A System.Collections.Generic.Dictionary
is throwing KeyNotFoundException
,但我看不到应该缺少哪个键。我如何确定这一点?
7 回答
自定义异常:
class WellknownKeyNotFoundException : KeyNotFoundException
{
public WellknownKeyNotFoundException(object key, string message)
: this(key, message, null) { }
public WellknownKeyNotFoundException(object key, string message, Exception innerException)
: base(message, innerException)
{
this.Key = key;
}
public object Key { get; private set; }
}
方便的扩展方法:
public TValue GetValue<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key)
{
try
{
return dic[key];
}
catch (KeyNotFoundException ex)
{
throw new WellknownKeyNotFoundException((object)key, ex.InnerException);
}
}
用法:
var foo = new Foo();
var bar = new Bar();
IDictionary<Foo, Bar> dic = new Dictinary<Foo, Bar>
{
{ foo, bar }
};
try
{
dic.GetValue(foo);
}
catch (WellknownKeyNotFoundException ex)
{
var key = (Foo)ex.Key;
Assert.AreEqual(foo, key); // should be
}
没有办法从异常中看出这一点。您需要为此实施自己的解决方案。
如果您可以自定义声明字典的实现,则可以轻松地将 System.Collections.Generic.Dictionary 替换为自定义类型,引发更好的 KeyNotFoundException。虽然这与 abatishchev 的答案相似,但我不喜欢他介绍的扩展方法,因为这意味着我们有两种不同的方法来实现完全相同的事情。如果可能,应该避免这种情况。我通过使用“NiceDictionary”解决了这个问题,它可以像原来用作基类的字典一样使用。实现几乎是微不足道的:
/// <summary>
/// This is a nice variant of the KeyNotFoundException. The original version
/// is very mean, because it refuses to tell us which key was responsible
/// for raising the exception.
/// </summary>
public class NiceKeyNotFoundException<TKey> : KeyNotFoundException
{
public TKey Key { get; private set; }
public NiceKeyNotFoundException(TKey key, string message)
: base(message, null)
{
this.Key = key;
}
public NiceKeyNotFoundException(TKey key, string message, Exception innerException)
: base(message, innerException)
{
this.Key = key;
}
}
/// <summary>
/// This is a very nice dictionary, because it throws a NiceKeyNotFoundException that
/// tells us the key that was not found. Thank you, nice dictionary!
/// </summary>
public class NiceDictionary<TKey, TVal> : Dictionary<TKey, TVal>
{
public new TVal this[TKey key]
{
get
{
try
{
return base[key];
}
catch (KeyNotFoundException knfe)
{
throw new NiceKeyNotFoundException<TKey>(key, knfe.Message, knfe.InnerException);
}
}
set
{
try
{
base[key] = value;
}
catch (KeyNotFoundException knfe)
{
throw new NiceKeyNotFoundException<TKey>(key, knfe.Message, knfe.InnerException);
}
}
}
}
如前所述,您可以像使用原始字典一样使用它。由于重写的数组运算符([]),它神奇地起作用。
你不能只看异常。抛出异常时,您必须闯入调试器( Visual Studio 中的Debug -> Exceptions... )并查看已访问的键。或者,您可以在代码中捕获异常并将其打印出来(例如到控制台)。
使用调试器(如果需要,请检查 Debug->Exceptions 中的 ThrowOnCatch)并查看
System.Collections.Generic.KeyNotFoundException 已被抛出
如果您将 DotNet Core 与 Xamarin Studio 一起使用并且收到此错误,您可以检查密钥是否存在,并满足以下条件:
if (Application.Current.Properties.ContainsKey("userCredentials")) {
//now process...
}
您会认为他们可以将尝试的密钥添加到 exception.data
这就是我所做的
public static void SetGlobals()
{
string currentKey = "None";
try
{
currentKey = "CurrentEnvironment";
Globals.current_environment = Settings[currentKey];
currentKey = "apiUrl";
Globals.api_url = Settings[currentKey];
currentKey = "whatever";
Globals.whatever= Settings[currentKey];
if (AppDomain.CurrentDomain.GetData(".devEnvironment") as bool? == true)
Globals.api_url = "http://localhost:59164/api";
}
catch(KeyNotFoundException)
{
DBClass.logEvent("Error", "AppSettings", "Missing Setting: " + currentKey);
}
}