C# PropertyChanged仅在第一个事件上为null

我正在准备用WPF编写代码。所以我想出了一些基本的模拟代码来让自己开始。我有一个简单的WPF界面，其中有一个日期选择器、一些文本框和复选框

我想对INotifyPropertyChanged界面做的是，当我单击按钮时，我的文本框将显示“Hello Kevin”。为了测试它，我首先说我的字符串将以“Initially”开头，当我的方法返回时，它将返回“Hello Kevin”

我还应该指定我编写了一个模拟异步代码，该代码将调用服务器并在数据库中获取名称。这段代码运行得很好。问题是，当我第一次点击按钮时，PropretyChanged是空的。但是，当我再次单击它时，它会显示我想看到的消息

它让我想知道这个方法是否真的像我预期的那样工作，所以我用Console.WriteLine方法做了一些基本的测试，它只会显示我目前正在寻找的结果

下面，您可以找到我用于这个小软件的所有类：

public class ViewModelCommonBase : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged;

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

public class SimpleViewModel : ViewModelCommonBase
{
    #region fields
    private bool _isHealthCareEnabled=false;

    private bool _isBenefits=false;

    private bool _is401kEnabled=false;

    private DateTime _birth;

    #endregion

    #region Properties

    public int Age
    {
        get { return  (int)((DateTime.Now - Birth).TotalDays)/365 ;}

    }
    public bool IsHealthCareEnabled
    {
        get { return _isHealthCareEnabled; }
        set { _isHealthCareEnabled = value; }
    }


    public bool IsBenefitsEnabled
    {
        get { return _isBenefits; }
        set
        {
            if (_isBenefits != value)
            {
                _isBenefits = value;
                OnPropertyChanged("IsBenefitsEnabled");
            }
        }
    }

    public bool Is401kEnabled
    {
        get { return _is401kEnabled; }
        set { _is401kEnabled = value; }
    }


    public DateTime Birth
    {
        get { return _birth; }
        set
        {
            if (_birth != value)
            {
                _birth = value;
                OnPropertyChanged("Birth");
                OnPropertyChanged("Age"); 
            }
        }
    }

    #endregion      
}

public class AsyncServerStud :ViewModelCommonBase
{
    private string _nameOfPerson="Initial";

    public string NameOfPerson
    {
        get { return _nameOfPerson; }
        set
        {
            if (_nameOfPerson != value)
            {
                _nameOfPerson = value;
                OnPropertyChanged("NameOfPerson");

            }
        }
    }


    public async void FindNameOfPerson()
    {
        var result = await FindNameOfPersonAsync("Kevin");
        NameOfPerson = result;
        Console.WriteLine(NameOfPerson);
    }

    private Task<string> FindNameOfPersonAsync(string name)
    {
        return Task.Factory.StartNew(() => SearchNameOfPerson(name));
    }

    private string SearchNameOfPerson(string name)
    {
        Thread.Sleep(6000);
        return "Hello, " + name;
    }


}

    public class WPFViewModelPage
{
    public SimpleViewModel SimpleViewModel { get; set; }
    public AsyncServerStud MockServer { get; set; }


}

---

我对你的申请做了以下更改，它对我有效。请尝试以下更改

将

DataContext

分配到

Window

而不是将其设置为

Grid

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:WpfApplication1"
        Title="MainWindow"
        Height="350"
        Width="525">
    <Window.DataContext>
        <vm:WPFViewModelPage />
    </Window.DataContext>
    <Window.Resources>
        <vm:WPFViewModelPage x:Key="viewModel" />
    </Window.Resources>
    <Grid Name="myGrid">
        <CheckBox x:Name="chkBenefits"
                  Content="Has Benefits ?"
                  HorizontalAlignment="Left"
                  Margin="62,45,0,0"
                  VerticalAlignment="Top"
                  IsChecked="{Binding SimpleViewModel.IsBenefitsEnabled}" />
        <StackPanel IsEnabled="{Binding SimpleViewModel.IsBenefitsEnabled}">
            <CheckBox Content="Health care"
                      HorizontalAlignment="Left"
                      Margin="85,86,0,0"
                      VerticalAlignment="Top"
                      IsEnabled="{Binding SimpleViewModel.IsBenefitsEnabled}"
                      IsChecked="{Binding SimpleViewModel.IsHealthCareEnabled}" />
            <DatePicker Name="mydatePicker"
                        DisplayDate="{Binding SimpleViewModel.Birth}" />
            <TextBlock TextWrapping="Wrap"
                       Text="{Binding SimpleViewModel.Age}" />
            <Button Content="Button"
                    Click="Button_Click" />
            <TextBox Name="mySecondTextBox"
                     Height="23"
                     TextWrapping="Wrap"
                     Text="{Binding MockServer.NameOfPerson }" />
        </StackPanel>
    </Grid>
</Window>

