检查类中是否存在属性

我尝试知道一个类中是否存在一个属性，我尝试这样做:

public static bool HasProperty(this object obj, string propertyName)
{
return obj.GetType().GetProperty(propertyName) != null;
}

我不明白为什么第一个测试方法没有通过？

[TestMethod]
public void Test_HasProperty_True()
{
var res = typeof(MyClass).HasProperty("Label");
Assert.IsTrue(res);
}


[TestMethod]
public void Test_HasProperty_False()
{
var res = typeof(MyClass).HasProperty("Lab");
Assert.IsFalse(res);
}
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There are 2 possibilities.

You really don't have Label property.

You need to call appropriate GetProperty overload and pass the correct binding flags, e.g. BindingFlags.Public | BindingFlags.Instance

If your property is not public, you will need to use BindingFlags.NonPublic or some other combination of flags which fits your use case. Read the referenced API docs to find the details.

EDIT:

ooops, just noticed you call GetProperty on typeof(MyClass). typeof(MyClass) is Type which for sure has no Label property.

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最佳答案

Your method looks like this:

public static bool HasProperty(this object obj, string propertyName)
{
return obj.GetType().GetProperty(propertyName) != null;
}

This adds an extension onto object - the base class of everything. When you call this extension you're passing it a Type:

var res = typeof(MyClass).HasProperty("Label");

Your method expects an instance of a class, not a Type. Otherwise you're essentially doing

typeof(MyClass) - this gives an instanceof `System.Type`.

Then

type.GetType() - this gives `System.Type`
Getproperty('xxx') - whatever you provide as xxx is unlikely to be on `System.Type`

As @PeterRitchie correctly points out, at this point your code is looking for property Label on System.Type. That property does not exist.

The solution is either

a) Provide an instance of MyClass to the extension:

var myInstance = new MyClass()
myInstance.HasProperty("Label")

b) Put the extension on System.Type

public static bool HasProperty(this Type obj, string propertyName)
{
return obj.GetProperty(propertyName) != null;
}

and

typeof(MyClass).HasProperty("Label");
小开

This answers a different question:

If trying to figure out if an OBJECT (not class) has a property, 

OBJECT.GetType().GetProperty("PROPERTY") != null

returns true if (but not only if) the property exists.

In my case, I was in an ASP.NET MVC Partial View and wanted to render something if either the property did not exist, or the property (boolean) was true.

@if ((Model.GetType().GetProperty("AddTimeoffBlackouts") == null) ||
Model.AddTimeoffBlackouts)

helped me here.

Edit: Nowadays, it's probably smart to use the nameof operator instead of the stringified property name.

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If you are binding like I was:

<%# Container.DataItem.GetType().GetProperty("Property1") != null ? DataBinder.Eval(Container.DataItem, "Property1") : DataBinder.Eval(Container.DataItem, "Property2")  %>
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I got this error: "Type does not contain a definition for GetProperty" when tying the accepted answer.

This is what i ended up with:

using System.Reflection;


if (productModel.GetType().GetTypeInfo().GetDeclaredProperty(propertyName) != null)
{


}
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I'm unsure of the context on why this was needed, so this may not return enough information for you but this is what I was able to do:

if(typeof(ModelName).GetProperty("Name of Property") != null)
{
//whatevver you were wanting to do.
}

In my case I'm running through properties from a form submission and also have default values to use if the entry is left blank - so I needed to know if the there was a value to use - I prefixed all my default values in the model with Default so all I needed to do is check if there was a property that started with that.


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