Populating multiselect picklist from page reference

Question

I'm sending some parameters to custom controller of my object, which should be populated on multiselect picklist. In controller I'm creating a new Page Reference, where I put all parameters by using myPage.getParameters.put('fieldId', 'paramValue'). This is for creating new instance of object with some fields preselected upon creating on creation page.

I need to set multiple values into multiselect field, and I'm trying to do it by joining all needed values with ;, but SF doesn't understand this.

Then, I'm put into Page Reference constructor URL with all values for this field 'myId=val1&myId=val2'. This also doesn't work.

Finally, I'm trying to put all into one parameter and send it as one value, like: myPage.getParameters.put('fieldId', 'val1&fieldId=val2'), but here I'm facing the problem of encoding all letters, including = and & which definitely should be kept as usual. Can anyone suggest how to do it through page reference?

Answer 1

You can't do this with a PageReference. The correct syntax is indeed myId=val1&myId=val2, but you can't codify this in a PageReference because the query string gets parsed in to a Map<String, String>. In order to redirect successfully, you'd have to use client-side JavaScript and use a normal string:

<script>
var redirurl = "{!redirect}";
if(redirurl) {
  window.location = redirurl;
}
</script>

There's absolutely no way to hack this with server-side code, as far as I can tell.