对ViewModelBase的改进

Question

每次我编写MVVM应用程序(比如每4-6个月一次)，我都会重写我的ViewModelBase类。这有很多原因，但假设我无法访问以前的代码，之前的代码是为客户端构建的，不是我的代码，或者我正在使用别人的机器，但仍然没有代码。

因此，我重写了基本的INotifyPropertyChanged实现，我认为每次都会有所不同。以下是我今天想出的：

public class ViewModelBase : INotifyPropertyChanged
{
    protected void OnPropertyChanged<T>(Expression<Func<T>> expression)
    {
        var property = (MemberExpression)expression.Body;
        this.OnPropertyChanged(property.Member.Name);
    }

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

    public event PropertyChangedEventHandler PropertyChanged;
}

我希望得到一个简单而又小的好实现，以及对此的任何改进(在ViewModelBase中还需要哪些其他功能？)那就太好了。

Answer 1

我已经用了一段时间了：

public abstract class PropertyChangedBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void RaisePropertyChanged(string propertyName)
    {
        var propertyChanged = this.PropertyChanged;

        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    protected bool SetProperty<T>(ref T backingField, T Value, Expression<Func<T>> propertyExpression)
    {
        var changed = !EqualityComparer<T>.Default.Equals(backingField, Value);

        if (changed)
        {
            backingField = Value;
            this.RaisePropertyChanged(ExtractPropertyName(propertyExpression));
        }

        return changed;
    }

    private static string ExtractPropertyName<T>(Expression<Func<T>> propertyExpression)
    {
        var memberExp = propertyExpression.Body as MemberExpression;

        if (memberExp == null)
        {
            throw new ArgumentException("Expression must be a MemberExpression.", "propertyExpression");
        }

        return memberExp.Member.Name;
    }
}

我可以这样写我的财产：

    private int id;

    public int Id
    {
        get
        {
            return this.id;
        }

        set
        {
            this.SetProperty(ref this.id, value, () => this.Id);
        }
    }

Answer 2

特别是与NotifyPropertyChanged相关的，我发现VerifyPropertyName是有用的。

来自乔希·史密斯的网站：实现INotifyPropertyChanged的基类

[Conditional("DEBUG"), DebuggerStepThrough()]
public void VerifyPropertyName(string propertyName)
{
// Verify that the property name matches a real,  
// public, instance property on this object.
if (TypeDescriptor.GetProperties(this)(propertyName) == null) {
    string msg = "Invalid property name: " + propertyName;

    if (this.ThrowOnInvalidPropertyName) {
        throw new Exception(msg);
    } else {
        Debug.Fail(msg);
    }
}
}

Answer 3

这是很多年后的事了，但是现在任何一个偶然发现这件事的人都应该知道MVVM Light和PropertyChanged.Fody。

两者都在nuget.org上

• http://www.mvvmlight.net/
• https://github.com/Fody/PropertyChanged