Swing Custom Layout Managers

[jsulman]

I am currently wrestling with Swing custom LayoutManagers. The book I am using gives a pretty simple example but I cannot follow the sequence of methods that are fired off when a panel has a layout manager set to it and when a component is added to it. Does anybody know how the methods are fired?
The LayoutManager has 5 methods:

addLayoutComponent(String name, Component comp)
layoutContainer(Container parent),
minimumLayoutSize(Container parent),
preferredLayoutSize(Container parent)
removeLayoutComponent(Component parent)

Which of these are executed when the Layout is set to a panel (p1.setLayout(LayoutManager mgr) and when a component is added to the panel. This would sure make it easier to understand the example I am working through. Or could you direct me to some documentation that would explain this.

Thanks in advance

Jeff Sulman

 

[Swamphen]

for instance:

panel.setLayout(new BorderLayout());
-> setLayout-method of class Container is executed:

//////////////////////code/////////////////////
layoutMgr = mgr;
if (valid) {
invalidate();
}
///////////////////////////////////////////////

The invalidate-method marks the container and all
of the parent components as possibly "not lay-
outed".

panel.add(new TextArea(),"center"

-> add(Component comp, Object constraints) from
Container-class is executed


//////////////////////code//////////////////////
addImpl(comp, constraints, -1);
////////////////////////////////////////////////


-1 because we didn't provide an index in the add-
message; if you do that you can place the new com
ponent at a certain position in the row of
components of that container.


-> addImpl-method of class Container

/////////////////////////////////////////////////////
protected void addImpl(Component comp, Object
constraints, int index) {
.....

if (valid) {invalidate();}

.....

if (layoutMgr != null) {
layoutMgr.addLayoutComponent((String)constraints,
comp);
}
}
////////////////////////////////////////////////////////

-> addLayoutComponent-methods of class BorderLayout (in
this case)

////////////////////////////////////////////////////////
public void addLayoutComponent(Component comp, Object
constraints) {
...
addLayoutComponent((String)constraints, comp);
...
}
///////////////////////////////////////////////////
public void addLayoutComponent(String name, Component
comp) {
...
if (name == null) {
name = "Center";
}

if ("Center".equals(name)) {
center = comp;
}
...
////////////////////////////////////////////////////////


So, you should notice the container is left in an invalidated state after assiging a layout manager or
adding a component. So you should always perform the
container.validate()-method afterwards.

Greetings,
Swamphen

 

[jsulman]

Swamphen,
Thanks for your detailed response. I have two more quick questions. First, where did you get this infor from? The Java Source Code? If so where can I get the JSC?

Second, in most of the custom gridlayouts I notice that the preferredLayoutSize(Component comp) does a lot of the work. How does this fit into the picture? When is it called?

Thanks Again.

 

[Swamphen]

Java Source
-----------


This link should provide you with the Java Source code:

http://www.sun.com/software/communitysource/java2/index.html

preferredLayoutSize(Component comp)
-----------------------------------


When you call the validate() method to set the layout of the components of a container right, the following method-sequence arises:

1) container.validate();
2) container.layout();
3) layoutmanager.layoutContainer(container);
4) somewhere along the layouting in that method,
for each of the components in that container:
component.getPreferredSize();
5) if the component is a container itself, this last method
will lead to the invokement of:
thats_components_layoutmanager.preferredLayoutsize(that
_component);

In this last method the preferred sizes of the components in the component/container are used to determine an overal
preferred size of the container for the chosen layout.

I hope things are starting to clear now?

Swamphen