我有不同的属性,可以提供一个值,我想返回第一个满足指定条件。调用谓词抛出NullReferenceException
问题是,当其中一个来源是class
,是null
,我得到不设置到对象的实例很好对象引用。。
我无法找到属性来检查当前提供程序的无效性,无论是Func<T,bool>
还是Expression<Func<Media,T>>
。
你知道我该如何检查函数目标的无效性?
public int TempoInteger
{
get
{
double result;
// In this case, AudioSummary is a class that can be null
if (TryGetValue(out result, s => s > 0.0d, s => s.TempoBass, s => s.AudioSummary.Tempo))
{
return (int)Math.Round(result);
}
return -1;
}
}
private AudioSummary AudioSummary {get; set;}
/// <summary>
/// Tries to get a value from multiple expressions, first expression value that satisfies the predicate will be returned. If no value satisifes the predicate the default value of <typeparamref name="T"/> will be returned.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="result"></param>
/// <param name="predicate"></param>
/// <param name="expressions"></param>
/// <returns></returns>
private bool TryGetValue<T>(out T result, Func<T, bool> predicate, params Expression<Func<Media, T>>[] expressions)
{
foreach (var expression in expressions)
{
Func<Media, T> func = expression.Compile();
// 'System.NullReferenceException' occurs here when AudioSummary is null
T t = func(this);
var b = predicate(t);
if (b)
{
result = t;
return true;
}
}
result = default(T);
return false;
}
public sealed class AudioSummary
{
[JsonProperty("tempo")]
public double Tempo { get; set; }
// ...
}
我没有看到'AudioSummary'代码,除了评论... – Blorgbeard
我添加代码的属性和类的修剪定义。 – Aybe