如何在WPF/XAML中正确使用INotifyPropertyChanged

我有一个自定义对象,我正试图绑定到一个控件。在这个自定义对象上,我实现了INotifyPropertyChanged接口。我已成功绑定到我的对象和该对象上的属性。

我不明白的是如何从那里开始。我已经做了两天了,但还是不能用。

我的假设是,当我更改绑定到控件的属性时,该属性中设置的值将显示在控件中。但是,无论我对属性做了多少更改,UI的更新都不会超出其初始值。

我以这种方式实现了INotifyPropertyChanged: A base class which implements INotifyPropertyChanged

[Serializable]
public abstract class BindableObject : INotifyPropertyChanged
{
    #region Data

    private static readonly Dictionary<string, PropertyChangedEventArgs> eventArgCache;
    private const string ERROR_MSG = "{0} is not a public property of {1}";

    #endregion // Data

    #region Constructors

    static BindableObject()
    {
        eventArgCache = new Dictionary<string, PropertyChangedEventArgs>();
    }

    protected BindableObject()
    {
    }

    #endregion // Constructors

    #region Public Members

    /// <summary>
    /// Raised when a public property of this object is set.
    /// </summary>
    [field: NonSerialized]
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Returns an instance of PropertyChangedEventArgs for 
    /// the specified property name.
    /// </summary>
    /// <param name="propertyName">
    /// The name of the property to create event args for.
    /// </param>  
    public static PropertyChangedEventArgs
        GetPropertyChangedEventArgs(string propertyName)
    {
        if (String.IsNullOrEmpty(propertyName))
            throw new ArgumentException(
                "propertyName cannot be null or empty.");

        PropertyChangedEventArgs args;

        // Get the event args from the cache, creating them
        // and adding to the cache if necessary.
        lock (typeof(BindableObject))
        {
            bool isCached = eventArgCache.ContainsKey(propertyName);
            if (!isCached)
            {
                eventArgCache.Add(
                    propertyName,
                    new PropertyChangedEventArgs(propertyName));
            }

            args = eventArgCache[propertyName];
        }

        return args;
    }

    #endregion // Public Members

    #region Protected Members

    /// <summary>
    /// Derived classes can override this method to
    /// execute logic after a property is set. The 
    /// base implementation does nothing.
    /// </summary>
    /// <param name="propertyName">
    /// The property which was changed.
    /// </param>
    protected virtual void AfterPropertyChanged(string propertyName)
    {
    }

    /// <summary>
    /// Attempts to raise the PropertyChanged event, and 
    /// invokes the virtual AfterPropertyChanged method, 
    /// regardless of whether the event was raised or not.
    /// </summary>
    /// <param name="propertyName">
    /// The property which was changed.
    /// </param>
    protected void RaisePropertyChanged(string propertyName)
    {
        this.VerifyProperty(propertyName);

        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            // Get the cached event args.
            PropertyChangedEventArgs args =
                GetPropertyChangedEventArgs(propertyName);

            // Raise the PropertyChanged event.
            handler(this, args);
        }

        this.AfterPropertyChanged(propertyName);
    }

    #endregion // Protected Members

    #region Private Helpers

    [Conditional("DEBUG")]
    private void VerifyProperty(string propertyName)
    {
        Type type = this.GetType();

        // Look for a public property with the specified name.
        PropertyInfo propInfo = type.GetProperty(propertyName);

        if (propInfo == null)
        {
            // The property could not be found,
            // so alert the developer of the problem.

            string msg = string.Format(
                ERROR_MSG,
                propertyName,
                type.FullName);

            Debug.Fail(msg);
        }
    }

    #endregion // Private Helpers
}

我从上面的类继承,并在派生类中对我的属性执行以下操作:

    public virtual string Name
    {
        get
        {
            return m_strName;
        }
        set
        {
            m_strName = value;
            RaisePropertyChanged("Name");
        }
    }

我的XAML看起来像这样(缩写版本):

<Window x:Class="PSSPECApplication.Windows.Project"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:System="clr-namespace:System;assembly=mscorlib"
    DataContext="{Binding SizingProject, RelativeSource={RelativeSource Self}}">
        <StackPanel VerticalAlignment="Center">
            <TextBox Name="txtProjectName" Text="{Binding Name}" />
        </StackPanel>

您可以看到窗口的数据上下文是一个名为SizingProject的属性。SizingProject属于派生类型(从BindableObject派生),其中包含Name属性并引发PropertyChanged事件处理程序。

在窗口的构造函数中,我填充SizingProject,并设置它的Name属性。

为了测试这一点,我在窗口上还有一个按钮,它触发一个事件,该事件将Name属性设置为与原来不同的内容。但是,当name属性更改时,什么都不会发生。我已经追溯到BindableObject,并且PropertyChanged事件总是设置为null,因此没有处理程序被设置和运行。为什么会这样?

我想通过实现INotifyPropertyChanged并在绑定中使用该类型,可以强制WPF自动设置事件处理程序,然后发生正确的行为?对我来说,我从没见过这种行为。

我发现了问题所在。我需要做的是为我的属性SizingProject创建一个dependencProperty。我做完之后,一切都很顺利。

        public static readonly DependencyProperty SizingProjectProperty =
        DependencyProperty.Register("SizingProject", typeof(Sizing.Project), typeof(Project), new UIPropertyMetadata());

    public Sizing.Project SizingProject
    {
        get
        {
            return (Sizing.Project)GetValue(Project.SizingProjectProperty);
        }
        set
        {
            SetValue(Project.SizingProjectProperty, value);
        }
    }