Is it possible to have a class with unknown amount or types of properties, that will restrict the property access if needed, in runtime.
For example, if we have the following class:
public class SomeClass
{
public string SomeProperty { get; set; }
}
Then, accessing the class property outcome will depend on some runtime state, that is controllable by classes that are aggregated to it in some way.
A possible solution, would be to add some public boolean variable that can be set, then determain the behaviour by it.
For example:
public class SomeClass
{
public bool CanAccess { get; set; }
private string _someProperty;
public string SomeProperty
{
get
{
if (CanAccess)
{
return _someProperty;
}
throw new Exception();
}
set
{
if (CanAccess)
{
_someProperty = value;
}
throw new Exception();
}
}
}
This solution however, will require the class implementor to:
Do it right
Do it for all properties
I am not sure it is possible, but I want to implement that class in some way that will eliminate the need to check this "CanAccess" feild for every property.
This further means that if in the future I add some more properties to that class, they will also comply that "CanAccess" state automatically.
Thanks for helping.
Related
I am making a save/load system for a big game project in C#.
Each class that has to be saved implements a method DoSnapshot().
Inside the method, the programmer must make a call to a function for every field in the class - either DoSnapshot(foo) if foo should be saved, or Ignore(foo) if it should not.
I have a DoSnapshot method for many primitive types like DoFloat, DoString as well as versions for complex types.
I have 100s of classes and the project is still being developed.
Is it possible to add some kind of verification that all of the fields in each class are either used in a Snapshot() or an Ignore() call? Omitting fields would cause bugs.
The verification could either be runtime, or compile-time. I only want to use it during development, it will not be released to users.
You could add an attribute to the fields that need to be saved, and then loop over every property in your class in the DoSnapshot method. When the property has the attribute you're looking for, you call Snapshot, otherwise you call Ignore.
public class SomeClass : SomeBaseClass
{
[Required]
public string Foo { get; set; }
public string Bar { get; set; }
public override void DoSnapshot()
{
var properties = this.GetType().GetProperties();
foreach (var property in properties)
{
var isRequired = property.GetCustomAttributes(typeof (RequiredAttribute), false).Length > 0;
if (isRequired)
{
// Something
}
else
{
// SomethingElse
}
}
}
}
What i would do is create an attribute and "tag" each field if it should be saved or not. Then, at runtime, i would query the class using reflection to get all fields which should be serialized:
public class RandomClass
{
public string Foo { get; set; }
[Ignore]
public int Bar { get; set; }
}
public class IgnoreAttribute : Attribute
{
}
class Program
{
static void Main(string[] args)
{
var properties = typeof(RandomClass).GetProperties()
.Where(prop => !prop.IsDefined(typeof(IgnoreAttribute), false));
// Serialize all values
}
}
When I define an interface that contains a write-only property:
public interface IModuleScreenData
{
string Name { set; }
}
and attempt to (naively) implement it explicitly with an intention for the property to also have a publicly available getter:
public class ModuleScreen : IModuleScreenData
{
string IModuleScreenData.Name { get; set; }
}
then I get the following error:
Error 'IModuleScreenData.Name.get' adds an accessor not found in
interface member 'IModuleScreenData.Name'
The error is more or less expected, however, after this alternative syntax:
public class ModuleScreen : IModuleScreenData
{
public string Name { get; IModuleScreenData.set; }
}
has failed to compile, I suppose that what I am trying to do is not really possible. Am I right, or is there some secret sauce syntax after all?
You can do this:
public class ModuleScreen : IModuleScreenData
{
string IModuleScreenData.Name
{
set { Name = value; }
}
public string Name { get; private set; }
}
On a side note, I generally wouldn't recommend set-only properties. A method may work better to express the intention.
You can't change the how the interface is implemented in the inheriting class. That is the whole point.. if you need to do something new with a property you could make a new property that references the inherited properties specific implementation. Interfaces are there so you can conform to a specified standard for object inheritance.
UPDATE:
On second thought.. you should be able to just do this.... this will compile fine:
public class ModuleScreen : IModuleScreenData
{
public string Name { get; set; }
}
I want to show MyProperty1 or MyProperty2 based on MyPropertySelected. How to use a conditional statement if or else based on MyPropertySelected? Thanks.
// [Browsable(true)
// ????? conditional statement IF ELSE in here..
// IF (MyPropertySelected) MyProperty1 will be show ELSE MyProperty2 will be show.
public bool MyPropertySelected { get; set; }
// [Browsable(true) or [Browsable(false) depending on MyPropertySelected condition.
public int MyProperty1 { get; set; }
// [Browsable(true) or [Browsable(false) depending on MyPropertySelected condition.
public int MyProperty2 { get; set; }
You're confusing apples with oranges.
Attributes are metadata and a property value acquires its value on run-time.
In other words: attribute is something that you'll access using reflection and those aren't tied to a particular object but to the type of the object (i.e. the class).
Another issue is that you want to add an attribute to a property based on a condition that can't work in compile-time.
