Given a PropertyInfo object, how can I check that the setter of the property is public?
Check what you get back from GetSetMethod:
MethodInfo setMethod = propInfo.GetSetMethod();
if (setMethod == null)
{
// The setter doesn't exist or isn't public.
}
Or, to put a different spin on Richard's answer:
if (propInfo.CanWrite && propInfo.GetSetMethod(/*nonPublic*/ true).IsPublic)
{
// The setter exists and is public.
}
Note that if all you want to do is set a property as long as it has a setter, you don't actually have to care whether the setter is public. You can just use it, public or private:
// This will give you the setter, whatever its accessibility,
// assuming it exists.
MethodInfo setter = propInfo.GetSetMethod(/*nonPublic*/ true);
if (setter != null)
{
// Just be aware that you're kind of being sneaky here.
setter.Invoke(target, new object[] { value });
}
.NET properties are really a wrapping shell around a get and set method.
You can use the GetSetMethod method on the PropertyInfo, returning the MethodInfo referring to the setter. You can do the same thing with GetGetMethod.
These methods will return null if the getter/setter is non-public.
The correct code here is:
bool IsPublic = propertyInfo.GetSetMethod() != null;
public class Program
{
class Foo
{
public string Bar { get; private set; }
}
static void Main(string[] args)
{
var prop = typeof(Foo).GetProperty("Bar");
if (prop != null)
{
// The property exists
var setter = prop.GetSetMethod(true);
if (setter != null)
{
// There's a setter
Console.WriteLine(setter.IsPublic);
}
}
}
}
You need to use the underling method to determine accessibility, using PropertyInfo.GetGetMethod() or PropertyInfo.GetSetMethod().
// Get a PropertyInfo instance...
var info = typeof(string).GetProperty ("Length");
// Then use the get method or the set method to determine accessibility
var isPublic = (info.GetGetMethod(true) ?? info.GetSetMethod(true)).IsPublic;
Note, however, that the getter & setter may have different accessibilities, e.g.:
class Demo {
public string Foo {/* public/* get; protected set; }
}
So you can't assume that the getter and the setter will have the same visibility.
Related
I am trying to find a way to take a class's property and pass it to a method along with another variable to update the property based on conditions. For example
The class
public class MyClass{
public string? Prop1 { get; set; }
public string? Prop2 { get; set; }
public bool? Prop3 { get; set; }
public DateTime? Prop4 { get; set; }
... etc...
}
Test code I would like to get to work...:
var obj = new MyClass();
MyCheckMethod(ref obj.Prop1, someCollection[0,1]);
in the method:
private void MyCheckMethod(ref Object obj, string value)
{
if (!string.isnullorempty(value))
{
// data conversion may be needed here depending on data type of the property
obj = value;
}
}
I want to be able to pass any property of any class and update the property only after validating the value passed in the method. I was hoping I could do this with generics, but I haven't yet found a way to do so. Or if I am over complicating what I need to do.
The problem is that there may be a bit more to the validation of the passed in value than just a simple isnullorempy check.
I also thought about doing something like this:
private void MyCheckMethod(ref object obj, Action action)
Then I could do something like this:
...
MyCheckMethod(ref obj.Prop1, (somecollection[0,1]) => {
... etc....
})
So I am looking for some guidance on how to proceed.
updated info:
The incoming data is all in string format (this is how a 3rd party vendor supplies the data). The data is supplied via API call for the 3rd party product... part of their SDK. However in my class I need to have proper data types. Convert string values to datetime for dates, string values to int for int data types, etc... . The other caveat is that if there isnt a valid value for the data type then the default value of the property should be NULL.
Additional Information:
The incoming data is always in string format.
eg:
I have to update a boolean property.
The incoming value is "". I test to see if the string Value isNullOrEmpty. It is so I dont do anything to property.
The next property datatype is decimal.
The incoming value is "0.343".
I Test to see if the string value is NullorEmpty. It isnt so I can update the property once I do a convert etc.....
Hope this helps.
Thanks
Full solution after edits:
public static class Extensions
{
//create other overloads
public static void MyCheckMethodDate<TObj>(this TObj obj,Expression<Func<TObj,DateTime>> property, string value)
{
obj.MyCheckMethod(property, value, DateTime.Parse);
}
public static void MyCheckMethod<TObj,TProp>(this TObj obj,Expression<Func<TObj,TProp>> property, string value,Func<string, TProp> converter)
{
if(string.IsNullOrEmpty(value))
return;
var propertyInfo = ((MemberExpression)property.Body).Member as PropertyInfo;
if(null != propertyInfo && propertyInfo.CanWrite)
{
propertyInfo.SetValue(obj, converter(value));
}
}
}
public class Obj
{
public object Prop1{get;set;}
public string Prop2{get;set;}
public DateTime Prop3{get;set;}
}
public class Program
{
public static void Main()
{
var obj = new Obj();
obj.MyCheckMethodDate(x=>x.Prop3, "2018-1-1");
Console.WriteLine(obj.Prop3);
}
}
You can pass a lambda expression:
void DoSomething<T>(Expression<Func<T>> property)
{
var propertyInfo = ((MemberExpression)property.Body).Member as PropertyInfo;
if (propertyInfo == null)
{
throw new ArgumentException("The lambda expression 'property' should point to a valid Property");
}else{
var name = ((MemberExpression)property.Body).Member.Name;
var value = property.Compile();
//Do whatever you need to do
}
}
To use:
DoSomething(() => obj.Property1);
You can't pass a reference to an arbitrary property. A property is basically implemented as two methods, set_Property and get_Property, and there's no way to bundle these together.
