React CSSTransitionGroup动画不起作用

Question

我正在尝试以下简单的显示/隐藏动画，该项目确实出现并消失，但没有任何动画：

toggleChangePassword = () => {
  this.setState({ showChangePassword: !this.state.showChangePassword })
}

....

<button onClick={this.toggleChangePassword}>Forgot your password?</button>

<CSSTransitionGroup
  transitionName="example"
  transitionEnterTimeout={500}
  transitionLeaveTimeout={300}>
  {this.state.showChangePassword && changePassword}
</CSSTransitionGroup>