我有以下类(class):
public class AndSpecification<TEntity> : ISpecification<TEntity>
{
protected ISpecification<TEntity> First { get; private set; }
protected ISpecification<TEntity> Second { get; private set; }
public bool IsSatisfiedBy(TEntity entity)
{
return First.IsSatisfiedBy(entity) && Second.IsSatisfiedBy(entity);
}
public AndSpecification(ISpecification<TEntity> first, ISpecification<TEntity> second)
{
Contract.Requires(first != null);
Contract.Requires(second != null);
Contract.Ensures(First != null);
Contract.Ensures(Second != null);
First = first;
Second = second;
}
}
请注意,我使用 Contract.Ensures()
确保调用构造函数后,First
和 Second
永远不会为空。然而,Code Contracts 在 IsSatisfiedBy()
中给我一个警告方法实现:CodeContracts: Possibly calling a method on a null reference 'this.First'
(与 Second
相同)。无法弄清楚出了什么问题,是我还是静态检查器?
最佳答案
您似乎缺少一些契约和对象不变量。我把你的代码放在上面并对它运行代码契约(Contract)静态分析,并得到了你所得到的。然后,我按照自己的方式完成代码,以获得满足静态分析器要求的实现。
[ContractClass(typeof(ISpecificationContracts<>))]
public interface ISpecification<TEntity>
where TEntity : class
{
bool IsSatisfiedBy(TEntity entity);
}
[ContractClassFor(typeof(ISpecification<>))]
abstract class ISpecificationContracts<TEntity>
: ISpecification<TEntity> where TEntity : class
{
public bool IsSatisfiedBy(TEntity entity)
{
Contract.Requires(entity != null);
throw new NotImplementedException();
}
}
public class AndSpecification<TEntity>
: ISpecification<TEntity> where TEntity : class
{
private readonly ISpecification<TEntity> _first;
private readonly ISpecification<TEntity> _second;
protected ISpecification<TEntity> First {
get
{
Contract.Ensures(Contract.Result<ISpecification<TEntity>>() != null);
return _first;
}
}
protected ISpecification<TEntity> Second
{
get
{
Contract.Ensures(Contract.Result<ISpecification<TEntity>>() != null);
return _second;
}
}
public bool IsSatisfiedBy(TEntity entity)
{
return First.IsSatisfiedBy(entity) && Second.IsSatisfiedBy(entity);
}
public AndSpecification(ISpecification<TEntity> first,
ISpecification<TEntity> second)
{
Contract.Requires(first != null);
Contract.Requires(second != null);
Contract.Ensures(_first == first);
Contract.Ensures(_second == second);
_first = first;
_second = second;
}
[ContractInvariantMethod]
[System.Diagnostics.CodeAnalysis.SuppressMessage(
"Microsoft.Performance",
"CA1822:MarkMembersAsStatic",
Justification = "Required for code contracts.")]
private void ObjectInvariant()
{
Contract.Invariant(_first != null);
Contract.Invariant(_second != null);
}
}
关于c# - 代码契约(Contract)静态检查器 : Possibly calling a method on a null reference — why?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26160866/