2 <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
3 "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
5 <chapter id="gtk-migrating-GtkGrid">
7 <title>Migrating from other containers to GtkGrid</title>
10 #GtkGrid is an attempt to write a comprehensive, legacy-free,
11 box-layout container that is flexible enough to replace #GtkBox,
12 #GtkTable and the like.
16 The layout model of GtkGrid is to arrange its children in rows and
17 columns. This is done by assigning positions on a two-dimentions
18 grid that stretches arbitrarily far in all directions.
19 Children can span multiple rows or columns, too.
24 <title>GtkBox versus GtkGrid: packing</title>
27 GtkBox works by arranging child widgets in a single line, either
28 horizontally or vertically. It allows packing children from the
29 beginning or end, using gtk_box_pack_start() and gtk_box_pack_end().
32 <inlinegraphic fileref="box-packing.png" format="PNG"></inlinegraphic>
35 <title>A simple box</title>
37 box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
39 gtk_box_pack_start (GTK_BOX (box), gtk_label_new ("One"), FALSE, FALSE, 0);
40 gtk_box_pack_start (GTK_BOX (box), gtk_label_new ("Two"), FALSE, FALSE, 0);
42 <para>This can be done with #GtkGrid as follows:</para>
44 grid = gtk_grid_new ();
46 child1 = gtk_label_new ("One");
47 gtk_grid_attach (GTK_GRID (grid), child1, 0, 0, 1, 1);
48 child2 = gtk_label_new ("Two");
49 gtk_grid_attach_next_to (GTK_GRID (grid), child2, child1, GTK_POS_RIGHT, 1, 1);
52 And similarly for gtk_box_pack_end(). In that case, you
53 would use #GTK_POS_LEFT to place the grid children from
57 If you only need to pack children from the start, using
58 gtk_container_add() is an even simpler alternative. GtkGrid
59 places children added with gtk_container_add() in a single
60 row or column according to its #GtkOrientable:orientation.
65 One difference to keep in mind is that the gtk_box_pack_start/pack_end
66 functions allow you to place an arbitrary number of children from
67 either end without ever 'colliding in the middle'. With GtkGrid, you
68 have to leave enough space between the two ends, if you want to combine
69 packing from both ends towards the middle. In practice, this should be
70 easy to avoid; and GtkGrid simply ignores entirely empty rows or
71 columns for layout and spacing.
74 On the other hand, GtkGrid is more flexible in that its grid extends
75 indefinitively in both directions — there is no problem with
76 using negative numbers for the grid positions. So, if you discover
77 that you need to place a widget before your existing arrangement,
83 <title>GtkBox versus GtkGrid: sizing</title>
86 When adding a child to a GtkBox, there are two hard-to-remember
87 parameters (child properties, more exactly) named expand and fill
88 that determine how the child size behaves in the main direction
89 of the box. If expand is set, the box allows the position occupied
90 by the child to grow when extra space is available. If fill is
91 also set, the extra space is allocated to the child widget itself.
92 Otherwise it is left 'free'.
93 There is no control about the 'minor' direction; children
94 are always given the full size in the minor direction.
97 <inlinegraphic fileref="box-expand.png" format="PNG"></inlinegraphic>
100 GtkGrid does not have any custom child properties for controlling
101 size allocation to children. Instead, it fully supports the newly
102 introduced #GtkWidget:hexpand, #GtkWidget:vexpand, #GtkWidget:halign
103 and #GtkWidget:valign properties.
106 The #GtkWidget:hexpand and #GtkWidget:vexpand properties operate
107 in a similar way to the expand child properties of #GtkBox. As soon
108 as a column contains a hexpanding child, GtkGrid allows the column
109 to grow when extra space is available (similar for rows and vexpand).
110 In contrast to GtkBox, all the extra space is always allocated
111 to the child widget, there are no 'free' areas.
114 To replace the functionality of the fill child properties, you can
115 set the #GtkWidget:halign and #GtkWidget:valign properties. An
116 align value of #GTK_ALIGN_FILL has the same effect as setting fill
117 to %TRUE, a value of #GTK_ALIGN_CENTER has the same effect as setting
118 fill to %FALSE. The image below shows the effect of various combinations
119 of halign and valign.
