[英]Shorter code to trigger property changed events
我有一个包含数十个属性的类,需要引发属性更改事件,目前我的代码看起来像
public class Ethernet : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string timeStamp;
public string TimeStamp
{
get { return timeStamp; }
set
{
timeStamp = value;
if(PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("TimeStamp"));
}
}
}
在 C# 中是否有更短的方法来编写这种代码,我对每个属性都做了过多的复制/粘贴操作,我觉得必须有更好的方法。
引用的代码不是写的线程安全的。 请参阅实现 INotifyPropertyChanged 的模式? 为什么下面的代码更好,以及在接受的回复中指向 Eric Lippert 博客的链接为什么故事没有就此结束。
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs("TimeStamp"));
有关实际问题的答案,请参阅实现 INotifyPropertyChanged - 是否存在更好的方法? 包括这个 C# 6.0 快捷方式。
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("TimeStamp"));
看看这个答案: https : //stackoverflow.com/a/2339904/259769
我的代码提供和扩展方法来替换大部分设置代码,让我们将代码缩短为:
public class Ethernet : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string timeStamp;
public string TimeStamp
{
get { return timeStamp; }
set { this.NotifySetProperty(ref timeStamp, value, () => this.TimeStamp); }
}
}
这段代码的另一个明显优点是它立即变成了针对属性名称的强类型。
在 MVVM 模式中,经常使用属性更改 / ing,典型的基本解决方案如下:
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void FirePropertyChanged([CallerMemberName] string propertyName = null)
{
if (propertyName == null)
throw new ArgumentNullException("propertyName");
try
{
this.OnPropertyChanged(propertyName);
}
catch (Exception exception)
{
Trace.TraceError("{0}.OnPropertyChanged threw {1}: {2}", this.GetType().FullName, exception.GetType().FullName, exception);
}
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class Ethernet : ViewModelBase
{
private DataTime timeStamp;
public DateTime TimeStamp
{
get
{
return timeStamp;
}
set
{
timeStamp = value;
FirePropertyChanged();
}
}
}
我爱上了这门课:
[Serializable]
public class PropertyChangedBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual bool SetProperty<T>(T value, ref T field, Expression<Func<object>> property)
{
return SetProperty(value, ref field, GetPropertyName(property));
}
protected virtual bool SetProperty<T>(T value, ref T field, [CallerMemberName] string propertyName = null)
{
if (field == null || !field.Equals(value))
{
field = value;
OnPropertyChanged(propertyName);
return true;
}
return false;
}
public void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public void OnPropertyChanged(Expression<Func<object>> property)
{
OnPropertyChanged(GetPropertyName(property));
}
protected string GetPropertyName(Expression<Func<object>> property)
{
var lambda = property as LambdaExpression;
MemberExpression memberExpression;
var unaryExpression = lambda.Body as UnaryExpression;
if (unaryExpression != null)
{
memberExpression = unaryExpression.Operand as MemberExpression;
}
else
{
memberExpression = (MemberExpression) lambda.Body;
}
var propertyInfo = memberExpression?.Member as PropertyInfo;
return propertyInfo?.Name ?? string.Empty;
}
}
这样做的一个巨大优势是它会检查值是否发生了变化。 这将最小化对视图的更新调用。 对于您的示例,它可能如下所示:
public class Ethernet : PropertyChangedBase
{
private string _timeStamp;
public string TimeStamp
{
get { return _timeStamp; }
set { SetProperty(value, ref _timeStamp); }
}
}
如果您希望它真的很舒服,您可以为此编写一个代码片段。 这将是片段部分:
<Snippet>
<Declarations>
<Literal>
<ID>PropertyName</ID>
<Type>String</Type>
<ToolTip>The property name</ToolTip>
<Default>NewProperty</Default>
</Literal>
<Literal>
<ID>PropertyType</ID>
<Type>
</Type>
<ToolTip>Replace with the type of the property</ToolTip>
<Default>string</Default>
</Literal>
<Object>
<ID>PrivateVariable</ID>
<Type>Object</Type>
<ToolTip>The name of the private variable</ToolTip>
<Default>newPropertyValue</Default>
</Object>
</Declarations>
<Code Language="csharp" Kind="method decl"><![CDATA[ private $PropertyType$ _$PrivateVariable$;
public $PropertyType$ $PropertyName$
{
get { return _$PrivateVariable$; }
set
{
SetProperty(value, ref _$PrivateVariable$);
}
}]]></Code>
</Snippet>
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