Hi is it possible to specify a method that is the default method for a C# class? I am writing a short class to output embed code for a video, here is the basic idea:
public class EmbeddedVideo
{
public string VideoPath { get; set; }
public string ImagePath { get; set; }
public string EmbedCode()
{
return "...";
}
}
Now if I were to say:
Response.Write(new EmbeddedVideo());
It would output the result of the GetType() method. How can I specify that I would like the EmbedCode() method to be the default in this context?
Override ToString(), which gets called in many scenarios where string conversion takes place:
public override string ToString()
{
return EmbedCode();
}
The "default" you're referring to is the default implementation of Object.ToString(), which simply happens to return the type name:
The default implementation returns the fully qualified name of the type of the Object.
It sounds like by "default method" you mean "method which controls how instances of the type are displayed in methods like Write." If so what you want to do is override the ToString method.
public override string ToString() {
return EmbedCode();
}
Related
I'm building a parser for some data that's given as XML, something similar to:
Get file in path %windir%\system32\calc.exe and retrieve it's CreationTime
The small problem that I have is that the type of object that I'm retrieving (FileInfo in example above) and the data type of the property I'm reading (CreationTime which is DateTime in example above) isn't always the same.
For example: on a FileInfo object alone I could be asked for:
bool Exists
DateTime CreationTime
DateTime LastWriteTime
long Size
Version Version
Other object types could be things like FolderInfo, RegistryKey and RegistryValue
With that in mind, I created the following code:
public interface IPropertyRetriever<out T>
{
public string Name { get; }
public Property Property { get; }
public T RetrieveProperty();
}
public enum Property
{
Count,
DateCreated,
DateModified,
RegistryKeyExists,
RegistryValueExists,
Size,
Value,
Version
}
public class FilePropertyRetriever<T> : IPropertyRetriever<T>
{
public FilePropertyRetriever(string name, Property property, string path, bool is64Bit)
{
Name = name;
Property = property;
Path = path;
Is64Bit = is64Bit;
}
public string Name { get; }
public Property Property { get; }
public string Path { get; }
public T RetrieveProperty()
{
var file = ...
// Do something to retrieve FileInfo,
// assumes if it got to code below FileInfo.Exists is true
return (T) (object) (Property switch
{
Property.Count => file.Exists,
Property.DateCreated => file.CreationTime,
Property.DateModified => file.LastWriteTime,
Property.Size => file.Length,
Property.Version => Version.TryParse(FileVersionInfo.GetVersionInfo(Path).ProductVersion,
out var version)
? version
: null
});
}
}
I know that my T RetrieverProperty() method isn't exactly very good programming - I'm telling my method what type I want it to return when in fact it knows already and using generics to cast to the correct type (and boxing it first if DateTime/long/int), but I really can't think of a better way of doing this.
Any suggestions on how to improve this?
PS: The reason why the RetrieveProperty() accepts no parameters and instead uses properties is because the device where the object is created and where the method are run is not the same, the object is serialised and sent over.
why can't IPropertyRetriever just be this:
public interface IPropertyRetriever
{
public string Name { get; }
public int Count {get;}
public DateTime DateCreated {get;}
public DateTime DateModified {get;}
public bool RegistryKeyExists {get;}
public bool RegistryValueExists {get;}
public long Size {get;}
//etc
}
And call it something different IFileInformation. Or have different interfaces returned for different objects with a base interface as not all the above properties are relevant to all objects.
How can I get the name of the original property name which is passed as a parameter to a method?
class TestA
{
public string Foo { get; set; }
public TestA()
{
Foo = "Bar";
TestB.RegisterString(Foo);
}
}
class TestB
{
public static void RegisterString(string inputString)
{
// Here I want to receive the property name that was used
// to assign the parameter input string
// I want to get the property name "Foo"
}
}
You can add an argument with the nameof keyword. Not sure why you would want that anyway:
TestB.RegisterString(Foo, nameof(Foo));
This will pass in "Foo" as the second argument. There is no way to automate this, so you don't need to call nameof yourself, which makes doing this quite useless.
If you would call this from the Foo property, you could use the CallerMemberNameAttribute, which will put in the caller's name. The compiler will set the correct value, so you don't have to supply this yourself in the calling method.
public static void RegisterString( string inputString
, [CallerMemberName] string caller = null
)
{
// use caller here
}
That makes more sense to me.
I've a working WCF service and while writing a test for it, I added the following lines.
