C# · 12月 23, 2021

c# – 该字段如何为空?

我得到一个空的异常,但该字段已初始化为空列表.那么怎么可能是null?

该方法的第二行发生错误(在_hydratedProperties上):

protected virtual void NotifyPropertyChanged<T>(Expression<Func<T>> expression){ string propertyName = GetPropertyName(expression); if (!this._hydratedProperties.Contains(propertyName)) { this._hydratedProperties.Add(propertyName); }}

这就是这个领域如何被宣布:

public abstract class EntityBase<TSubclass> : INotifyPropertyChanged where TSubclass : class{ private List<string> _hydratedProperties = new List<string>();

这是它的设置:

public Eta Eta { get { return this._eta; } set { this._eta = value; NotifyPropertyChanged(() => this.Eta); } }

这是完整的课程(删除了注释和非相关部分):

[DataContract]public abstract class EntityBase<TSubclass> : INotifyPropertyChanged where TSubclass : class{ private List<string> _hydratedProperties = new List<string>(); public bool IsPropertyHydrated(string propertyName) { return this._hydratedProperties.Contains(propertyName); } public event PropertyChangedEventHandler PropertyChanged; protected virtual void NotifyPropertyChanged<T>(Expression<Func<T>> expression) { string propertyName = GetPropertyName(expression); if (!this._hydratedProperties.Contains(propertyName)) { this._hydratedProperties.Add(propertyName); } PropertyChangedEventHandler handler = PropertyChanged; if (handler != null) { handler(this,new PropertyChangedEventArgs(propertyName)); } } public string GetPropertyName<T>(Expression<Func<T>> expression) { MemberExpression memberExpression = (MemberExpression)expression.Body; return memberExpression.Member.Name; }}

派生类:

[DataContract]public class Bin : EntityBase<Bin>{ private Eta _eta; [DataMember] public Eta Eta { get { return this._eta; } set { this._eta = value; NotifyPropertyChanged(() => this.Eta); } }}解决方法 以下是线索: [DataContract]

对. DataContractSerializer does not call any constructor.相反,它使用FormatterServices.GetUninitializedObject来创建将被反序列化的对象.这将绕过构造函数调用.

您的初始化程序:

private List<string> _hydratedProperties = new List<string>();

被编译器转换为隐式的默认构造函数.

作为解决方法,您可以使用a deserialization callback with OnDeserializingAttribute:

[DataContract]public abstract class EntityBase<TSubclass> : INotifyPropertyChanged where TSubclass : class{ private List<string> _hydratedProperties; protected EntityBase() { Init(); } private void Init() { _hydratedProperties = new List<string>() } [OnDeserializing] private void OnDeserializing(StreamingContext context) { Init(); } // … rest of code here}