我的情况很简单。在我的代码中，我有这样的代码:
dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame();
//How to do this?
if (myVariable.MyProperty.Exists)
//Do stuff
因此，基本上我的问题是如何检查(不抛出异常)某个属性在我的动态变量上是可用的。我可以使用GetType()，但我宁愿避免这样做，因为我并不真正需要知道对象的类型。我真正想知道的是是否有一个属性(或方法，如果这使工作更简单的话)可用。指针吗?
当前回答
也许使用反射?
dynamic myVar = GetDataThatLooksVerySimilarButNotTheSame();
Type typeOfDynamic = myVar.GetType();
bool exist = typeOfDynamic.GetProperties().Where(p => p.Name.Equals("PropertyName")).Any();
其他回答
我认为没有办法在不尝试访问动态变量的情况下发现动态变量是否有某个成员，除非你在c#编译器中重新实现动态绑定的处理方式。这可能包含很多猜测，因为根据c#规范，它是由实现定义的。
所以你应该尝试访问成员并捕获异常，如果它失败了:
dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame();
try
{
var x = myVariable.MyProperty;
// do stuff with x
}
catch (RuntimeBinderException)
{
// MyProperty doesn't exist
}
也许使用反射?
dynamic myVar = GetDataThatLooksVerySimilarButNotTheSame();
Type typeOfDynamic = myVar.GetType();
bool exist = typeOfDynamic.GetProperties().Where(p => p.Name.Equals("PropertyName")).Any();
在我的例子中，我需要检查具有特定名称的方法是否存在，因此我使用了一个接口
var plugin = this.pluginFinder.GetPluginIfInstalled<IPlugin>(pluginName) as dynamic;
if (plugin != null && plugin is ICustomPluginAction)
{
plugin.CustomPluginAction(action);
}
此外，接口可以包含的不仅仅是方法:
接口可以包含方法、属性、事件、索引器等等 这四种成员类型的组合。
来自:Interfaces (c#编程指南)
优雅，不需要陷阱异常或发挥反射…
The two common solutions to this include making the call and catching the RuntimeBinderException, using reflection to check for the call, or serialising to a text format and parsing from there. The problem with exceptions is that they are very slow, because when one is constructed, the current call stack is serialised. Serialising to JSON or something analogous incurs a similar penalty. This leaves us with reflection but it only works if the underlying object is actually a POCO with real members on it. If it's a dynamic wrapper around a dictionary, a COM object, or an external web service, then reflection won't help.
另一种解决方案是使用IDynamicMetaObjectProvider获取DLR看到的成员名。在下面的例子中，我使用一个静态类(Dynamic)来测试Age字段并显示它。
class Program
{
static void Main()
{
dynamic x = new ExpandoObject();
x.Name = "Damian Powell";
x.Age = "21 (probably)";
if (Dynamic.HasMember(x, "Age"))
{
Console.WriteLine("Age={0}", x.Age);
}
}
}
public static class Dynamic
{
public static bool HasMember(object dynObj, string memberName)
{
return GetMemberNames(dynObj).Contains(memberName);
}
public static IEnumerable<string> GetMemberNames(object dynObj)
{
var metaObjProvider = dynObj as IDynamicMetaObjectProvider;
if (null == metaObjProvider) throw new InvalidOperationException(
"The supplied object must be a dynamic object " +
"(i.e. it must implement IDynamicMetaObjectProvider)"
);
var metaObj = metaObjProvider.GetMetaObject(
Expression.Constant(metaObjProvider)
);
var memberNames = metaObj.GetDynamicMemberNames();
return memberNames;
}
}
Denis的回答让我想到了另一个使用JsonObjects的解决方案，
头属性检查器:
Predicate<object> hasHeader = jsonObject =>
((JObject)jsonObject).OfType<JProperty>()
.Any(prop => prop.Name == "header");
或许更好:
Predicate<object> hasHeader = jsonObject =>
((JObject)jsonObject).Property("header") != null;
例如:
dynamic json = JsonConvert.DeserializeObject(data);
string header = hasHeader(json) ? json.header : null;
