a9fb8ac1c3
First on constant variable issue:
This will not compile:
[Plugin(MyPluginName)] // Won't compile because MyPluginName isn't const
[Plugin(MyConstPluginName)] // OK
[Plugin("My Cool Plugin")] // OK
In order to access properties on the static class, it must specify the name of the class before the properties name as proposed on this change:
[Plugin(Variables.MyPluginName)] // Won't compile because MyPluginName isn't const
[Plugin(Variables.MyConstPluginName)] // OK
[Plugin("My Cool Plugin")] // OK
Second on access on attribute properties:
In order to access plugin.Name on this code:
var type = typeof(MyPlugin); // Returns a Type object representing our MyPlugin class
var attributes = System.Attribute.GetCustomAttributes(type); // Returns an Attribute[]
foreach (var a in attributes)
{
if (a is PluginAttribute plugin)
Console.WriteLine($"Plugin Name: {plugin.Name}");
}
You need to cast if first to the right class, then access the properties, as the above code will generate a compile-time error:
var type = typeof(PluginAttribute); // Returns a Type object representing our PluginAttribute class
var attributes = System.Attribute.GetCustomAttributes(type); // Returns an Attribute[]
foreach (var a in attributes)
{
if (a is PluginAttribute)
{
PluginAttribute plug = (PluginAttribute)a; //Cast it first to PluginAttribute class before you can access all accessible properties
Console.WriteLine($"Plugin Name: {plug.Name}");
}
}
2.7 KiB
title
| title |
|---|
| Attributes |
Attributes
Attributes allow the programmer to add metadata to assemblies, types, and members. When applied to a type or member, an attribute will take the form of [Attribute] or [Attribute(args)]. When applied to an assembly, an attribute will take the form of [assembly:Attribute] or [assembly:Attribute(args)].
An attribute is any class that inherits from the parent Attribute type. Conventionally, the name of an attribute in its definition will be SomethingAttribute, rather than just Something. When used, [Something] will still compile:
public class PluginAttribute : Attribute
{
// Attribute members
}
[Plugin]
public class MyPlugin
{
// Plugin members
}
As mentioned above, attributes can have constructors like any other class. However, all arguments in an attribute constructor must be compile-time constants.
public static class Variables // For the purposes of demonstration
{
public static string MyPluginName = "Cool Plugin";
public const string MyConstPluginName = "Amazing Plugin";
}
public class PluginAttribute : Attribute
{
public string Name { get; private set; }
public PluginAttribute(string name)
{
Name = name;
}
}
[Plugin(Variables.MyPluginName)] // Won't compile because MyPluginName isn't const
[Plugin(Variables.MyConstPluginName)] // OK
[Plugin("My Cool Plugin")] // OK
public class MyPlugin
{
// Plugin members
}
Accessing a Type's Attributes
The System.Attribute.GetCustomAttributes(Type) method returns an array of all the attributes applied to a type. The programmer can then loop through this array to find the desired attribute using the is keyword.
public void PrintPluginName()
{
var type = typeof(PluginAttribute); // Returns a Type object representing our PluginAttribute class
var attributes = System.Attribute.GetCustomAttributes(type); // Returns an Attribute[]
foreach (var a in attributes)
{
if (a is PluginAttribute)
{
PluginAttribute plug = (PluginAttribute) a; //Cast it first to PluginAttribute class before you can access all accessible properties
Console.WriteLine($"Plugin Name: {plug.Name}");
}
}
}