Question

我目前正在尝试掌握MVVM的概念。因此，我已经阅读了几个博客并查看了一些项目。但是，我仍然不知道如何应用这个概念。

现在，我正在尝试将String的ObservableCollection绑定到ListBox，以便逐行列出它们的值。我的 ViewModel 目前看起来像这样：

namespace TestApp.ViewModel
{
    class StatusViewModel : NotifyPropertyChanged
    {
        private string _newMsg;
        private readonly ObservableCollection<string> _history = new ObservableCollection<string>();

        public string Print
        {
            get { return _newMsg; }
            set
            {
                _newMsg = value;
                RaisePropertyChangedEvent("History");
                AddToHistory(_newMsg);
            }
        }

        public IEnumerable<string> History
        {
            get { return _history; }
        }

        private void AddToHistory(string item)
        {
            if (!_history.Contains(item))
                _history.Add(item);
        }
    }
}

namespace TestApp.ViewModel
{
    public class NotifyPropertyChanged : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void RaisePropertyChangedEvent(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

在View中，我想将ListBox绑定到History。这是我的XAML：

<UserControl x:Class="TestApp.View.StatusView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:vm="clr-namespace:TestApp.ViewModel" mc:Ignorable="d">
    <UserControl.Resources>
        <vm:StatusView x:Key="statusView"/>
    </UserControl.Resources>
    <Grid DataContext="{StaticResource statusView}">
        <GroupBox Header="StatusView">
            <ListBox x:Name="StatusListBox" ItemsSource="{Binding History, Source={StaticResource statusView}}"/>
        </GroupBox>
    </Grid>
</UserControl>

当我启动TestApp时，我需要访问StatusViewModel的实例才能将字符串添加到我的ObservableCollection中。我想知道如何做到这一点：

using TestApp.ViewModel;

namespace TestApp.Controller
{
    public partial class Startup
    {
        private void StartTestApp()
        {
            // from where do I get my 'statObj' in order to do:
            statObj.Print = "something";
        }
    }
}

如何将StatusViewModel对象中的Strings的ObservableCollection绑定到Listbox？

更新

谢谢大家的好评！现在，我了解到我需要保存ViewModel的实例，以便从 View 和 Controller 中访问它。但是，我仍然在努力解决如何以正确的方式做到这一点。## Heading ##

现在，我开始在用户控件的代码隐藏中创建实例。虽然它有效，但我不喜欢我必须在我的视图中引用ViewModel。我想，这是MVVM 不的重点。

此外，我想知道如何在View之外访问我新实例化的StatusViewModel状态，例如在名为 Controller 的其他命名空间中。

using System.Windows.Controls;
using TestApp.ViewModel;

namespace TestApp.View
{
    /// <summary>
    /// Interaction Logic for StatusView.xaml
    /// </summary>
    public partial class StatusView : UserControl
    {
        public StatusView()
        {
            InitializeComponent();

            this.DataContext = new StatusViewModel();
        }

        public TestApp.ViewModel.StatusViewModel State
        {
            get { return (DataContext as TestApp.ViewModel.StatusViewModel); }
        }
    }
}

Answer 1

将您的XAML更改为：

<UserControl x:Class="TestApp.View.Status"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:vm="clr-namespace:TestApp.ViewModel" mc:Ignorable="d">
<UserControl.DataContext>
    <vm:Status />
</UserControl.DataContext>
<Grid>
    <GroupBox Header="Status">
        <ListBox x:Name="StatusListBox" ItemsSource="{Binding History}"/>
    </GroupBox>
</Grid>

访问您的viemodel的代码应该包含：

Status status = DataContext as Status;
if (status != null)
   status.Print = "Hello";

然后它似乎工作： enter image description here

如果要访问此用户控件的Status实例，请向用户控件添加属性：

public TestApp.ViewModel.Status State // Status gives probably naming conflict
{ 
    get
    {
        return (DataContext as TestApp.ViewModel.Status);
    }
}

Answer 2

尝试

public ObservableCollection<string> History
{
    get { return _history; }
}
private void AddToHistory(string item)
{
    if (!History.Contains(item)) History.Add(item);
}

将ObservableCollection的字符串绑定到WPF中的ListBox

2 个答案: