This is easier to explain with an example. Given these two classes:
public class MyClassA
{
public String Property_A { get; set; }
public String Property_B { get; set; }
public String Property_C { get; set; }
public String Property_D { get; set; }
...
public String Property_Y { get; set; }
}
public class MyClassB: MyClassA
{
public String Property_Z { get; set; }
}
Suppose I have fully created instance of MyClassA (with all properties from A - Y filled in). Then I need to make an instance of MyClassB which is exactly the same as my instance of MyClassA but with Property_Z filled in (with a custom value of course). How can I do this?
Doing this does not work (throws and Invalid Cast Exception):
MyClassB myInstanceB = (myClassB) myInstanceA;
myInstance.Property_Z = myCustomValue;
I have not needed to do anything like this since my C++ days and I am stumped.
Any ideas?
UPDATE: I found a solution to my problem in how I create the instances. It is below. I did not mark it as the answer because it did not exactly fit my question.
The instance you've created is a MyClassA. That is its runtime type, not MyClassB. You cannot cast a MyClassA instance to a MyClassB at runtime because MyClassB is a more specific type than MyClassA.
You need to create a brand-new instance of MyClassB. One way to clean this up is to create a constructor that takes a MyClassA, e.g.
public class MyClassB : MyClassA
{
public MyClassB(MyClassA a, string z)
{
this.PropertyA = a.PropertyA;
this.PropertyB = a.PropertyB;
// etc.
this.PropertyZ = z;
}
public string PropertyZ { get; set; }
}
You can use Reflection to copy base class properties as shown here.
public void Update(MyObject o)
{
MyObject copyObject = ...
Type type = o.GetType();
while (type != null)
{
UpdateForType(type, o, copyObject);
type = type.BaseType;
}
}
private static void UpdateForType(Type type, MyObject source, MyObject destination)
{
FieldInfo[] myObjectFields = type.GetFields(
BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
foreach (FieldInfo fi in myObjectFields)
{
fi.SetValue(destination, fi.GetValue(source));
}
}
The straightforward answer:
public class MyClassA
{
public String Property_A { get; set; }
public String Property_B { get; set; }
public String Property_C { get; set; }
public String Property_D { get; set; }
...
public String Property_Y { get; set; }
}
public class MyClassB: MyClassA
{
public MyClassB(MyClassA copy)
{
Property_A = copy.PropertyA;
Property_B = copy.PropertyB;
...
}
public String Property_Z { get; set; }
}
Use it like this:
MyClassB o = new MyClassB(instanceOfMyClassA);
o.Property_Z = whatever;
Sounds like you're looking for a free copy constructor. C# doesn't supply one (http://msdn.microsoft.com/en-us/library/ms173116%28VS.80%29.aspx) but you can do it pretty easily with Object.MemberwiseClone or the BinaryFormatter serializer (http://www.codeproject.com/KB/tips/SerializedObjectCloner.aspx). Take care to know if you want a shallow copy or deep copy.
You could define an explicit or implicit cast from MyClassA to MyClassB and use the syntax you've provided.
public class MyClassB : MyClassA
{
public String Property_Z { get; set; }
public static explicit operator MyClassB(MyClassA a)
{
MyClassB b = new MyClassB();
b.Property_A = a.Property_A;
/* ... */
b.Property_Y = a.Property_Y;
return b;
}
}
What about:
Create a base class that implements IClonable and has all the string properties A to D, and Z.
Create instance of this class for MyClassA.
Create instance of MyClassB by cloning MyClassA.
Set property Z in MyClassB.
Here is what I ended up doing:
I made my method that creates and sets up all the properties (A-Y) that uses type parameters. It looks like this:
public T MakeAMyClass<T>(AnotherClass
where T: MyClassA : new()
{
T returnValue = new T();
T.Property_A = somethingToSetFrom.MakeAPropertyA();
// Fill in the rest of the properties
}
Because a type parameter can be a type that is descended from the constraint, I am able to pass in MyClassB objects and get them made the same way as myClassA.
Then I can make either one as needed.
MyClassA myInstanceA = MakeAMyClass<MyClassA>(somethingToSetFrom);
MyClassB myInstanceB = MakeAMyClass<MyClassB>(somethingToSetFrom);
myInstanceB.Property_Z = someotherValue;
The lets me avoid having to make a method to copy all the properties from MyClassA to MyClassB.
Related
Is there a way to copy an object fields to a base class in a derived class constructor without having to individually copying every field?
