how to set xfce's panel plugin width - gtk

Question

I build one simple xfce panel plugin which dispalys a button labeled as 'Hello World". However, only half of the string can be displayed.
http://en.zimagez.com/miniature/debian807092016010347.png
The code is simple:
#include <gtk/gtk.h>
#include <libxfce4panel/xfce-panel-plugin.h>
static void sample_construct(XfcePanelPlugin *plugin);
XFCE_PANEL_PLUGIN_REGISTER(sample_construct);
static void hello(GtkWidget *widget, gpointer data)
{
g_print("Hello World\n");
}
static void sample_construct(XfcePanelPlugin *plugin)
{
GtkWidget *button;
button = gtk_button_new_with_label ("Hello World");
g_signal_connect (button, "clicked", G_CALLBACK (hello), NULL);
gtk_container_add (GTK_CONTAINER (plugin), button);
gtk_widget_show (button);
}
build and install with this script:
#!/bin/bash
gcc -Wall -shared -o libsample.so -fPIC sample.c $(pkg-config --cflags --libs libxfce4panel-1.0) $(pkg-config --cflags --libs gtk+-2.0) || \
{ echo "Compiling failed!"; exit 10; }
cp libsample.so /usr/lib/xfce4/panel-plugins
cp sample.desktop /usr/share/xfce4/panel-plugins
OTHER INFO: xfce4.10, Debian 8 jessie.

Answer 1

You missed the "size-changed" signal.
If you add the following code it's going to work as expected:
static gboolean
sample_size_changed (XfcePanelPlugin *plugin,
gint size,
void *data)
{
GtkOrientation orientation;
orientation = xfce_panel_plugin_get_orientation (plugin);
if (orientation == GTK_ORIENTATION_HORIZONTAL)
gtk_widget_set_size_request (GTK_WIDGET (plugin), -1, size);
else
gtk_widget_set_size_request (GTK_WIDGET (plugin), size, -1);
return TRUE;
}
static void sample_construct(XfcePanelPlugin *plugin)
{
...
g_signal_connect (G_OBJECT (plugin), "size-changed",
G_CALLBACK (sample_size_changed), NULL);
gtk_widget_show_all (button);
}
Pay attention that you're also missing important callbacks such as "free-data" and "orientation-changed". Note that since Xfce 4.12, GTK+ 3.0 plugins are also supported, you only need to set X-XFCE-API=2.0 in .desktop file.
Source: xfce4-sample-plugin