react input 獲取/失去焦點

<div className={ this.state.focus ? "dis_bottom_left_onfocus" : "dis_bottom_left" } ref="bottom_left">
    <input
        type="text"
        className="dis_bottom_input"
        ref="bottom_input"
        placeholder={this.props.mainName || "說點什么吧"}
        onBlur={ ::this.inputOnBlur }
        onFocus={ ::this.inputOnFocus } />
</div>

//input 獲取焦點 width: 100%
inputOnFocus(){
    this.setState({ focus: true });
}

//input 失去焦點
inputOnBlur(){
    this.setState({ focus: false });
}