Example:
public class A
{
int prop1 { get; set; }
int prop2 { get; set; }
}
public class B : A
{
public B(A a)
{
//base = a; doesn't work.
base.prop1 = a.prop1;
base.prop2 = a.prop2;
}
}
A a = new A();
B b = new B(a);
public class A
{
public A(A a)
{
prop1 = a.prop1;
prop2 = a.prop2;
}
int prop1 { get; set; }
int prop2 { get; set; }
}
public class B : A
{
public B(A a) : base (a)
{
}
}
A a = new A();
B b = new B(a);
Something like this, although I'm not sure if it is syntactically correct because I didn't compile it. You should use the base keyword after the child class's constructor to pass the values of it's dependencies to the base class.
Edit: But I just realized that you are passing a base class to a child class. And this is a design flaw.
It sounds like you want to add all properties from A to B without having to specify them all separately. If you don't want to have to keep adding new ones to the constructor, you could use reflection to do the work for you.
public B(A a)
{
var bType = this.GetType();
// specify that we're only interested in public properties
var aProps = a.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);
// iterate through all the public properties in A
foreach (var prop in aProps)
{
// for each A property, set the same B property to its value
bType.GetProperty(prop.Name).SetValue(this, prop.GetValue(a));
}
}
A few notes about this:
The above code sets public instance properties, so you'd need to change your properties in A to be public.
I'd only consider this safe because you know that B contains everything in A (since it is derived from it).
If you only have a few properties, especially if they don't change often, just list them individually... it'll be easier to see exactly what your code is doing.
I can't for the life of me understand why you want to do this
You are passing an instance of Base class into the constructor of a derived class. What are you trying to do?
have you tried this = a instead of base = a?
The members are private, so you can't access them from even a derived class. Even if they were protected, you still couldn't access them on an instance of A from the B class.
In order to do this without reflection, the members will have to be public:
public class A
{
public int prop1 { get; set; }
public int prop2 { get; set; }
}
// Define other methods and classes here
public class B : A
{
public B(A a)
{
//base = a; doesn't work.
base.prop1 = a.prop1;
base.prop2 = a.prop2;
}
}
If you really want to do this and cannot access the properties via inheritance then you can do via reflection like this:
public class Aclass
{
public int Prop1 { get; set; }
public int Prop2 { get; set; }
}
public class Bclass : Aclass
{
public Bclass(Aclass aInstance)
{
CopyPropertiesFromAltInstance(aInstance);
}
public void CopyPropertiesFromAltInstance(Aclass aInstance)
{
PropertyInfo[] aProperties = aInstance.GetType().GetProperties();
PropertyInfo[] myProperties = this.GetType().GetProperties();
foreach (PropertyInfo aProperty in aProperties)
{
foreach (PropertyInfo myProperty in myProperties)
{
if (myProperty.Name == aProperty.Name && myProperty.PropertyType == aProperty.PropertyType)
{
myProperty.SetValue(this, aProperty.GetValue(aInstance));
}
}
}
}
}
I'm having some interface woes!
Here's the code:
I expected to be able to access the properties Added and ID through my test template, but intellisense says No!
Am I misusing an interface? Have I made a silly error?
Any advice appreciated - this is driving me nuts.
namespace blah.blah.blah
{
public interface ITrackedItem
{
DateTime Added { get; set; }
int ID { get; set; }
}
public class TestTemplate<ITrackedItem>
where ITrackedItem : new()
{
public SortedSet<ITrackedItem> Set { get; set; }
public void Test()
{
Set = new SortedSet<ITrackedItem>();
foreach (var item in Set)
{
// cannot access any properties here
// var ID = item.ID; <=============|
}
}
}
}
This is the problem:
public class TestTemplate<ITrackedItem>
You've declared a type parameter called ITrackedItem, which is entirely different to the ITrackedItem interface. It's not clear that your type needs to be generic at all - can you not just use
public class TestTemplate
? If you want it to be generic in a type which must implement ITrackedItem, you should use something like:
public class TestTemplate<T>
where T : ITrackedItem, new()
{
public SortedSet<T> Set { get; set; }
public void Test()
{
Set = new SortedSet<T>();
foreach (var item in Set)
{
// now you can access any properties here
//
}
}
}
Is there an easy way to copy everything from a strongly typed object into a dynamic one? The target has to be a DynamicObject as determined by a 3rd party library I'm using. Everything from TypedModel needs to go into MyDynamicObject at runtime.
public class MyDynamicObject : DynamicThirdPartyObject
{ }
public class TypedModel
{
public string text { get; set; }
public int number { get; set; }
public List<SomeOtherModel> someList { get; set; }
}
Existing solutions I found on SO all match up properties between typed classes.
