Re: [Vala] Passing user_data in signals is supported, but could be better.

[Alexandre Rosenfeld <alexandre rosenfeld gmail com>]

Why not just use lambda? From the Gtk+
example<http://live.gnome.org/Vala/GTKSample>
:

    var button = new Button.with_label ("Click me!");
    button.clicked.connect (() => {
        button.label = "Thank you";

        this.my_data = 3;
    });

And you can have that my_data be anything you want, an instance member or a
property in any other instance (doesnt have to be from *this*).

*Alexandre Rosenfeld*

2011/10/10 Tal Hadad <tal_hd hotmail com>

> Vala does support passing a "context" argument, calling user_data to
> callbacks,
> by this two methods(source: FAQ and Tutorial):
> 1. Passing "this"/self as user_data, for instance method.
> 2. Variables outside the lambda expression.
> Method 2 is done perfectly by Vala, when we talk about lambda expression.
> But method 1 is not enough... Not always it's "this"/self what that needed
> to be
> passed.
> By now, two ways to overcome this, without using lambda:
> * The dirty trick:
> instance.event_name.connect (((instance_type*)user_data)->method);
> ...
> private void method ([args]) {
>    user_data_type* user_data = this;
>    // Perform action with user_data.
> }
>
> * Back to basic(using GLib.Signal namespace):
> Signal.connect (instance, "event_name", (GLib.Callback)method, user_data);
> ...
>
> private static void static_on_stop_clicked ([args], user_data_type
> user_data) {
>
>    // Perform action with user_data.
>
> }
>
> Both works, but I think a proper syntax should be.
> I really like the instance.method way for passing callbacks, but it's valid
> only for
> "this"/self. So, perhaps, instance:method for static methods?
> What do you think? Shell Vala support this feature?
> Tal
>
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