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Corrected access on constant variable and access on attribute properties. (#36586)

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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}");
                    }
	}
This commit is contained in:
Willy David Jr
2019-08-21 00:32:05 +08:00
committed by Randell Dawson
parent ad5b99ed09
commit a9fb8ac1c3
1 changed files with 8 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
guide/english/csharp/attributes/index.md
View File

@ -37,8 +37,8 @@ public class PluginAttribute : Attribute
} }
} }
[Plugin(MyPluginName)] // Won't compile because MyPluginName isn't const [Plugin(Variables.MyPluginName)] // Won't compile because MyPluginName isn't const
[Plugin(MyConstPluginName)] // OK [Plugin(Variables.MyConstPluginName)] // OK
[Plugin("My Cool Plugin")] // OK [Plugin("My Cool Plugin")] // OK
public class MyPlugin public class MyPlugin
{ {
@ -51,13 +51,16 @@ The `System.Attribute.GetCustomAttributes(Type)` method returns an array of all
```csharp ```csharp
public void PrintPluginName() public void PrintPluginName()
{ {
var type = typeof(MyPlugin); // Returns a Type object representing our MyPlugin class var type = typeof(PluginAttribute); // Returns a Type object representing our PluginAttribute class
var attributes = System.Attribute.GetCustomAttributes(type); // Returns an Attribute[] var attributes = System.Attribute.GetCustomAttributes(type); // Returns an Attribute[]
foreach (var a in attributes) foreach (var a in attributes)
{ {
if (a is PluginAttribute plugin) if (a is PluginAttribute)
Console.WriteLine($"Plugin Name: {plugin.Name}"); {
PluginAttribute plug = (PluginAttribute) a; //Cast it first to PluginAttribute class before you can access all accessible properties
Console.WriteLine($"Plugin Name: {plug.Name}");
}
} }
} }
``` ```