122 <inlinegraphic fileref="widget-hvalign.png" format="PNG"></inlinegraphic>
125 <title>Expansion and alignment</title>
127 box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
129 gtk_box_pack_start (GTK_BOX (box), gtk_label_new ("One"), TRUE, FALSE, 0);
130 gtk_box_pack_start (GTK_BOX (box), gtk_label_new ("Two"), TRUE, TRUE, 0);
132 <para>This can be done with #GtkGrid as follows:</para>
134 grid = gtk_grid_new ();
136 child1 = gtk_label_new ("One");
137 gtk_widget_set_hexpand (child1, TRUE);
138 gtk_widget_set_halign (child1, GTK_ALIGN_CENTER);
139 gtk_grid_attach (GTK_GRID (grid), child1, 0, 0, 1, 1);
140 child2 = gtk_label_new ("Two");
141 gtk_widget_set_hexpand (child2, TRUE);
142 gtk_widget_set_halign (child1, GTK_ALIGN_FILL);
143 gtk_grid_attach_next_to (GTK_GRID (grid), child2, child1, GTK_POS_RIGHT, 1, 1);
147 One difference between the new GtkWidget expand properties and
148 the GtkBox child property of the same name is that widget expandability
149 is 'inherited' from children. What this means is that a container
150 will become itself expanding as soon as it has
151 an expanding child. This is typically what you want, it lets
152 you e.g. mark the content pane of your application window as
153 expanding, and all the intermediate containers between the
154 content pane and the toplevel window will automatically do
155 the right thing. This automatism can be overridden at any
156 point by setting the expand flags on a container explicitly.
159 Another difference between GtkBox and GtkGrid with respect to
160 expandability is when there are no expanding children at all.
161 In this case, GtkBox will forcibly expand all children whereas
162 GtkGrid will not. In practice, the effect of this is typically
163 that a grid will 'stick to the corner' when the toplevel
164 containing it is grown, instead of spreading out its children
165 over the entire area. The problem can be fixed by setting some
166 or all of the children to expand.
170 When you set the #GtkBox:homogeneous property on a GtkBox,
171 it reserves the same space for all its children. GtkGrid does
172 this in a very similar way, with #GtkGrid:row-homogeneous and
173 #GtkGrid:column-homogeneous properties which control whether
174 all rows have the same height and whether all columns have
180 <title>GtkBox versus GtkGrid: spacing</title>
183 With GtkBox, you have to specify the #GtkBox:spacing when
184 you construct it. This property specifies the space that
185 separates the children from each other. Additionally, you
186 can specify extra space to put around each child individually,
187 using the #GtkBox:padding child property.
191 GtkGrid is very similar when it comes to spacing between the
192 children, except that it has two separate properties,
193 #GtkGrid:row-spacing and #GtkGrid:column-spacing, for the
194 space to leave between rows and columns. Note that row-spacing
195 is the space <emphasis>between</emphasis> rows, not inside
196 a row. So, if you doing a horizontal layout, you need to set
197 #GtkGrid:column-spacing.
200 GtkGrid doesn't have any custom child properties to specify
201 per-child padding; instead you can use the #GtkWidget:margin
202 property. You can also set different padding on each side with
203 the #GtkWidget:margin-left, #GtkWidget:margin-right,
204 #GtkWidget:margin-top and #GtkWidget:margin-bottom properties.
208 <title>Spacing in boxes</title>
211 box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 6);
212 gtk_box_pack_start (GTK_BOX (box), child, FALSE, FALSE, 12);
214 <para>This can be done with #GtkGrid as follows:</para>
216 grid = gtk_grid_new ();
217 gtk_grid_set_row_spacing (GTK_GRID (grid), 6);
218 g_object_set (child, "margin", 12, NULL);
219 gtk_grid_attach (GTK_GRID (box), child, 0, 0, 1, 1);
226 <title>GtkTable versus GtkGrid</title>
227 cover here: spanning, attachment points, grid size, attach options vs expand/align