在微信小程序中如何使用toast消息对话框

<form bindsubmit="formBindsubmit" bindreset="formReset">
 <view style="display:flex;">
  <label>用户名：</label>
  <input name="userName" placeholder="请输入用户名！" />
 </view>
 <view style="display:flex;">
  <label>密码：</label>
  <input name="psw" placeholder="请输入密码！" password="true" />
 </view>
 <view style="display:flex;margin-top:30px;">
  <button style="width:30%;" formType="submit" >登录</button>
  <button style="width:30%" formType="reset" >重置</button>
 </view>
</form>
<view>{{userName}}</view>
<view>{{psw}}</view>
<toast duration="2000" hidden="{{toastHidden}}" bindchange="toastBindChange">用户名或密码不能为空！</toast>

Page({
 data:{
  // text:"这是一个页面"
  toastHidden:true,
  userName:'',
  psw:''
 },
 formBindsubmit:function(e){
  if(e.detail.value.userName.length==0||e.detail.value.psw.length==0){
   this.setData({
    toastHidden:!this.data.toastHidden
   })
  }else{
   this.setData({
    tip:'',
    userName:'用户名：'+e.detail.value.userName,
    psw:'密码：'+e.detail.value.psw
   })
  }
 },
 formReset:function(){
  this.setData({
   userName:'',
   psw:''
  })
 },
 toastBindChange:function(){
  this.setData({
    toastHidden:!this.data.toastHidden
  })
 }
})