Anchor Sides: what changed

Revision 2 to 3. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		There are some new [[Property\|properties]] and [[Method\|methods]] for automatic layout of controls. You can now setup controls to keep a certain distance to other controls, or center relative to other controls. See below for examples.
2	2
3	3		Each of the four sides of a control (Left, Top, Right, Bottom) can now be anchored/bound to a side of another control. For example you can now anchor the left side of [[TEdit]] to the right side of a [[TLabel]]. Everytime the Label is moved or resized the Edit's left side will follow, which normally results in moving the Edit parallel to the Label.
4	4
5	5		## Example 1
6	6
7		-	~~`+--------+ +-------+`\~~
8		-	~~`\| Label1 \| \| Edit1 \|`\~~
9		-	~~`+--------+ \| \|`\~~
10		-	~~` +-------+`~~
	7	+	```
	8	+	+--------+ +-------+
	9	+	\| Label1 \| \| Edit1 \|
	10	+	+--------+ \| \|
	11	+	+-------+
	12	+	```
11	13
12	14		### In code
13	15
14	16		``` Pascal
15	17		Edit1.AnchorSide[akLeft].Side := asrRight;
16	18		Edit1.AnchorSide[akLeft].Control := Label1;
17	19		Edit1.Anchors := Edit1.Anchors + [akLeft];
18	20		```
19	21
20	22		You can define the distance with the BorderSpacing properties:
21	23
22	24		``` Pascal
23	25		Edit1.BorderSpacing.Left := 10;
24	26		```
25	27
26	28		The same can be done with the method:
27	29
28	30		``` Pascal
29	31		Edit1.AnchorToNeighbour(akLeft, 10, Label1);
30	32		```
31	33
32	34		### Notes
33	35
34	36		The Edit1.Left will follow Label1.Left+Label1.Width, not the other way around. That means, moving Label1 will move Edit1. But moving Edit1 will be undone by the [[LCL]]. If you also anchor the right side of Label1 to the left side of Edit1, you created a circle, and this can result together with some other autosize properties in a loop. This is ignored by the LCL or automagically repaired when the Parent.AutoSize is [[True\|true]].
35	37
36	38		### Via the Anchor Editor
37	39
38	40		The anchor editor is a floating window that is available via the menu View / Anchor Editor or via the button on the Anchors property in the object inspector.
39	41
40	42		![](/wiki-images/2/28/Anchor_Editor_en.png)
41	43
42	44		## Example 2
43	45
44	46		You can anchor the Edit's top side to follow the Label's top side:
45	47
46	48		+--------+ +-------+
47	49		\| Label1 \| \| Edit1 \|
48	50		+--------+ \| \|
49	51		+-------+
50	52
51	53		``` Pascal
52	54		Edit1.AnchorSide[akTop].Side := asrTop;
53	55		Edit1.AnchorSide[akTop].Control := Label1;
54	56		Edit1.Anchors := Edit1.Anchors + [akTop];
55	57		```
56	58
57	59		The same can be done with the method:
58	60
59	61		``` Pascal
60	62		Edit1.AnchorParallel(akTop,0,Label1);
61	63		```
62	64
63	65		## Example 3
64	66
65	67		Centering a Label vertically to an Edit:
66	68
67	69		+-------+
68	70		+--------+ \| \|
69	71		\| Label1 \| \| Edit1 \|
70	72		+--------+ \| \|
71	73		+-------+
72	74
73	75		``` Pascal
74	76		Edit1.AnchorSide[akTop].Side := asrCenter;
75	77		Edit1.AnchorSide[akTop].Control := Label1;
76	78		Edit1.Anchors := Edit1.Anchors + [akTop] - [akBottom];
77	79		```
78	80
79	81		The same can be done with the method:
80	82
81	83		``` Pascal
82	84		Edit1.AnchorVerticalCenterTo(Label1);
83	85		```
84	86
85	87		Obviously anchoring the bottom side of Edit1 does not make sense when centering.
86	88
87	89		## Example 4
88	90
89	91		Using a [[TSplitter]] with the AnchorEditor between two panels: the left panel should behave as if it had `Align=alLeft`, the right panel should behave as if it had `Align=alClient`.
90	92
91	93		- Do not use the `Align` properties of the panels and of the splitter. They must be set to `alNone`. This is important for the splitter for which the default value is `alLeft`.
92	94		- In the anchor editor do the following adjustments:
93	95		- Anchor the top and bottom sides of the panels and the splitter to the corresponding sides of the form.
94	96		- Select the first panel and anchor its left side to the left side of the form and its right side to the left side of the splitter.
95	97		- Select the second panel and anchor its right side to the right side of the form and its left side to the right side of the splitter.
96	98		- The left and right sides of the splitter must not be anchored (as seen from the splitter itself) because this would fix the position of the splitter and make it not movable.