EDIT
Found a simple solution based on FastMember:
public void CopyProperties(object source, DynamicObject target)
{
var wrapped = ObjectAccessor.Create(target);
foreach (var prop in source.GetType().GetProperties())
{
wrapped[prop.Name] = prop.GetValue(source);
}
}
I propoes to use reflection.
suppose you make following declaration:
public class MyDynamicObject : DynamicThirdPartyObject
{ }
public class TypedModel
{
public string text { get; set; }
public int number { get; set; }
public List<SomeOtherModel> ListOtherModel { get; set; }
}
Lets say you want to get properties of instance:
typedModel.GetType().GetProperties();
Another possible situation is if you want to copy type:
typeof(TypedModel).GetProperties();
TypedModel typeModel = new TypedModel {number = 1, text = "text1",
ListOhterModel = new List()
};
foreach(var prop in typeModel.GetType().GetProperties())
{
Console.WriteLine("{0}={1}", prop.Name, prop.GetValue(typeModel, null));
}
And if you need to go through hierarchy, maybe you need to use recursion, in order to go through nested types, I mean you can use reflection for copying all members of SomeOtherModel.
I have the following class:
class Foo
{
public Foo()
{
Console.WriteLine("Foo");
}
public string A { get; set; } = GetStr("A");
public string B { get; set; } = GetStr("B");
public static string GetStr(string str)
{
Console.WriteLine(str);
return str;
}
}
when I create an instance from it, the output is this:
A
B
Foo
if I change the of my properties to:
public string B { get; set; } = GetStr("B");
public string A { get; set; } = GetStr("A");
the output is:
B
A
Foo
My Question is:
Does order of properties in a class important and may effect my program?
Note: I use C# 6.0 new feature: Property initializer More
Field (and property, since C# 6) initializers are run first, in the order in which they are declared, then the constructor is executed.
So yes, the order of the properties affects the order in which they will be initialized; but the constructor will always be executed last.
In my experience (in C#), when using reflection, the order of the fields is returned as they are listed in the class (so it may be important).
For example:
public class TestClass
{
// purposely not in alphabetical order and of different types.
public string C { get; set; }
public int A { get; set; }
public string B { get; set; }
}
and then create an instance and assign values:
TestClass testObject = new TestClass();
// purposely not in same order as in class
testObject.B = "1";
testObject.C = "2";
testObject.A = 3;
and finally loop through properties:
foreach (PropertyInfo prop in typeof(TestClass).GetProperties())
{
Console.WriteLine("{0} = {1}", prop.Name, prop.GetValue(testObject, null));
}
prints out the following:
C = 2
A = 3
B = 1
The result is the same order as in the class definition.
Order of properties doesn't matter. Your constructor call the GetStr method which writes the string in console. Because of that order of properties seem change.
Say we have a simple class model with classes as feilds (inside compiled, not modifiable Dll):
public class SubSubClassTest {
public int Data { get; set; }
}
public class SubClassTest {
public string InnerStr { get; set; }
public int InnerInteger { get; set; }
public SubSubClassTest InnerLoad { get; set; }
public SubClassTest() {
InnerLoad = new SubSubClassTest();
}
}
public class Test {
public string Str { get; set; }
public int Integer { get; set; }
public SubClassTest Load { get; set; }
public Test() {
Load = new SubClassTest();
}
}
And we want to edit it using PropertyGrid.
public partial class ApplicationForm : Form {
public ApplicationForm() {
InitializeComponent();
var test = new Test();
propertyGrid.SelectedObject = test;
}
}
And I do not have abilety to change classes (as I get them from Dll) and they have no [TypeConverter(typeof(ExpandableObjectConverter))] attribute on all members that are classes I get sush picture:
And members that are from my namespace class type are not editable.
If all such members havd [TypeConverter(typeof(ExpandableObjectConverter))] attribute I would have another picture and all would be fine:
I wonder how to make PropertyGrid use PropertyGrid for all nested classes?
You could try changing the TypeConverterAttribute value using PropertyDescriptor and Reflection. I wouldn't recommend to do this but to show that its possible I have added the sample code. I verified with your example and it works. But I cannot assure that it would work in all scenarios. Food for thought...
var test = new Test();
SetTypeConverterAttribute(test);
propertyGrid.SelectedObject = test;
private void SetTypeConverterAttribute(Test test)
{
foreach (PropertyDescriptor item in TypeDescriptor.GetProperties(test))
{
TypeConverterAttribute attribute = item.Attributes[typeof(TypeConverterAttribute)] as TypeConverterAttribute;
if (attribute != null && item.PropertyType == typeof(SubClassTest))
{
FieldInfo field = attribute.GetType().GetField("typeName", BindingFlags.NonPublic | BindingFlags.Instance);
if (field != null)
{
field.SetValue(attribute, typeof(ExpandableObjectConverter).FullName);
}
}
}
}
If you have control over the classes, you can create a common base class and decorate this base class with the TypeConverterAttribute. In that case, any property that will reference any instance of this type will use the ExpandableObjectConverter, unless this behavior is overridden by the property (using another TypeConverterAttribute).