话说，2020年刚来杭州的时候，有用到过uniapp，距今已有三年时间了，果然全忘了，哈哈[笑中带泪]

昨天遇到一个需求：就是要实现pdf文件的预览，着实费了我很多的时间，连晚饭都没有吃好。。。

先写一个小的功能点记录：文档预览功能的实现——openDocument

放弃web-view

预览pdf我先是考虑了web-view组件，因为我有文档的链接，然后通过web-view中的src属性链接文档，然后实现的文档的预览。web端是没啥问题的，但是在手机端打开h5网页的时候，会出现空白页且退回时，直接无法退回的情况。

放弃iframe

接着，我又考虑了一下iframe组件，通过给src属性链接文档的形式来展示，但是在web端没啥问题，但是手机端会直接下载文档，而不是预览。放弃iframe

最后，咨询了黄河爱浪大神，黄河爱浪大神的博客地址：https://blog.csdn.net/u013350495?type=blog

决定用uni.openDocument来实现pdf的预览功能。

但是这个api的弊端正如上图所示：

pdf预览的效果:
在web端和vivo 小米的h5端，可以预览pdf，但是会有下载文件的提示，不影响预览，用华为，直接提示下载，没有预览功能。这个兼容性不是太好

其他人的写法——没有进行测试哈

uni.downloadFile({url: 'https://cdn.zhoukaiwen.com/kevin.pdf',success: function(res) {var filePath = res.tempFilePath;uni.openDocument({filePath: filePath,success: function(res) {console.log('打开文档成功');}});}
})

先通过uni.downloadFile的方式拿到文档链接对应的文件临时地址tempFilePath，然后再通过uni.openDocument的形式来预览。不知道这样的话，会不会就不出现下载的提示了。。。。

电子签名功能

直接上效果图：

上代码了：

html部分代码

<template><view><view class="wrapper"><view class="handBtn"><image @click="selectColorEvent('black','#1A1A1A')" :src="selectColor === 'black' ? '../static/other/color_black_selected.png' : '../static/other/color_black.png'":class="[selectColor === 'black' ? 'color_select' : '', 'black-select']"></image><image @click="selectColorEvent('red','#ca262a')" :src="selectColor === 'red' ? '../static/other/color_red_selected.png' : '../static/other/color_red.png'":class="[selectColor === 'red' ? 'color_select' : '', 'black-select']"></image><button @click="retDraw" class="delBtn">重写</button><button @click="saveCanvasAsImg" class="saveBtn">保存</button><button @click="previewCanvasImg" class="previewBtn">预览</button><button @click="uploadCanvasImg" class="uploadBtn">上传</button><button @click="subCanvas" class="subBtn">完成</button></view><view class="handCenter"><canvas class="handWriting" :disable-scroll="true" @touchstart="uploadScaleStart" @touchmove="uploadScaleMove"@touchend="uploadScaleEnd" canvas-id="handWriting"></canvas></view><view class="handRight"><view class="handTitle">请签名</view></view></view></view>
</template>

