通过INotifyPropertyChanged写入文本框不工作

我有一个问题，一个属性调用INotifyPropertyChanged事件。我创建了一个简单的概念WPF程序，它试图通过一个按钮来写入一个文本框，该按钮调用一个函数来更新属性(ViewModel1StringProperty)。该属性被绑定到文本框，并且该属性调用一个INotifyPropertyChanged事件。我已经为文本框添加了这个text属性:

Text="{Binding ViewModel1StringProperty, UpdateSourceTrigger=PropertyChanged}"

但是，当单击按钮时，文本框仍然没有更新。需要注意的一点是，按钮调用iccommand，然后最终通过函数调用(TestFunction1)更新属性。我相信这个命令是正确地绑定到按钮，但我不确定。

对此问题的任何见解都将非常感谢。

ViewModel代码:

    namespace WpfApplicationOnPropertyChanged.ViewModel
    {
        class ViewModel1 : INotifyPropertyChanged
        {
            #region Fields
            string _viewModel1StringProperty;
            public event PropertyChangedEventHandler PropertyChanged;
            #endregion
        protected void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new  PropertyChangedEventArgs(propertyName));
            }
        }
        #region Properties
        public string ViewModel1StringProperty
        {
            get
            {
                return _viewModel1StringProperty;
            }
            set
            {
                _viewModel1StringProperty = value;
                NotifyPropertyChanged("ViewModel1StringProperty");
            }
        }
        #endregion
        #region Commands
        public ICommand ViewModelICommandField1
        {
            get
            {
                return new ViewModelICommand(TestFunction1);
            }
        }
        #endregion
        #region Functions
        private void TestFunction1()
        {
            ViewModel1StringProperty = "Test1'n";
        }
        #endregion
    }
}

视图代码:

    namespace WpfApplicationOnPropertyChanged.View
    {
        /// <summary>
        /// Interaction logic for View1.xaml
    /// </summary>
    public partial class View1 : UserControl
    {
        #region Fields
        ViewModel1 _viewModel1 = new ViewModel1();
        #endregion
        public View1()
        {
            InitializeComponent();
            this.DataContext = _viewModel1;
        }
    }
}

XAML代码:

    <UserControl x:Class="WpfApplicationOnPropertyChanged.View.View1"
             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:local="clr-namespace:WpfApplicationOnPropertyChanged.View"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TextBox Name="textBox1" HorizontalAlignment="Left" Height="89" Margin="58,62,0,0" Text="{Binding ViewModel1StringProperty, UpdateSourceTrigger=PropertyChanged}" TextWrapping="Wrap" VerticalAlignment="Top" Width="181"/>
        <Button Content="Button1"  Command="{Binding ViewModel1ICommandField1}" HorizontalAlignment="Left" Margin="106,205,0,0" VerticalAlignment="Top" Width="75"/>
    </Grid>
</UserControl>

ICommand代码:

    namespace WpfApplicationOnPropertyChanged.ViewModel
    {
        class ViewModelICommand : ICommand
        {
           private Action _action;
        public ViewModelICommand(Action action)
        {
            _action = action;
        }    
        public void Execute(object parameter)
        {
            _action();
        }
        public bool CanExecute(object parameter)
        {
            return true;
        }
        public event EventHandler CanExecuteChanged
        {
            add { }
            remove { }
        }
    }
}