Visualforce 'Conversion Error setting value' -- binding problem with selectCheckboxes

I am getting a 'Conversion error setting value' when I try to save a record in my controller extension. The page looks the way I would expect, but when I select one or more checkboxes, it gives my that error. I'm not seeing what the error is here. Thanks for the help.

The page:

          <apex:pageBlockSectionItem >
                <apex:OutputLabel value="Assigned Areas of Coverage" for="books" />
                <apex:selectCheckboxes value="{!selectedBooks}"
                    layout="pageDirection" id="books">
                    <apex:selectOptions value="{!options}" />
                </apex:selectCheckboxes>
            </apex:pageBlockSectionItem>

The controller:

public String[] selectedBooks {get; set;}

public List<SelectOption> options 
{
    get
    {
        List<SelectOption> result = new List<SelectOption>();
        List<String> optionNames = bookNames(books);
        optionNames.sort();

        for(String n : optionNames){
            if(!blacklist.contains(n)){
                result.add(new SelectOption(n, n));
            }
        }

        return result;
    }
}

private List<Book__c> books 
{
    get 
    { if (books == null){
        books =   [select Id, Name from Book__c];
        }
        return books;

    }
    set;    
}

private List<String> bookNames(List<Coverage__c> coverage)
{
    List<String> result = new List<String>();

    for(Coverage__c c : coverage){
        result.add(c.Book__r.Name);
    }

    return result;
}

private List<String> bookNames(List<Book__c> books)
{
    List<String> result = new List<String>();

    for(Book__c b : books){
        result.add(b.Name);
    }

    return result;
}

private List<Id>开发者_运维知识库; bookIDs(List<String> bookNames)
{
    List<Id> result = new List<Id>();
    Set<String> bookNamesSet = new Set<String>(bookNames);

    for(Book__c b : books){
        if(bookNamesSet.contains(b.Name)){
            result.add(b.Id);
        }
    }

    return result;
} 

I think you have to post more code and it's not clear what exactly you wish to achieve:

• What's your actual "command" function, I don't see any <apex:commandButton action="{!fun}" ... > and not a single function from the controller looks like "public void fun()" or "public PageReference fun()" - I especially mean the part about taking no input arguments.

• Your code does not compile, I've replaced Book__c with Account and Coverage with Contact, but for example the "blacklist" variable in

  if(!blacklist.contains(n)){

is undefined. I can assume that this is same as "result", but you know... garbage in, garbage out. We might need just the part you've omitted ;) Also - can you replicate the problem using standard Salesforce objects so it's easier to test for us?

• "selectedBooks" is read in the page but you never set value? Not even to the simplest selectedBooks = new String[]... The uninitialized variable a is solution to similar problem discussed on Salesforce message board.

• Just a random thought - for bookIDs() function you might be better using Map<Id, Book__c> or Map<Id, String>. The first one can even be instantiated directly from [SELECT Id, Name FROM Book] if you need it. You want set of IDs - use the keySet() method afterwards. You want a list of books - use the values().