Update Ext.form.Text inputCls

[sissonb]

I have a text form and want to update the inputCls property on keyup. This is how I am currently trying, but it's wrong.

new Ext.form.Text({            
            name : 'referredFrom',
            id : 'referredFrom',
            inputCls:"invalid",
            label: 'Account Number',
            listeners:{
                keyup:function(){
                    
                    var isValid = true;
                    if(isValid){
                        Ext.getCmp("referredFrom").inputCls = "valid";                        
                    }
                    else{                        
                        Ext.getCmp("referredFrom").inputCls = "invalid";
                    }
                }
            }
        });

Any Ideas?
Thanks

[sissonb]

Currently I am doing it this way, but really don't like the solution.

new Ext.form.Text({
            name : 'referredFrom',
            id : 'referredFrom',
            label: 'Account Number',
            listeners:{
                keyup:function() {


                    if (this.getValue() === "") {
                        var defaultClass = "x-input-text";
                        Ext.getCmp("referredFrom").el.dom.children[1].children[0].setAttribute("class", defaultClass);
                    }
                    else {
                        var unknownClass = "x-input-text unknown";
                        Ext.getCmp("referredFrom").el.dom.children[1].children[0].setAttribute("class", unknownClass);
                    }
                }
            }
        });

If there is a better way please let me know.
Thanks