Почему refs возврощает undefined??? func = () => {

Question

Почему refs возврощает undefined??? func = () => {

var funct = this.refs.taskName.value;
alert (funct);
}
<TextField
id="outlined-multiline-static"
ref="taskName"
style={CSSStylesecond}
label="Описание задачи"
multiline
rows="4"
className={classes.textField}
margin="normal"
variant="outlined"
/>
<BottomNavigationAction className={classes.colorsave} onClick={this.func} label="Сохранить" value="save" icon={<CheckCircleOutline />} />