Question

我已经玩了一段时间并且决定看看是否有人可以提供帮助，我已经在StatusInfo的构造函数中设置了DataContext = this并且无效。当我向ScreenStatusBarText写一个字符串时，它确实调用OnPropertyChanged方法，但每次PropertyChanged值为null。 I我在屏幕底部的状态块。我在这个堆栈面板上方有一个标签部分，它有许多使用绑定和工作的组件。

屏幕代码

HttpClientBuilder builder = HttpClientBuilder.create();

PlainConnectionSocketFactory plainConnectionSocketFactory = new PlainConnectionSocketFactory();

Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register("http", plainConnectionSocketFactory).build();
PoolingHttpClientConnectionManager ccm = new PoolingHttpClientConnectionManager(registry);
        ccm.setMaxTotal(BaseConstant.CONNECTION_POOL_SIZE); // For Example : CONNECTION_POOL_SIZE = 10 for 10 thread parallel execution
        ccm.setDefaultMaxPerRoute(BaseConstant.CONNECTION_POOL_SIZE);
        builder.setConnectionManager((HttpClientConnectionManager) ccm);

HttpClient objHttpClient = builder.build();

数据模型：

<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>

我的主要人物：

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));
    } 
}

Answer 1

在XAML中设置绑定而不是代码隐藏：

<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));
    }
}

将视图模型类的实例分配给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类，例如在MainWindow元素的事件处理程序中：

statusInfo.ScreenStatusBarText = "Something";

Answer 2

我认为你的代码背后的代码将会很困难。

话虽如此，关于为什么PropertyChanged值为空。你只是犯了一个错字，因为你正在告知订阅者不存在的属性已经改变。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));
    }
}

我发现你可能也意味着你的事件是空的。这只是意味着您没有任何订阅者。请参阅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));
}

WPF C＃PropertyChanged始终为null

2 个答案: