At runtime, how can I test whether a Property is readonly?

Question

I am auto-generating code that creates a winform dialog based on configuration (textboxes, dateTimePickers etc). The controls on these dialogs are populated from a saved dataset and

needs to Set and Get properties for various control objects (custom or other).

//Upon opening of form - populate control properties with saved values
MyObject.Value = DataSource.GetValue("Value");

//Upon closing of form, save values of control properties to dataset.
DataSource.SetValue("Value") = MyObject.Value;

Now this is all fine, but what of readOnly properties? I wish to save the result of the property but need to know when to NOT generate code that will attempt to populate it.

//Open form, attempt to populate control properties.
//Code that will result in 'cannot be assigned to -- it is read only'
MyObject.HasValue = DataSource.GetValue("HasValue");
MyObject.DerivedValue = DataSource.GetValue("Total_SC2_1v1_Wins");

//Closing of form, save values. 
DataSource.SetValue("HasValue") = MyObject.HasValue;

Remember that I do not know the type of object I've instantiate until runtime.

How can I (at runtime) identify a readonly property?

Answer 1

With PropertyDescriptor , check IsReadOnly .

With PropertyInfo , check CanWrite (and CanRead , for that matter).

You may also want to check [ReadOnly(true)] in the case of PropertyInfo (but this is already handled with PropertyDescriptor ):

 ReadOnlyAttribute attrib = Attribute.GetCustomAttribute(prop,
       typeof(ReadOnlyAttribute)) as ReadOnlyAttribute;
 bool ro = !prop.CanWrite || (attrib != null && attrib.IsReadOnly);

IMO, PropertyDescriptor is a better model to use here; it will allow custom models.

Answer 2

I noticed that when using PropertyInfo, the CanWrite property is true even if the setter is private. This simple check worked for me:

bool IsReadOnly = prop.SetMethod == null || !prop.SetMethod.IsPublic;

Answer 3

Also - See Microsoft Page

using System.ComponentModel;

// Get the attributes for the property.

AttributeCollection attributes = 
   TypeDescriptor.GetProperties(this)["MyProperty"].Attributes;

// Check to see whether the value of the ReadOnlyAttribute is Yes.
if(attributes[typeof(ReadOnlyAttribute)].Equals(ReadOnlyAttribute.Yes)) {
   // Insert code here.
}

Answer 4

I needed to use this for different classes, so I created this generic function:

public static bool IsPropertyReadOnly<T>(string PropertyName)
{
    MemberInfo info = typeof(T).GetMember(PropertyName)[0];

    ReadOnlyAttribute attribute = Attribute.GetCustomAttribute(info, typeof(ReadOnlyAttribute)) as ReadOnlyAttribute;

    return (attribute != null && attribute.IsReadOnly);
}