微信小程序保存当前画布指定区域的内容导出生成指定大小的图片，记录一下
api：wx.canvasToTempFilePath
效果：
代码：wxml
<canvas style="width: {{screenWidth}}px; height: {{canvasHeight}}px;" canvas-id="myCanvas"></canvas><view class="bottom-btn"><van-button custom-class="info-sub" bind:tap="submit" block>下载图片</van-button></view>
js
onLoad(options) {this.initCanvas()
},
initCanvas(){// 自动计算收货地址高度，每一个收货地址占高度60，所以没加一条，高度+60let height = this.data.list.length <7?this.data.canvasHeight:this.data.canvasHeight + (this.data.list.length -6 )*60;console.log(height,'height');var ctx = wx.createCanvasContext('myCanvas')ctx.fillStyle = '#fff' // 背景色一定要设置，否则下载到图库中会有bugctx.fillRect( 0, 0, this.data.screenWidth, height) // 设置画布宽高ctx.setFillStyle('#333')ctx.setFontSize(13);ctx.setTextAlign('left');// 填充内容ctx.fillText('申请时间', 25, 65, 200, 30);ctx.fillText(this.data.time, 160, 65, 200, 30);ctx.fillText('会员ID', 25, 95, 200, 30);ctx.fillText(this.data.member, 160, 95, 200, 30);ctx.fillText('昵称', 25, 125, 200, 30);ctx.fillText(this.data.nickName, 160, 125, 200, 30);ctx.fillText('电话', 25, 155, 200, 30);ctx.fillText(this.data.mobile, 160, 155, 200, 30);ctx.setFontSize(15);ctx.setFillStyle('#333')ctx.fillText('配送地址：', 20, 195, 200, 30);ctx.setFillStyle('#333')ctx.setFontSize(11);// 地址是循环出来的，由于后端返回省市区是编号，我这边要转换for (var i = 0; i < this.data.list.length; i++) {let pro = seekProvince(this.data.list[i].province).namelet city = seekCity(this.data.list[i].city).namelet area = seekArea(this.data.list[i].area).namectx.fillText(pro+city+area, 25, 220+(i*60), 200, 30);ctx.fillText(this.data.list[i].addressDetail, 25, i==0?235:235+(i*60), 200, 30);ctx.fillText(this.data.list[i].memberName+' '+this.data.list[i].mobile, 25, i==0?250:250+(i*60), 200, 30);}let self = this// 这里需要注意，直接使用ctx.draw()，会提示我报错画布为空，将延迟期异步写到draw回调里，可以解决这个问题ctx.draw(false,async()=>{setTimeout(() => {wx.canvasToTempFilePath({x: 0,y: 0,width: self.data.screenWidth,height: self.data.canvasHeight,destWidth: self.data.screenWidth * 3,destHeight: self.data.canvasHeight * 3,canvasId: 'myCanvas',success(res) {self.setData({temp_path: res.tempFilePath})console.log(res.tempFilePath)},fail(err){console.log(err,'这是报错的');}},self)}, 100);})},
// 点击下载图片将画布内容下载到手机相册中
submit() {this.saveImgToAlbum()},saveImgToAlbum() {console.log(this.data.temp_path,'----')let self = thiswx.showLoading({title: '保存中...',icon: 'none'})setTimeout(()=>{wx.saveImageToPhotosAlbum({filePath: self.data.temp_path,success(res) {wx.hideLoading({success: (res) => {},})wx.showToast({title: '保存成功',icon: 'none'})},fail(res) {wx.hideLoading({success: (res) => {},})wx.showToast({title: '保存失败，请重新保存'+res.errMsg,icon: 'none'})console.log(res.errMsg)wx.getSetting({success(res) {if (!res.authSetting['scope.writePhotosAlbum']) {self.setData({showAuth: true})} else {self.setData({showAuth: false})}}})}})}, 1000) },
css部分就不写了，主要是底部按钮的样式，至此就完成啦！
