C# Attributes, Reflection, Reading Attributes, and Analyzing Attributes Examples

Through reflection, after obtaining the property names and attributes, the next step is to retrieve the values of the properties.

        static void Main(string[] args)
        {
            Test test = new Test()
            {
                A = 13510377651,
                B = 1,
                C = 13510399648
            };
            Type type = test.GetType();

            // Get the list of properties in the class
            PropertyInfo[] properties = type.GetProperties();

            foreach (PropertyInfo item in properties)
            {
                MyAttribute att = (MyAttribute)Attribute.GetCustomAttribute(item, typeof(MyAttribute));
                if (att != null)
                {
                    Console.WriteLine(att.Name + "|" + item.Name + "|" + item.GetValue(test) + "|Is it a phone number: " + IsValid(item.PropertyType, item.GetValue(test)));
                }

            }
            Console.ReadKey();
        }

        private static bool IsValid(Type type, object value)
        {

            if (type != typeof(long))
                return false;

            long phone;
            bool num = long.TryParse(new ReadOnlySpan<char>(value.ToString().ToCharArray()), out phone);
            if (num == false)
                return false;

            if (phone < 100_000_000_00)
                return false;

            return true;
        }
    }
    public class Test
    {
        [My("1")]
        public long A { get; set; }
        [My("2")]
        public long B { get; set; }
        [My("3")]
        public long C { get; set; }
    }

    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Parameter,
         AllowMultiple = false)]
    public class MyAttribute : Attribute
    {
        public string Name { get; set; }
        public MyAttribute(string name)
        {
            Name = name;
        }
    }

Output:

1|A|13510377651|Is it a phone number: True
2|B|1|Is it a phone number: False
3|C|13510399648|Is it a phone number: True

An example of using reflection on a type is as follows:

// Usage:
// Access or modify the instance field myField
MyClass myObj = new MyClass() { myField = 1 }; // Create an instance
Type myType = typeof(MyClass); // Get the type, or myObj.GetType()
FieldInfo fieldInfo = myType.GetField("myField"); // Get the specified field info from the type
Console.WriteLine((int)fieldInfo.GetValue(myObj)); // 1, get the value of the instance field
fieldInfo.SetValue(myObj, 2); // Assign a value to the instance field
// Access or modify the static field myStaticField
FieldInfo staticFieldInfo = myType.GetField("myStaticField"); // Get the specified field info from the type
Console.WriteLine(staticFieldInfo.GetValue(null)); // 0, get the value of the static field
staticFieldInfo.SetValue(null, 2); // Assign a value to the static field

public class MyClass
{
    public int MyProperty { get; set; }
    public static int MyStaticProperty { get; set; }
}

// Usage:
// Access or modify the instance property MyProperty
MyClass myObj = new MyClass() { MyProperty = 1 }; // Create an instance
Type myType = typeof(MyClass); // Get the type, or myObj.GetType()
PropertyInfo propertyInfo = myType.GetProperty("MyProperty"); // Get the specified property info from the type
Console.WriteLine((int)propertyInfo.GetValue(myObj, null)); // 1, get the value of the instance property
propertyInfo.SetValue(myObj, 2, null); // Assign a value to the instance property

// Access or modify the static property MyStaticProperty
PropertyInfo staticPropertyInfo = myType.GetProperty("MyStaticProperty"); // Get the specified property info from the type
Console.WriteLine(staticPropertyInfo.GetValue(null, null)); // 0, get the value of the static property
staticPropertyInfo.SetValue(null, 2); // Assign a value to the static property

※ When using reflection to assign values to properties, an ArgumentException will be thrown if the property does not have a set accessor.