getData:function(callback){
     if(!callback){
       callback = res=>{}
     }
     wx.showLoading({
       title: '数据加载中',
      
     })
     console.log('1')
    todos.skip(this.pageData.skip).get().then(res =>{
      this.setData({
        tasks:res.data
      })
    },res =>{
      console.log('2')
      this.pageData.skip = this.pageData.skip + 20
      wx.hideLoading()
      console.log('2')
      callback();
      
    })
   },