CHECK IF A PROPERTY EXIST IN A CLASS

ben reitman

Total Post:96

Points:676
Posted by  ben reitman
C# 
C#
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Hi Expert!

I try to know if a property exist in a class, I tried this :

public static bool HasProperty(this object obj, string propertyName)
{
    return obj.GetType().GetProperty(propertyName) != null;
}
I don't understand why the first test method does not pass ?

[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);
}

Thanks in advance!

  1. AVADHESH PATEL

    Post:604

    Points:4228
    Re: Check if a property exist in a class

    Hi Ben!

    Your method looks as following!

    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");

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