[Seaside] anchors behaving like buttons?

[Nevin Pratt]

Derek Brans wrote:

> In Seaside, is there a way to have an anchor tag that will submit a 
> form and perform an action (behaving just like a button)?
>

I've got a scheme that seems to work OK:

Suppose you've got a component 'Foo', with launch URL of 
'http://localhost/seaside/foo' (or whatever machine and port you 
choose).  Now, suppose the 'Foo' component has links 'red' and 'green' 
in the GUI, which you want to use to invoke methods #red and #green on 
component Foo when the links are clicked on.

1. Define the URL for the 'red' link to be '/seaside/foo/red', and for 
the 'green' link to be '/seaside/foo/green'.

2. Give 'Foo' an instance variable called 'targets', and then create an 
#initialize method of 'Foo' thus:

   initialize
       targets _ OrderedCollection new.
       targets add: #red;
            add: #green

3. Give 'Foo' a 'lastTarget' instance variable, which will be used to 
prevent recursive circularities, as shown later.

4. Put the following in Foo's #renderContentOn:

   renderContentOn: html
       | path sel |
       path _ self session path.
       sel _ (path copyAfterLast: $/) asLegalSelector asSymbol.
       (lastTarget ~= sel
            and: [targets includes: sel])
        ifTrue: [lastTarget _ sel.
            ^self perform: sel].
      { ... the rest of the normal rendering code here ... }

With the above, the 'red' and 'green' links will invoke the #red and 
#green target methods (respectively) of the component, just like a 
button does.

You can, if you wish, easily eliminate the need for the 'targets' 
instance variable by, for example, looking for methods within a certain 
method category, or for methods that begin (or end) with some common 
string, or even be more general by replacing 'targets includes: sel' 
with something like 'self respondsTo: sel', but I think I would prefer 
to keep strict control over what methods can be invoked via the URL with 
this scheme.  So, I would use a 'targets' instance variable to 
explicitly define allowable methods that can be invoked with this scheme.

Nevin