One option is to have your checker function take delegates to access the property. For example:
private void MyCheckMethod(Func<string> getter, Action<string> setter)
{
var value = getter();
var newValue = value.ToUpper();
setter(value);
}
So now you would say something like this:
public class MyClass
{
public string Prop1 { get; set; }
public string Prop2 { get; set; }
}
var c = new MyClass();
MyCheckMethod(() => c.Prop1, value => c.Prop1 = value);
Use reflection with compiled expressions.
This performs better than reflection and a little bit slower than native code.
It's not type safe, but you can add runtime validation.
I'm trying to find a way to get access to attributes which have been applied at the property level from within an object, but am hitting a brick wall. It appears that the data is stored at the type level, but I need it at the property level.
Here's an example of what I'm trying to make:
public class MyClass
{
[MyAttribute("This is the first")]
MyField First;
[MyAttribute("This is the second")]
MyField Second;
}
public class MyField
{
public string GetAttributeValue()
{
// Note that I do *not* know what property I'm in, but this
// should return 'this is the first' or 'this is the second',
// Depending on the instance of Myfield that we're in.
return this.MyCustomAttribute.value;
}
}
Attributes aren't used that way. Attributes are stored in the class object that contains the attribute, not the member object/field that is declared within the class.
Since you want this to be unique per member, it feels more like this should be member data with MyField, something passed in by the constructor.
If you're hell bent on using an attribute, you could add code in your constructor that used reflection on every member that has an attribute attached to it an attempts to set its instance data to what you want, but you would need to make sure that all your MyField objects are fully constructed.
Alternately you could make your setter look like this:
private MyField _first;
[MyAttribute("This is the first")]
public MyField First {
get { return _first; }
set {
_first = value;
if (_first != null) {
_first.SomeAttribute = GetMyAttributeValue("First");
}
}
}
private string GetMyAttributeValue(string propName)
{
PropertyInfo pi = this.GetType().GetPropertyInfo(propName);
if (pi == null) return null;
Object[] attrs = pi.GetCustomAttributes(typeof(MyAttribute));
MyAttribute attr = attrs.Length > 0 ? attrs[0] as MyAttribute : null;
return attr != null ? attr.Value : null;
}
I know the name of a property in my C# class. Is it possible to use reflection to set the value of this property?
For example, say I know the name of a property is string propertyName = "first_name";. And there actaully exists a property called first_name. Can I set it using this string?
Yes, you can use reflection - just fetch it with Type.GetProperty (specifying binding flags if necessary), then call SetValue appropriately. Sample:
using System;
class Person
{
public string Name { get; set; }
}
class Test
{
static void Main(string[] arg)
{
Person p = new Person();
var property = typeof(Person).GetProperty("Name");
property.SetValue(p, "Jon", null);
Console.WriteLine(p.Name); // Jon
}
}
If it's not a public property, you'll need to specify BindingFlags.NonPublic | BindingFlags.Instance in the GetProperty call.
This is my code where I create a "copy" of one object (Entity) into a custom object.
It copies just properties with the same name in both source and target.
My problem is when an Entity has a navgiaton to another Entity, for this case I added a custom attribute that I add above the property in the custom class.
For example the custom class looks like:
public class CourseModel:BaseDataItemModel
{
public int CourseNumber { get; set; }
public string Name { get; set; }
LecturerModel lecturer;
[PropertySubEntity]
public LecturerModel Lecturer
{
get { return lecturer; }
set { lecturer = value; }
}
public CourseModel()
{
lecturer = new LecturerModel();
}
}
The problem is in targetProp.CopyPropertiesFrom(sourceProp); line, when I try to call extension method again (to copy the nested object) ,because the type is determined on run time, extension method couldn't resolved on compile time.
Maybe I am missing something...
public static void CopyPropertiesFrom(this BaseDataItemModel targetObject, object source)
{
PropertyInfo[] allProporties = source.GetType().GetProperties();
PropertyInfo targetProperty;
foreach (PropertyInfo fromProp in allProporties)
{
targetProperty = targetObject.GetType().GetProperty(fromProp.Name);
if (targetProperty == null) continue;
if (!targetProperty.CanWrite) continue;
//check if property in target class marked with SkipProperty Attribute
if (targetProperty.GetCustomAttributes(typeof(SkipPropertyAttribute), true).Length != 0) continue;
if (targetProperty.GetCustomAttributes(typeof(PropertySubEntity), true).Length != 0)
{
//Type pType = targetProperty.PropertyType;
var targetProp = targetProperty.GetValue(targetObject, null);
var sourceProp = fromProp.GetValue(source, null);
targetProp.CopyPropertiesFrom(sourceProp); // <== PROBLEM HERE
//targetProperty.SetValue(targetObject, sourceEntity, null);
}
else
targetProperty.SetValue(targetObject, fromProp.GetValue(source, null), null);
}
}
You'll have to cast first.
