Xamarin.Android和Spinner与ReactiveUI绑定 [英] Xamarin.Android and Spinner binding with ReactiveUI

问题描述

我正在尝试在Xamarin.Android应用程序中使用ReactiveUI绑定到Spinner。要将项目添加到 Spinner ，我需要使用 ArrayAdapter 。但是 ArrayAdapter 需要 Android.Content.Context 。我应该将其传递给ViewModel吗？

I'm trying to bind to a Spinner using ReactiveUI in a Xamarin.Android application. To add items to the Spinner, I need to use ArrayAdapter. But ArrayAdapter needs Android.Content.Context. Should I pass it into the ViewModel?

有人知道Xamarin.Android编写的应用程序，该应用程序使用ReactiveUI，在哪里可以找到灵感？ ReactiveUI文档仅引用了为iOS编写的示例应用程序。

Anyone know about an application written in Xamarin.Android, which uses ReactiveUI, where I could look inspiration? The ReactiveUI documentation only has a reference to a sample application written for iOS.

    <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView
        android:id="@+id/Label"
        android:text="Zařízení:"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <Spinner
        android:id="@+id/Devices"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/Label"/>

    <Button
        android:id="@+id/EditCommand"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/Devices"
        android:text="Edit"/>
</RelativeLayout>

活动

Activity

namespace Test.Droid
{
    [Activity(Label = "Test.Droid", MainLauncher = true)]
    public class MainActivity : ReactiveActivity, IViewFor<MainViewModel>
    {
        public Spinner Devices { get; private set; }

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            SetContentView(Resource.Layout.Main);
            ViewModel = new MainViewModel();
            this.WireUpControls();

            // Bindings

            this.Bind(this.ViewModel, ) // ?
        }


        private MainViewModel _viewModel;
        public MainViewModel ViewModel
        { get => _viewModel; set { this.RaiseAndSetIfChanged(ref _viewModel, value); } }

        object IViewFor.ViewModel
        { get => ViewModel; set { ViewModel = (MainViewModel)value; } }
    }
}

ViewModel

ViewModel

namespace Test.Droid.ViewModels
{
    public class MainViewModel : ReactiveObject
    {
        // How to databind Spinner Devices ?


        public MainViewModel()
        {           
        }
    }
}

推荐答案

我没有做过Xamarin.Android开发，但总的来说，您不想传递有关视图的详细信息

I haven't done any Xamarin.Android development, but in general you don't want to pass details about the view into the ViewModel - it should not know anything about the view.

我会将项目列表作为集合公开（例如， IList< Item> ），并在绑定上使用转换器创建 ArrayAdapter ：

I would expose the list of items as a collection (e.g. IList<Item>) and use a converter on the binding to create an ArrayAdapter:

this.OneWayBind(this.ViewModel.Devices, this.View.Property, devices => new ArrayAdapter(devices));

this.View.Property 应该引用当设备列表更改时更改的属性。第三个参数（ devices => new ArrayAdapter（））从ViewModel接收属性作为参数，然后返回可以在<$ c上设置的值$ c> this.View.Property 。

this.View.Property should refer to the property that changes whenever the list of devices changes. The third parameter (devices => new ArrayAdapter()) receives the property from the ViewModel as an argument, you then return a value that can be set on the this.View.Property.

例如：

• ViewModel.Count 是字符串


• View.Property 是 int

• ViewModel.Count is a string
• View.Property is an int

这样的绑定：

this.OneWayBind(this.ViewModel.Count, this.View.Property, count => int.Parse(count));

第三个参数可以是接受参数的函数或lambda的ViewModel属性的类型，并返回该视图属性的类型的值。

The third parameter can be a function or lambda that accepts an argument of the type of the ViewModel property and returns a value of the type of the view property.

这篇关于Xamarin.Android和Spinner与ReactiveUI绑定的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！