registerInput in Combobox

[kennyhk]

i need to assign property "ref" as my like, because i need to control the focus/blur behavior manually.

The problem is, i don't know how the "registerInput" work in Combobox, registerInput alway return undefined in following codes :

        let props = {
            options: options,
            onChange: this.onChange,
            onSelect: this.onSelect,
            autocomplete: true,
            autosize: true
            registerInput: ()=> {
                return <input type="search" ref="keyword" value={this.state.value} />;
            }
        };

        return <Combobox {...props} >
        {
            (inputProps, otherProps, registerInput) => {
                inputProps.type = "search";
                inputProps.ref = (c) => {
                    let ref = registerInput(ReactDOM.findDOMNode(c));
                    console.log(ref);   // <- alway undefined
                    return ref;
                };
                return <input {...inputProps}/>;
            }
        }
        </Combobox>;

can you let me know what is my mistake please?