在

按钮中添加以下代码\u单击
方法

private void Button_Click(object sender, RoutedEventArgs e)
{
    WPFViewModelPage dataContext = this.DataContext as WPFViewModelPage;
    dataContext.MockServer.FindNameOfPerson();
}

PropertyChanged
总是空的，这似乎很奇怪。好的，只要您设置了
DataContext
，它就会被分配到。你是用一种奇怪的方式设置的吗？加上它，你就不会点击按钮了吗？如果你想要一个异步get，为什么不直接使用异步get呢。甚至还有一个优先级绑定。是的，谢谢，这是我在编辑之前更改的。别误会我的意思，我非常感谢你花时间给我一个答案。当我在XAML中进行数据绑定时，我想知道为什么数据绑定不能正常工作。实际上，不管我说了什么，我没有将数据上下文放在click事件中，为什么要这样做？我只在XAML中设置DataContext，并从Button_click访问相同的DataContext。我在回答中更新了整个XAML。请检查为什么XAML不工作，因为您正在将DataContext设置为网格，如DataContext=“{Binding Source={StaticResource viewModel}}”，所以当然窗口DataContext将为空。您可以通过访问按钮中的myGrid.DataContext来解决此问题
<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:WpfApplication1"
        Title="MainWindow"
        Height="350"
        Width="525">
    <Window.DataContext>
        <vm:WPFViewModelPage />
    </Window.DataContext>
    <Window.Resources>
        <vm:WPFViewModelPage x:Key="viewModel" />
    </Window.Resources>
    <Grid Name="myGrid">
        <CheckBox x:Name="chkBenefits"
                  Content="Has Benefits ?"
                  HorizontalAlignment="Left"
                  Margin="62,45,0,0"
                  VerticalAlignment="Top"
                  IsChecked="{Binding SimpleViewModel.IsBenefitsEnabled}" />
        <StackPanel IsEnabled="{Binding SimpleViewModel.IsBenefitsEnabled}">
            <CheckBox Content="Health care"
                      HorizontalAlignment="Left"
                      Margin="85,86,0,0"
                      VerticalAlignment="Top"
                      IsEnabled="{Binding SimpleViewModel.IsBenefitsEnabled}"
                      IsChecked="{Binding SimpleViewModel.IsHealthCareEnabled}" />
            <DatePicker Name="mydatePicker"
                        DisplayDate="{Binding SimpleViewModel.Birth}" />
            <TextBlock TextWrapping="Wrap"
                       Text="{Binding SimpleViewModel.Age}" />
            <Button Content="Button"
                    Click="Button_Click" />
            <TextBox Name="mySecondTextBox"
                     Height="23"
                     TextWrapping="Wrap"
                     Text="{Binding MockServer.NameOfPerson }" />
        </StackPanel>
    </Grid>
</Window>

    public class WPFViewModelPage
    {
        public SimpleViewModel SimpleViewModel { get; set; }
        public AsyncServerStud MockServer { get; set; }

        public WPFViewModelPage()
        {
            this.SimpleViewModel = new SimpleViewModel();
            this.MockServer = new AsyncServerStud();
        }
    }

private void Button_Click(object sender, RoutedEventArgs e)
{
    WPFViewModelPage dataContext = this.DataContext as WPFViewModelPage;
    dataContext.MockServer.FindNameOfPerson();
}