master/TwitterSearch.Core/Properties/AssemblyInfo.cs:

Also, note that if you want to use the anonymous object navigation (RequestNavigate<TwitterViewModel>(new { searchTerm = SearchText });) then you will need to make sure that an InternalsVisibleTo attribute is set - see https://github.com/slodge/MvvmCrossTwitterSearch/blob/master/TwitterSearch.Core/Properties/AssemblyInfo.cs:

[assembly: InternalsVisibleTo("Cirrious.MvvmCross")]

<小时>

此外……不适合胆小的人……这不是好的 mvvm 代码"……但是如果您真的想要/需要访问 Android 活动中的 MvxShowViewModelRequest 数据，那么您可以提取它来自传入的 Intent - 有一个包含请求的 Extras 字符串(请参阅 https://github.com/slodge/MvvmCross/blob/master/Cirrious/Cirrious.MvvmCross/Android/Views/MvxAndroidViewsContainer.cs)

---

Further... not for the faint-hearted... and this isn't "good mvvm code"... but if you really want/need to access the MvxShowViewModelRequest data inside an Android activity, then you can extract it from the incoming Intent - there's an Extras string containing the request (see the deserialisation in CreateViewModelFromIntent in https://github.com/slodge/MvvmCross/blob/master/Cirrious/Cirrious.MvvmCross/Android/Views/MvxAndroidViewsContainer.cs)

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