[maemo-developers] Something strange when setting the color of the widget

[From: Kalle Vahlman]

2008/3/19, LIU Chun Hung <hungsiu at ust.hk>:
> Hi,
>
>  I want to create three buttons with different colors. But three buttons
>  are with the same colors at the final. What's wrong? Anybody help? My
>  program code is as below:
[snip]
>  bn1_style = gtk_widget_get_style(bn1);
>  bn1_style->bg[GTK_STATE_NORMAL] = red_color;
>  gtk_widget_set_style(bn1, bn1_style);
>  bn2_style = gtk_widget_get_style(bn2);
>  bn2_style->bg[GTK_STATE_NORMAL] = green_color;
>  gtk_widget_set_style(bn2, bn2_style);
>  bn3_style = gtk_widget_get_style(bn3);
>  bn3_style->bg[GTK_STATE_NORMAL] = blue_color;
>  gtk_widget_set_style(bn3, bn3_style);
>
>  Three buttons are in blue at the final.

That's because gtk_widget_get_style() returns the active style object
for a widget, which very likely is exactly the same object for all
button widgets.

So first of all, NEVER TOUCH THE STYLE OBJECTS MEMBERS DIRECTLY. This
is not going to be even possible for much longer, and it is generally
very bad (though very often used) practise to change an objects
members directly. In this case it ends up modifying the property for
all widgets that share the style object.

To make it work as intended you can use the gtk_widget_modify_*()
functions to change the appearance of a widget. But note that this too
is considered bad practise unless you have a very specific needs
and/or control all aspects of the appearance (in order to not have
black text on black background for example) regardless of any
user-selected GTK+ theme.

-- 
Kalle Vahlman, zuh at iki.fi
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