Your MyPropertySelected won't get any value until its enclosing class gets instantiated - that's creating an object, for example: MyClass a = new MyClass()-, meaning that adding or not adding the attribute would never be a compile-time choice.
I want to be clear: you can't do what you want purely using attributes!
You can't conditionally apply attributes based on run-time values.
Finally, I suspect you want to make something Browsable based on a condition, like your own question says. You can't do that.
Ok ok, but what...?
You can workaround your situation with a different software design.
1)
First, create an interface that will have any of the properties that would be browsable or not. But don't apply the attribute [Browsable(bool)] to the interface properties.
2)
Create two classes that implements the previously created interface.
In the first class, implement the interface properties and put a [Browsable(true)] attribute on them. In the second class, do the same, but this time put a [Browsable(false)] on them.
3)
Some code that creates the instance of the object will be the one that will also decide which one will be instantiated.
That is, externalizing MyPropertySelected outside of both classes and performing the whole condition switch in the caller.
public interface IBrowsableProperties
{
int Property1 { get;set; }
int Property2 { get;set; }
}
public class A : IBrowsableProperties
{
[Browsable(true)]
public int Property1 { get;set; }
[Browsable(true)]
public int Property1 { get;set; }
}
public class B : IBrowsableProperties
{
[Browsable(false)]
public int Property1 { get;set; }
[Browsable(false)]
public int Property1 { get;set; }
}
// Somewhere in some method...
bool propertySelected = true;
IBrowsableProperties instance = null;
if(propertySelected)
{
instance = new A();
}
else
{
instance = new B();
}
// ... do stuff with your instance of IBrowsableProperties!
UPDATE
I've reviewed some of your question's comments and I've found you're working with PropertyGrid control.
Anyway, you can apply the concept in your case. PropertyGrid can be inherited. You can create both PropertyGrid1 and PropertyGrid2 derived classes that both implement the proposed interface!
You probably want an intermediary property like this:
class Foo
{
public bool MyPropertySelected
{
get;
set;
}
public readonly int MyProperty
{
get
{
return MyPropertySelected ? MyProperty1 : MyProperty2;
}
}
private int MyProperty1
{
get;
set;
}
private int MyProperty2
{
get;
set;
}
}
I'm trying to teach myself about OOP in C#, but I have a question about when to use base. I understand the general principles, but I'm not sure what's best in the example below. This simple test includes:
An interface with two string properties
An abstract class that implements this interface and adds a couple more string properties
Two classes that implement the abstract class. One uses base and the other doesn't, but they both produce the same output when the program is executed.
My question is: in this example, is one implementation more desirable than the other? I'm not really sure if there are any meaningful differences between TranslationStyleA and TranslationStyleB, or if it's just down to personal preference?
Many thanks for your time and thoughts!
using System;
namespace Test
{
interface ITranslation
{
string English { get; set; }
string French { get; set; }
}
public abstract class Translation : ITranslation
{
public virtual string English { get; set; }
public virtual string French { get; set; }
public string EnglishToFrench { get { return English + " is " + French + " in French"; } }
public string FrenchToEnglish { get { return French + " is " + English + " in English"; } }
public Translation(string e, string f)
{
English = e;
French = f;
}
}
public class TranslationStyleA : Translation
{
public override string English
{
get { return base.English; }
set { base.English = value; }
}
public override string French
{
get { return base.French; }
set { base.French = value; }
}
public TranslationStyleA(string e, string f) : base(e, f)
{
}
}
public class TranslationStyleB : Translation
{
private string english;
public override string English
{
get { return english; }
set { english = value; }
}
private string french;
public override string French
{
get { return french; }
set { french = value; }
}
public TranslationStyleB(string e, string f) : base(e, f)
{
this.English = e;
this.French = f;
}
}
class Program
{
static void Main(string[] args)
{
TranslationStyleA a = new TranslationStyleA("cheese", "fromage");
Console.WriteLine("Test A:");
Console.WriteLine(a.EnglishToFrench);
Console.WriteLine(a.FrenchToEnglish);
TranslationStyleB b = new TranslationStyleB("cheese", "fromage");
Console.WriteLine("Test B:");
Console.WriteLine(b.EnglishToFrench);
Console.WriteLine(b.FrenchToEnglish);
Console.ReadKey();
}
}
}
The first thing that you need to understand is what's going on when you have an automatic property:
public virtual string English { get; set; }
Behind the scenes, the compiler is generating a private field, and getting/setting that private field when you access the property. It is equivalent to this
private string _english;
public virtual string English { get { return _english; } set { _english = value; } }
except that you don't know the name of the private field, and so you cannot access it.
So in your TranslationStyleA class, you are not actually doing anything with the English property, because it just accesses the base class's property directly and doesn't change it's behavior.