MyServiceClient client = new MyServiceClient();
Thing thing = client.GetThing();
System.WriteLine(thing.SomeProperty);
The above works just as supposed to. Then, I was trying to perform stringification and each of the following failed in a number of ways. The first fail is on these calls.
System.WriteLine(thing);
System.WriteLine("" + thing);
System.WriteLine(thing.ToString());
It only shows the name of the class, although I've added custom ToString method to Thing class. I haven't exposed the custom ToString explicitly but it's included in the classes created for me by VS automatically, so I'm assuming that it's exposed by the parent class (i.e. Object).
public class Thing
{
public String SomeProperty { ... }
public override String ToString() { ... }
//public new String ToString() { ... }
//public String ToString() { ... }
}
What am I missing here?
Then, I though that I could implement a new property, that returns the stringification instead. However, the property, although visible when I obtain the instance of Thing, is null.
public Stringification { get { return SomeProperty + "!"; } set { } }
//public ToString { get { return SomeProperty + "!"; } set { } }
Why isn't it providing me with the actual value of the property?
I am following the Preamble: what is a reference type? where it explains parameters passing as value or reference type. The first example has the following code:
using System;
using System.Text;
public class Example1
{
public static void Main (string[] args)
{
StringBuilder first = new StringBuilder();
StringBuilder second = first;
first.Append ("hello");
first = null;
Console.WriteLine (second);
}
}
And it does not provide the source code for the class (or struct) of StringBuilder, and I do not know how the Console.WriteLine(second) is able to return a string value just by using the identifier. Is it possible to return a value in the constructor?
I tried to write the class or struct by following (and it doesn't work):
struct StringBuilder
{
private string _myString;
public string StringBuilder
{
get { return _myString; }
set { _myString = value; }
}
public void Append(string str)
{
_myString = str;
}
}
Have a look a the documentation for Console.WriteLine(object value). It says this:
the ToString method of value is called to produce its string
representation, and the resulting string is written to the standard
output stream.
So (as others have written), if you want to print a string representation of your own class or struct, you should override the ToString() method.
StringBuilder is .net class in System.Text namespace.
Override ToString method for objects string representation.
public override string ToString()
{
return _myString;
}
Or print out your property:
Console.WriteLine (second.StringBuilder);
StringBuilder is a class, not a struct. C# is not like C++ in this respect: the two are in fact different. And Console.WriteLine(x) where x is an arbitrary class ends up as Console.WriteLine(x.ToString()).
What the code does is to call ToString on the StringBuilder instance. The code gets clearer if you explicitly call ToString instead of letting it be called implicitly:
Console.WriteLine(second.ToString());
You can override the ToString method in your own class. You should use classes, by the way, only use structs if you have a specific need for it. Structs are more complicated to implement correctly.
Example:
class Example {
public string Value { get; set; }
public Example(string value) {
Value = value;
}
public override string ToString() {
return Value;
}
}
Now the string value of your object will be its value:
Example ex = new Example("test");
Console.WriteLine(ex);
I have a class that stores a serialized value and a type. I want to have a property/method returning the value already casted:
public String Value { get; set; }
public Type TheType { get; set; }
public typeof(TheType) CastedValue { get { return Convert.ChangeType(Value, typeof(_Type)); }
Is this possible in C#?
It's possible if the class containing the property is generic, and you declare the property using the generic parameter:
class Foo<TValue> {
public string Value { get; set; }
public TValue TypedValue {
get {
return (TValue)Convert.ChangeType(Value, typeof(TValue));
}
}
}
An alternative would be to use a generic method instead:
class Foo {
public string Value { get; set; }
public Type TheType { get; set; }
public T CastValue<T>() {
return (T)Convert.ChangeType(Value, typeof(T));
}
}
You can also use the System.ComponentModel.TypeConverter classes to convert, since they allow a class to define it's own converter.
Edit: note that when calling the generic method, you must specify the generic type parameter, since the compiler has no way to infer it:
Foo foo = new Foo();
foo.Value = "100";
foo.Type = typeof(int);
int c = foo.CastValue<int>();
You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class:
public object ConvertedValue {
get {
return Convert.ChangeType(Value, Type);
}
}
Properties, events, constructors etc can't be generic - only methods and types can be generic. Most of the time that's not a problem, but I agree that sometimes it's a pain. Brannon's answer gives two reasonable workarounds.
I don't believe the example you've given here is possible. The type of CastedValue has to be defined at compile time, which means it can't depend on a runtime value (the value of the TheType property).
EDIT: Brannon's solution has some good ideas for how to handle this using a generic function rather than a property.