WPF C# PropertyChanged 始终为空

Question

我已经尝试了一段时间并决定看看是否有人可以提供帮助，我在 StatusInfo 的构造函数中设置了 DataContext = this 但没有用。当我将字符串写入 ScreenStatusBarText 时，它会调用 OnPropertyChanged 方法，但每次 PropertyChanged 值为 null。我在屏幕底部的状态块。我在这个堆栈面板上方有一个选项卡部分，其中包含许多使用绑定和工作的组件。

屏幕代码

<StackPanel Margin="0,1047,0,0">
  <Grid Name="StatusBarItemGrid">
  <TextBlock Name="StatusBarText" Text="may the force be with you"   VerticalAlignment="Center" HorizontalAlignment="Stretch" />
  </Grid>
 </StackPanel>

数据模型：

public partial class StatusInfo :  INotifyPropertyChanged
{

    private string screenStatusBarText;

    public StatusInfo()
    {
        BindScreenStatusBarText();
        screenStatusBarText = "Initialized";
    }

    public string ScreenStatusBarText
    {
        get { return screenStatusBarText; }
        set
        {
            screenStatusBarText = value;
            OnPropertyChanged("StatusBarText");
        }
    }

    private void BindScreenStatusBarText()
    {

        Binding b = new Binding();
        b.Source = screenStatusBarText;
        b.Mode = BindingMode.OneWay;
        b.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        b.Path = new PropertyPath("StatusBarText");
        MainWindow.mainWindow.StatusBarText.SetBinding(TextBlock.TextProperty, b);

        MainWindow.mainWindow.StatusBarText.DataContext = this;
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

我的主要 :

public partial class MainWindow : Window
{
    public static StatusInfo status;
    public MainWindow()
    {
        InitializeComponent();
        SourceInitialized += MainWindow_SourceInitialized;
    }

    private void MainWindow_SourceInitialized(object sender, EventArgs e)
    {
        SetUpDisplay();
    }

    private void SetUpDisplay()
    {
            status = new StatusInfo();
    }
}

Answer 1

我认为您将很难在代码隐藏中进行绑定。

话说回来，关于为什么你的PropertyChanged值为null。您只是打错了字，as-is 您是在通知订阅者不存在的属性已更改。避免此类拼写错误的一种解决方案是使用 nameof。

public string ScreenStatusBarText
{
    get { return screenStatusBarText; }
    set
    {
        screenStatusBarText = value;
        OnPropertyChanged(nameof(ScreenStatusBarText));
    }
}

我突然想到你可能也意味着你的活动是空的。这仅仅意味着您没有任何订阅者。参见 Why is my "Event" always null?。

private void OnPropertyChanged(string propertyName)
{
    var handler = PropertyChanged;

    if (handler != null) // I have a subscriber.
        handler(this, new PropertyChangedEventArgs(propertyName));
}

Answer 2

在 XAML 中设置绑定而不是隐藏代码：

<TextBlock Text="{Binding ScreenStatusBarText}" />

并使用像

这样的视图模型

public class StatusInfo : INotifyPropertyChanged
{
    private string screenStatusBarText = "Initialized";

    public string ScreenStatusBarText
    {
        get { return screenStatusBarText; }
        set
        {
            screenStatusBarText = value;
            OnPropertyChanged(nameof(ScreenStatusBarText));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this,
            new PropertyChangedEventArgs(propertyName));
    }
}

将视图模型的实例 class 分配给 MainWindow 的 DataContext：

private readonly StatusInfo statusInfo = new StatusInfo();

public MainWindow()
{
    InitializeComponent();
    DataContext = statusInfo;
}

您现在可以在以后随时访问视图模型 class，例如在 MainWindow 的一个元素的事件处理程序中：

statusInfo.ScreenStatusBarText = "Something";

WPF C# PropertyChanged 始终为空

WPF C# PropertyChanged always null

c#

data-binding

wpf

textblock

inotifypropertychanged