Xamarin Forms + Mvvmcross绑定命令不起作用

Question

我是一个新的Xamarin表格。我用mvvmcross创建了一个简单的xamarin表单项目（Hello World非常简单，适合开始），但是当我实现绑定命令时，并没有影响标签的更改文本。我的Xaml代码和ViewModel如下。

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:vm="clr-namespace:MvvmCross.ViewModels;assembly=MvvmCross"
         x:Class="MvvmCross.Views.HelloView">
<StackLayout>
    <StackLayout.BindingContext>
        <vm:HelloViewModel />
    </StackLayout.BindingContext>
    <Entry  HorizontalOptions="Fill" VerticalOptions="Center" Text="{Binding Name, Mode=TwoWay }"/>
    <Button Text="Hello" HorizontalOptions="Center" VerticalOptions="Center" Command="{Binding HelloCommand}" />
    <Label HorizontalOptions="Fill" VerticalOptions="Center" FontSize="15" Text="{Binding Hello, Mode=TwoWay}" />
</StackLayout>

using MvvmCross.Core.ViewModels;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace MvvmCross.ViewModels
{
   public class HelloViewModel: Core.ViewModels.MvxViewModel
   {
    private string _name;
    public HelloViewModel()
    {
        Hello = "Your name";
    }
    public string Name
    {
        get { return _name; }
        set { _name = value; RaisePropertyChanged(() => Name); }
    }
    private string _hello;

    public string Hello
    {
        get { return _hello; }
        set { _hello = value; RaisePropertyChanged(() => Hello); }
    }

    private ICommand _helloCommand;

    public ICommand HelloCommand
    {
        get { _helloCommand = _helloCommand ?? new MvxCommand(ShowHello); return _helloCommand; }
    }

    private void ShowHello()
    {
        // not change label text so sadly
        Hello = Name.ToString();
        Debug.WriteLine(Hello);
    }
}

}

感谢所有帮助

Answer 1

即使迟到，它也可以帮助别人。

如果您在Xamarin Forms项目上正确设置了MvvmCross（查看[MvvmCross入门] [1]），则无需在视图模型和视图模型中专门设置BindigContext。

关于这个问题，使用按钮的命令绑定的简单示例：

• 视图

  <views:MvxContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                    xmlns:views="clr- namespace:MvvmCross.Forms.Views;assembly=MvvmCross.Forms"
                    x:Class="TestProject.Pages.TestPage">
  <ContentView>
      <StackLayout>
          <Button Text="Test first command!" Command="{Binding TestFirstCommand}"/>
          <Button Text="Test second command!" Command="{Binding TestSecondCommand}"/>
          <Label Text="{Binding AnyText}"/>
      </StackLayout>
  </ContentView>

• 查看模型

  namespace TestProject.ViewModels 
  {
      public class TestViewModel : MvxNavigationViewModel
      {
          private string _AnyTest;
  
          public TestViewModel()
          {
              AnyText = "";
          }
  
          public string AnyText { get => _AnyTest; set => SetProperty(ref _AnyTest, value); }
          public Command TestFirstCommand => new Command(TestFirstCommandMethod);
          public Command TestSecondCommand => new Command(TestSecondCommandMethod);
  
          private void TestFirstCommandMethod()
          {
              AnyText = "Hello!";
          }
          private void TestSecondCommandMethod()
          {
              AnyText = "How are you?";
          }
      }
  }

Answer 2

你有没有设置BindingContext？

在HelloView.xaml.cs中：

public HelloView() {
    BindingContext = new HelloViewModel();
}

我在移动，很难打字..