97	99
98	100		The same effect can be achieved by this code:
99	101
100	102		``` pascal
101	103		procedure TForm1.FormCreate(Sender: TObject);
102	104		begin
103	105		with Panel1 do
104	106		begin
105	107		AnchorSideTop.Control := Self;
106	108		AnchorSideBottom.Control := Self;
107	109		AnchorSideBottom.Side := asrBottom;
108	110		AnchorSideLeft.Control := Self;
109	111		AnchorSideRight.Control := Splitter1;
110	112		Anchors := [akLeft, akRight, akTop, akBottom];
111	113		end;
112	114		with Panel2 do
113	115		begin
114	116		AnchorSideTop.Control := Self;
115	117		AnchorSideBottom.Control := Self;
116	118		AnchorSideBottom.Side := asrBottom;
117	119		AnchorSideLeft.Control := Splitter1;
118	120		AnchorSideLeft.Side := asrBottom;
119	121		AnchorSideRight.Control := self;
120	122		AnchorSideRight.Side := asrBottom;
121	123		Anchors := [akLeft, akRight, akTop, akBottom];
122	124		end;
123	125		with Splitter1 do
124	126		begin
125	127		AnchorSideTop.Control := Self;
126	128		Splitter1.AnchorSideBottom.Control := Self;
127	129		AnchorSideBottom.Side := asrBottom;
128	130		Anchors := [akTop, akBottom];
129	131		end;
130	132		end;
131	133		```
132	134
133	135		## New property
134	136
135	137		``` Pascal
136	138		property AnchorSide[Kind: TAnchorKind]: TAnchorSide read GetAnchorSide;
137	139		```
138	140
139	141		This is not published in the [[IDE Window: Object Inspector\|object inspector]]. You can edit it in the designer via the [[IDE Window: Anchor Editor\|anchor editor]] (Menu: View -\> View anchor editor, or click on button of 'Anchors' property).
140	142
141	143		## New methods to easily configure common layouts
142	144
143	145		``` Pascal
144	146		procedure AnchorToNeighbour(Side: TAnchorKind; Space: integer; Sibling: TControl);
145	147		procedure AnchorParallel(Side: TAnchorKind; Space: integer; Sibling: TControl);
146	148		procedure AnchorHorizontalCenterTo(Sibling: TControl);
147	149		procedure AnchorVerticalCenterTo(Sibling: TControl);
148	150		procedure AnchorAsAlign(TheAlign: TAlign; Space: Integer);
149	151		```
150	152
151	153		AnchorVerticalCenterTo works with Parent too. Then it will center on the client area, that means the center of the control is at ClientHeight div 2.
152	154
153	155		Center anchoring is not yet fully supported when computing the size of the parent. For example when you put a label center anchored into a [[TGroupBox\|Groupbox1]] and set Groupbox1.AutoSize to true then Groupbox1 height will shrink leaving no space for the label. The solution is to center to a control that is not centered. For example center a Label1 to a [[TComboBox\|ComboBox]] and use for the ComboBox the default anchors (Anchors=\[akLeft,akTop\]).
154	156
155	157		## Anchoring to invisible controls
156	158
157	159		Anchoring to invisible controls works intuitively. For example: The below controls A, B, C are anchored (C.Left to B.Right and B.Left to A.Right):
158	160
159		-	~~` +---+ +---+ +---+`\~~
160		-	~~` \| A \| \| B \| \| C \|`\~~
161		-	~~` +---+ +---+ +---+`~~
	161	+	```
	162	+	+---+ +---+ +---+
	163	+	\| A \| \| B \| \| C \|
	164	+	+---+ +---+ +---+
	165	+	```
162	166
163	167		If B is hidden (Visible:=[[False\|false]]) then C.Left will skip B and use the right of A, resulting in
164	168
165		-	~~` +---+ +---+`\~~
166		-	~~` \| A \| \| C \|`\~~
167		-	~~` +---+ +---+`~~
	169	+	```
	170	+	+---+ +---+
	171	+	\| A \| \| C \|
	172	+	+---+ +---+
	173	+	```
168	174
169	175		## Circular references
170	176
171	177		You can build circular references by anchoring two sides to each other, which creates an impossible anchoring. The LCL notices that, but will not raise an exception, because it can be a temporary circle. For example: A row of buttons. Button1 is left of Button2, Button2 is left of Button3. Now the order is changed to: Button3, Button1, Button2. If the reanchoring is started with Button3, a circle is created temporarily and is fixed when the reordering is completed. The LCL detects circles and will not move the Button. Circles are not the only anomaly.
172	178
173	179		There is one exception to this rule. If the Parent.AutoSize is true, then the LCL will automatically break circles on autosize and writes a warning via [[DebugLn\|debugln]] (windows: --debug-log.txt, linux, et al: stdout). Which anchor is broken depends on the order of controls and the sides. So, temporary circles are still allowed with AutoSize=true if you enclose the change in
174	180
175	181		``` Pascal
176	182		Parent.DisableAutosizing;
177	183		try
178	184		// change anchors, aligns, bounds...
179	185		finally
180	186		Parent.EnableAutosizing;
181	187		end;
182	188		```
183	189
184	190		The AutoSize algorithm does not only break circles, but fixes Align/AnchorSide inconsistencies too.
185	191
186	192		Eventually it would be good to add some hints in the designer or a tool to list the circles and inconsistencies.
187	193
188	194		## See also
189	195
190	196		- [[Autosize / Layout]]
191	197		- [[Example: Anchors. How to reliably align dynamically created controls under changing visibility]]
192	198
193	199		---
194	200		From the Free Pascal wiki, page "Anchor Sides", as it stood on 2021-10-11 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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