// None of this is even needed- we are just delegating to the base class
public override string English
{
get { return base.English; }
set { base.English = value; }
}
Now in the TranslationStyleB class, you are actually changing the behavior of the property (albeit in a fairly useless way). Instead of storing the value for the English property in the base class's auto-implemented private variable, you are storing it in the private variable defined at the derived class level:
private string english;
public override string English
{
get { return english; }
set { english = value; }
}
Neither of these implementations does anything of course, and as implemented neither is needed, since the base class implements the properties perfectly fine itself. So my answer to your original question is that neither is preferred, given the code as you describe it.
Now, let's look at an example where your question is relevant. You only need to override them if you want to change their behavior, for instance.
// We don't want any leading or trailing whitespace, so we remove it here.
public override string English
{
get { return base.English; }
set { base.English = value.Trim(); }
}
We want to delegate to the base class here, because of why these were properties in the first place. Semantically, a property is the same as a field:
public String Foo;
public String Foo { get; set; } // <-- why bother with all this extra { get; set; } stuff?
The reason is that from the compiler's perspective, it is a breaking change in an interface to go from a property to a field. So if I change
public String Foo;
to
public String Foo { get; set; }
Then any code that depends on my code needs to be recompiled. However, if I change
public String Foo { get; set; }
to
private string _foo;
public String Foo { get { return _foo; } set { _foo = value.Trim(); } }
then dependent code still only sees the public property, and does not need recompilation (because the interface of my class has not changed).
If the base class here (Translation) were to change it's behavior for the property English thus:
private string _english;
public String English { get { return _english; } set { _english = value.ToUpper(); } }
the you would want to pick that up in your derived classes!
So considering that properties have behavior associated with them, you should always delegate to the parent class implementation unless that implementation has undesirable effects in your deriving class.
The first style is definitely preferable unless you have some good reason to pick the other one.
The automatically-implemented properties of Translation each add a field, and style B adds more rather than using the ones the compiler added. Style A reuses the one the compiler added, saving some storage.
Additionally, there's no need to override the superclass's properties if you're not going to change their functionality. You could even write another style like this:
public class TranslationStyleC : Translation {
public TranslationStyleC(string e, string f) : base(e, f) {
}
}
You don't really need to override any of the superclass properties to achieve the effect that you intend, since you don't enhance the superclass behavior in any way.
If you remove the abstract modifier from the base Translation, you don't need the subclasses anymore, since it will be functionally equivalent to both.
Now, as to when to use base; you should use it when you want to access functionality in the superclass that's been overridden in the subclass. base calls are always statically bound to the superclass method at compile time; even if the superclass method is virtual (as in your case). For a curious thing that can happen with base calls take a look here.
As mentioned before, style A reuses the fields already declared whereas style B declares new fields. Regarding your question about when to use base, the rule of thumb would be "whenever you would like to reuse logic/code defined in the parent class".
It does come down to how you intend to leverage your constructs.
As implemented, the overridden members on TranslationStyleA are a bit redundant as the consumer could just as easily access the base members without providing the overrides in the base derivation. In cases such as these I personally won't bother overriding the base members at all if doing so doesn't add any value to design.
The second implementation is common when you truly want to override the setting and accessing of base class members, for instance, if the setting of a base class member is the catalyst for initiating another operation then the overriden member on the derivation would be an appropriate place for that to occur.
I wanted to know what is a good option to solve this issue ,
I have a class that expose an enum : (this is just an example)
public class Foo
{
public State FooState { get; private set; }
public string SomeData { get; set; }
public Foo(State state)
{
FooState = state;
}
public Foo()
{
}
public enum State
{
None,
Bad,
Good
}
}
in one use of the class the user can adjust the state, and on the other he can't so the state is set on NONE and that good but i dont want the user to have the possibility of setting it to None. i Know that there isnt an internal enum field obviously, is there any way it can be done else, bare in mine that the Foo class cant be changed due to specification.
Clarification
The meaning of the class can not be change is that the design and purpose of the class can not change, not the class itself.
The state of the class is only in use when the c'tor get a value. i cant use two classes or use interface due to reflection use in the future. (i just cant use typeof)
I believe you can do this by providing two interfaces with different access level, implement them explicitly and instead of Foo type use one of the interfaces either for read-only or full access.
Since Foo can not be changed you can use Wrapper approach:
Foo foo = new Foo(State.Good);
FooWrapper fooWrapper = new FooWrapper(foo);
// would be read-write
(FooWrapper as IReaonlyState).State
// would be readonly
(FooWrapper as IWritableState).State
public interface IReadonlyState
{
State FooState { get; }
}
public interface IWritableState
{
State FooState { get; set; }
}
public class FooWrapper : IReadonlyState, IWritableState
{
Foo foo;
public FooWrapper(Foo foo)
{
this.foo = foo;
}
State IReadonlyState.FooState
{
get
{
return this.foo.FooState;
}
}
State IWritableState.FooState
{
get
{
return this.foo.FooState;
}
set
{
this.foo.FooState = value;
}
}
}
So, you want the consumer to be able to set both State=Bad and State=Good.
But if State==None you should be able to read, but not change it. Sounds like you need to implement the setter explicitly.