conditional-commands.md

Conditional commands

Commands which cannot currently be used, but should still be available in the menu tree at other times, can disable themselves. Disabled commands cannot be used and are not listed by help.

In this example, a global flag (bool myEnabledProperty) is used to determine if a command is enabled. It is initially cleared, the enable command sets it.

m.Add ("enable", s => myEnabledProperty = true);

Create a new inline command, then set its enabledness function so it returns the above flag.

var mi = m.Add ("inline", s => Console.WriteLine ("Disabled inline command was enabled!"));
mi.SetEnablednessCondition (() => myEnabledProperty);

$ inline
Unknown command: inline
$ enable
$ inline
Disabled inline command was enabled!

It is also possible to override the enabledness by subclassing.

private class DisabledItem : CMenuItem
{
	public DisabledItem ()
		: base ("subclassed")
	{
		HelpText = "This command, which is defined in its own class, is disabled by default.";
	}

	public override bool IsEnabled ()
	{
		return myEnabledProperty;
	}

	public override void Execute (string arg)
	{
		Console.WriteLine ("Disabled subclassed command was enabled!");
	}
}

$ subclassed
Unknown command: subclassed
$ enable
$ subclassed
Disabled subclassed command was enabled!

Disabled commands are not displayed by help.

$ help
Available commands:
e   | enable
h   | help
q   | quit
$ enable
$ help
Available commands:
e   | enable
h   | help
i   | inline
q   | quit
s   | subclassed

Command abbreviations do not change when disabled items become enabled, i.e. it is made sure they are already long enough to be unique. This avoids confusion about abbreviations suddenly changing.

m.Add ("incollision", s => Console.WriteLine ("The abbreviation of 'incollision' is longer to account for the hidden 'inline' command."));

$ help
Available commands:
e   | enable
h   | help
inc | incollision
q   | quit
$ enable
$ help
Available commands:
e   | enable
h   | help
inc | incollision
inl | inline
q   | quit
s   | subclassed