((BaseDataItemModel)targetProp).CopyPropertiesFrom(sourceProp);
Either you need to cast targetProperty to BaseDataItemModel so you can call the extension method on it (edit: as in agent-j's answer), or otherwise you could just forget about that base class. Why does your reflection algorithm need it? It could work on any class, and is directed purely by the attributes on properties.
And if it works on any object, it shouldn't be an extension method.
What is the easiest way to take an objects and convert any of its values from null to string.empty ?
I was thinking about a routine that I can pass in any object, but I am not sure how to loop through all the values.
When your object exposes it's values via properties you can write something like:
string Value { get { return m_Value ?? string.Empty; } }
Another solution is to use reflection. This code will check properties of type string:
var myObject = new MyObject();
foreach( var propertyInfo in myObject.GetType().GetProperties() )
{
if(propertyInfo.PropertyType == typeof(string))
{
if( propertyInfo.GetValue( myObject, null ) == null )
{
propertyInfo.SetValue( myObject, string.Empty, null );
}
}
}
Using reflection, you could something similar to :
public static class Extensions
{
public static void Awesome<T>(this T myObject) where T : class
{
PropertyInfo[] properties = typeof(T).GetProperties();
foreach(var info in properties)
{
// if a string and null, set to String.Empty
if(info.PropertyType == typeof(string) &&
info.GetValue(myObject, null) == null)
{
info.SetValue(myObject, String.Empty, null);
}
}
}
}
Presumably, you have a report or a form somewhere showing "null" all over the place, instead of a nice, pleasant "".
It's best to leave the nulls as they are, and modify your display code wherever appropriate. Thus, a line like this:
label1.Text = someObject.ToString();
should become:
if (someObject == null)
{
label1.Text = ""; // or String.Empty, if you're one of *those* people
}
else
{
label1.Text = someObject.ToString();
}
and you can functionalize it as necessary:
public void DisplayObject(Label label, Object someObject)
{
if (someObject == null)
{
label.Text = ""; // or String.Empty, if you're one of *those* people
}
else
{
label.Text = someObject.ToString();
}
}
You could use reflection. Here's an example with one level of nesting:
class Foo
{
public string Prop1 { get; set; }
public string Prop2 { get; set; }
public string Prop3 { get; set; }
}
class Program
{
static void Main(string[] args)
{
var foo = new Foo
{
Prop1 = (string)null,
Prop2 = (string)null,
Prop3 = (string)null,
};
var props = typeof(Foo).GetProperties()
.Where(x => x.PropertyType == typeof(string));
foreach (var p in props)
{
p.SetValue(foo, string.Empty, null);
}
}
}
You can do that via reflection without too much trouble, and I am sure that by the time I post this there will be answers that tell you exactly how to do that.
But I personally don't like the reflection option.
I prefer to maintain object invariants for all of the object's members through a variety of means. For string members, the invariant is often that it not be null, and sometimes there are maximum length requirements as well (for storage in a database, for example). Other members have other sorts of invariants.
The first step is to create a method that checks all the invariants that you define for the object.
[Conditional("DEBUG")]
private void CheckObjectInvariant()
{
Debug.Assert(name != null);
Debug.Assert(name.Length <= nameMaxLength);
...
}
Then you call this after any method that manipulates the object in any way. Since it is decorated with the ConditionalAttribute, none of these calls will appear in the release version of the application.
Then you just have to make sure that none of the code allows any violations of these invariants. This means that the string fields need to have either initializers in their declarations or they need to be set in all the constructors for the object.
A special problem, and the one that probably motivated this question, is what to do about automatic properties.
public string Name { get; set; }
Obviously, this can be set to null at any time, and there's nothing you can do about that.
There are two options with regard to automatic properties. First, you can just not use them at all. This avoids the problem entirely. Second, you can just allow any possible string value. That is, any code that uses that property has to expect nulls, 10 mb strings or anything in between.
Even if you go with the reflection option to remove nulls, you still have to know when to call the magic-null-removal method on the object to avoid NullReferenceExceptions, so you haven't really bought anything that way.
+1 to Tanascius's answer. I used this answer but tweaked it a bit.
First I only grab the properties that are strings, so it doesn't loop through all my properties. Secondly, I placed in it my BaseEntity class that all my entities inherit from, which makes it global, so I don't have to put it on all my Entities.
public class BaseEntity
{
public int Id { get; set; }
public BaseEntity()
{
var stringProperties = this.GetType().GetProperties().Where(x => x.PropertyType == typeof(string));
foreach (var property in stringProperties)
{
if (property.GetValue(this, null) == null)
{
property.SetValue(this, string.Empty, null);
}
}
}
}