微信小程序wx.getImageInfo()如何获取图片信息

<view class="zn-uploadimg">  
  <image src="{{tempFilePaths}}" mode="aspecFill" style="width: 100%; height: 450rpx" />  
  <text>图片的大小：{{imgwidth}}px*{{imgheight}}px</text> 
</view> 

var app = getApp()  
Page({ 
  data: {  
    tempFilePaths: '../uploads/foods.jpg', 
    imgwidth:0, 
    imgheight:0,  
  }, 
  onReady:function(){ 
    // 页面渲染完成  
    var _this = this;  
    wx.getImageInfo({ 
      src: _this.data.tempFilePaths, 
      success: function (res) { 
        _this.setData({ 
          imgwidth:res.width, 
          imgheight:res.height, 
        }) 
      } 
    })  
  }  
}) 

<view class="zn-uploadimg"> 
  <button type="primary"bindtap="chooseimage">获取图片</button>  
  <image src="{{tempFilePaths}}" mode="aspecFill" style="width: 100%; height: 450rpx"/>  
  <text>图片的大小：{{imgwidth}}px*{{imgheight}}px</text> 
</view> 

.zn-uploadimg{ 
  padding:1rem; 
} 
.zn-uploadimg image{ 
  margin:1rem 0; 
}

var app = getApp()  
Page({ 
  data: {  
    tempFilePaths: '',  
    imgwidth:0, 
    imgheight:0, 
  }, 
  /**  
   * 上传图片 
   */ 
  chooseimage: function () {  
    var _this = this;  
    wx.chooseImage({  
      count: 1, // 默认9  
      sizeType: ['original', 'compressed'], // 可以指定是原图还是压缩图，默认二者都有  
      sourceType: ['album', 'camera'], // 可以指定来源是相册还是相机，默认二者都有  
      success: function (res) {  
        // 返回选定照片的本地文件路径列表，tempFilePath可以作为img标签的src属性显示图片  
        _this.setData({  
          tempFilePaths:res.tempFilePaths  
        })  
        wx.getImageInfo({ 
          src: res.tempFilePaths[0], 
          success: function (res) { 
            _this.setData({ 
              imgwidth:res.width, 
              imgheight:res.height, 
            }) 
          } 
        })  
      }  
    })  
  }  
})