<view class="previewImage" style="display:{{previewImage}}" bindtap="closePrev">

    <image src="{{img.url}}" mode="aspectFit" style="width:100%;height:100%;" catchlongtap="saveImg"></image>

</view>

<action-sheet hidden="{{saveImage}}" bindchange="actionSheetChange">

    <block>

        <action-sheet-item class="item" bindtap="downloadFile" data-image-href="{{img.url}}">保存图片</action-sheet-item>

    </block>

    <action-sheet-cancel class="cancel">取消</action-sheet-cancel>

</action-sheet>

.previewImage{

    position: absolute;

    top:;

    left:;

    width: 100%;

    height: 100%;

    background-color: #000;

}

    previewImg:function(){

        this.setData({

            previewImage:"block"

        });

    },

    saveImg:function(){

        longTouch = true;

        this.setData({

            saveImage:false

        })

    },

    closePrev:function(){

        if(longTouch){

            longTouch = false;

        }else{

            this.setData({

                previewImage:"none"

            });

        }

    },

    actionSheetChange:function(){

        this.setData({

            saveImage:!this.data.saveImage

        })

    },

    downloadFile:function(e){

        var imgUrl = e.currentTarget.dataset.imageHref;

        var that = this;

        wx.downloadFile({

              url: imgUrl,

              type: 'image',

              success:function(res){

                  var tempFilePath = res.tempFilePath;

                console.log(tempFilePath);

                wx.saveFile({

                      tempFilePath:tempFilePath,

                      success:function(res){

                        var savedFilePath = res.savedFilePath;

                        console.log(savedFilePath);

                        that.setData({

                            saveImage:true

                        });

                      },

                      fail:function(res){

                          console.log(res);

                      }

                });

              },

              fail:function(res){

                  console.log(res);

              }

        });

    }