Conversion Error setting value 'value1 value2 value3' for '#{myMultiselectPicklistValue}'.

Salesforce is great. Apex is great. Visualforce is great.

Until you run into bizarre errors with no obvious explanation, such as the following error:

Conversion Error setting value 'value1 value2 value3' for '#{myMultiselectPicklistValue}'.

This error comes from trying to save the selections from an apex:selectCheckboxes component into a multi-select picklist field. You would think that it's as easy as simply specifying {!property} for the value attribute of the apex:selectCheckboxes component. But, no, it's not.

Multi-select picklist values are stored as String values, with each option delimited with a semicolon.  This is great to know, but what happens with apex:selectCheckboxes? apex:selectCheckboxes expects a List<String>! This discussion board post hints at the annoyance awaiting developers: "Checkboxes not saving".

Basically, to spell it out for myself and for others, here's what we have to do as developers working around this problem.

What we want to write is:


<apex:selectcheckboxes value="{!mPicklistValue}">

... and in the controller ...


public String mPicklistValue { get; set; }

Instead, what we have to write is:


<apex:selectcheckboxes value="{!mPicklistValues}">

... and in the overblown controller ...

private String mPicklistValue;
public List<String> getMPicklistValues() {
    List<String> values = null;
    // Convert mPicklistValue into List of 
    // String values

    if (mPicklistValue != null)
        values = mPicklistValue.split(';');

    return values;
}   // List<String> getMPicklistValues()
public void setMPicklistValues(
        List<String> values) {

    // Convert values into a semilcolon-delimited
    // String value

    if (values == null) {
        mPicklistValue = null;
    }
    else {
        mPicklistValue = '';
        
        for (String value : values) {
            mPicklistValue += value + ';';
        }
    }
}   // void setMPicklistValues(List<String>)

Note the plural name of the custom getter and setter methods. Cheers, indeed.