js部分代码

<script>export default {data() {return {canvasName: 'handWriting',ctx: '',canvasWidth: 0,canvasHeight: 0,transparent: 1, // 透明度selectColor: 'black',lineColor: '#1A1A1A', // 颜色lineSize: 1.5, // 笔记倍数lineMin: 0.5, // 最小笔画半径lineMax: 4, // 最大笔画半径pressure: 1, // 默认压力smoothness: 60, //顺滑度，用60的距离来计算速度currentPoint: {},currentLine: [], // 当前线条firstTouch: true, // 第一次触发radius: 1, //画圆的半径cutArea: {top: 0,right: 0,bottom: 0,left: 0}, //裁剪区域bethelPoint: [], //保存所有线条 生成的贝塞尔点；lastPoint: 0,chirography: [], //笔迹currentChirography: {}, //当前笔迹linePrack: [] //划线轨迹 , 生成线条的实际点};},onLoad() {let canvasName = this.canvasName;let ctx = wx.createCanvasContext(canvasName);this.ctx = ctx;var query = wx.createSelectorQuery();query.select('.handCenter').boundingClientRect(rect => {this.canvasWidth = rect.width;this.canvasHeight = rect.height;/* 将canvas背景设置为 白底，不设置  导出的canvas的背景为透明 */this.setCanvasBg('#fff');}).exec();},methods: {// 笔迹开始uploadScaleStart(e) {if (e.type != 'touchstart') return false;let ctx = this.ctx;ctx.setFillStyle(this.lineColor); // 初始线条设置颜色ctx.setGlobalAlpha(this.transparent); // 设置半透明let currentPoint = {x: e.touches[0].x,y: e.touches[0].y};let currentLine = this.currentLine;currentLine.unshift({time: new Date().getTime(),dis: 0,x: currentPoint.x,y: currentPoint.y});this.currentPoint = currentPoint;// currentLineif (this.firstTouch) {this.cutArea = {top: currentPoint.y,right: currentPoint.x,bottom: currentPoint.y,left: currentPoint.x};this.firstTouch = false;}this.pointToLine(currentLine);},// 笔迹移动uploadScaleMove(e) {if (e.type != 'touchmove') return false;if (e.cancelable) {// 判断默认行为是否已经被禁用if (!e.defaultPrevented) {e.preventDefault();}}let point = {x: e.touches[0].x,y: e.touches[0].y};//测试裁剪if (point.y < this.cutArea.top) {this.cutArea.top = point.y;}if (point.y < 0) this.cutArea.top = 0;if (point.x > this.cutArea.right) {this.cutArea.right = point.x;}if (this.canvasWidth - point.x <= 0) {this.cutArea.right = this.canvasWidth;}if (point.y > this.cutArea.bottom) {this.cutArea.bottom = point.y;}if (this.canvasHeight - point.y <= 0) {this.cutArea.bottom = this.canvasHeight;}if (point.x < this.cutArea.left) {this.cutArea.left = point.x;}if (point.x < 0) this.cutArea.left = 0;this.lastPoint = this.currentPoint;this.currentPoint = point;let currentLine = this.currentLine;currentLine.unshift({time: new Date().getTime(),dis: this.distance(this.currentPoint, this.lastPoint),x: point.x,y: point.y});this.pointToLine(currentLine);},// 笔迹结束uploadScaleEnd(e) {if (e.type != 'touchend') return 0;let point = {x: e.changedTouches[0].x,y: e.changedTouches[0].y};this.lastPoint = this.currentPoint;this.currentPoint = point;let currentLine = this.currentLine;currentLine.unshift({time: new Date().getTime(),dis: this.distance(this.currentPoint, this.lastPoint),x: point.x,y: point.y});if (currentLine.length > 2) {var info = (currentLine[0].time - currentLine[currentLine.length - 1].time) / currentLine.length;//$("#info").text(info.toFixed(2));}//一笔结束，保存笔迹的坐标点，清空，当前笔迹//增加判断是否在手写区域；this.pointToLine(currentLine);var currentChirography = {lineSize: this.lineSize,lineColor: this.lineColor};var chirography = this.chirography;chirography.unshift(currentChirography);this.chirography = chirography;var linePrack = this.linePrack;linePrack.unshift(this.currentLine);this.linePrack = linePrack;this.currentLine = [];},retDraw() {this.ctx.clearRect(0, 0, 700, 730);this.ctx.draw();//设置canvas背景this.setCanvasBg('#fff');},//画两点之间的线条；参数为:line，会绘制最近的开始的两个点；pointToLine(line) {this.calcBethelLine(line);return;},//计算插值的方式；calcBethelLine(line) {if (line.length <= 1) {line[0].r = this.radius;return;}let x0,x1,x2,y0,y1,y2,r0,r1,r2,len,lastRadius,dis = 0,time = 0,curveValue = 0.5;if (line.length <= 2) {x0 = line[1].x;y0 = line[1].y;x2 = line[1].x + (line[0].x - line[1].x) * curveValue;y2 = line[1].y + (line[0].y - line[1].y) * curveValue;//x2 = line[1].x;//y2 = line[1].y;x1 = x0 + (x2 - x0) * curveValue;y1 = y0 + (y2 - y0) * curveValue;} else {x0 = line[2].x + (line[1].x - line[2].x) * curveValue;y0 = line[2].y + (line[1].y - line[2].y) * curveValue;x1 = line[1].x;y1 = line[1].y;x2 = x1 + (line[0].x - x1) * curveValue;y2 = y1 + (line[0].y - y1) * curveValue;}//从计算公式看，三个点分别是(x0,y0),(x1,y1),(x2,y2) ；(x1,y1)这个是控制点，控制点不会落在曲线上；实际上，这个点还会手写获取的实际点，却落在曲线上len = this.distance({x: x2,y: y2}, {x: x0,y: y0});lastRadius = this.radius;for (let n = 0; n < line.length - 1; n++) {dis += line[n].dis;time += line[n].time - line[n + 1].time;if (dis > this.smoothness) break;}this.radius = Math.min((time / len) * this.pressure + this.lineMin, this.lineMax) * this.lineSize;line[0].r = this.radius;//计算笔迹半径；if (line.length <= 2) {r0 = (lastRadius + this.radius) / 2;r1 = r0;r2 = r1;//return;} else {r0 = (line[2].r + line[1].r) / 2;r1 = line[1].r;r2 = (line[1].r + line[0].r) / 2;}let n = 5;let point = [];for (let i = 0; i < n; i++) {let t = i / (n - 1);let x = (1 - t) * (1 - t) * x0 + 2 * t * (1 - t) * x1 + t * t * x2;let y = (1 - t) * (1 - t) * y0 + 2 * t * (1 - t) * y1 + t * t * y2;let r = lastRadius + ((this.radius - lastRadius) / n) * i;point.push({x: x,y: y,r: r});if (point.length == 3) {let a = this.ctaCalc(point[0].x, point[0].y, point[0].r, point[1].x, point[1].y, point[1].r, point[2].x, point[2].y, point[2].r);a[0].color = this.lineColor;// let bethelPoint = this.bethelPoint;// bethelPoint = bethelPoint.push(a);this.bethelDraw(a, 1);point = [{x: x,y: y,r: r}];}}this.currentLine = line;},//求两点之间距离distance(a, b) {let x = b.x - a.x;let y = b.y - a.y;return Math.sqrt(x * x + y * y);},ctaCalc(x0, y0, r0, x1, y1, r1, x2, y2, r2) {let a = [],vx01,vy01,norm,n_x0,n_y0,vx21,vy21,n_x2,n_y2;vx01 = x1 - x0;vy01 = y1 - y0;norm = Math.sqrt(vx01 * vx01 + vy01 * vy01 + 0.0001) * 2;vx01 = (vx01 / norm) * r0;vy01 = (vy01 / norm) * r0;n_x0 = vy01;n_y0 = -vx01;vx21 = x1 - x2;vy21 = y1 - y2;norm = Math.sqrt(vx21 * vx21 + vy21 * vy21 + 0.0001) * 2;vx21 = (vx21 / norm) * r2;vy21 = (vy21 / norm) * r2;n_x2 = -vy21;n_y2 = vx21;a.push({mx: x0 + n_x0,my: y0 + n_y0,color: '#1A1A1A'});a.push({c1x: x1 + n_x0,c1y: y1 + n_y0,c2x: x1 + n_x2,c2y: y1 + n_y2,ex: x2 + n_x2,ey: y2 + n_y2});a.push({c1x: x2 + n_x2 - vx21,c1y: y2 + n_y2 - vy21,c2x: x2 - n_x2 - vx21,c2y: y2 - n_y2 - vy21,ex: x2 - n_x2,ey: y2 - n_y2});a.push({c1x: x1 - n_x2,c1y: y1 - n_y2,c2x: x1 - n_x0,c2y: y1 - n_y0,ex: x0 - n_x0,ey: y0 - n_y0});a.push({c1x: x0 - n_x0 - vx01,c1y: y0 - n_y0 - vy01,c2x: x0 + n_x0 - vx01,c2y: y0 + n_y0 - vy01,ex: x0 + n_x0,ey: y0 + n_y0});a[0].mx = a[0].mx.toFixed(1);a[0].mx = parseFloat(a[0].mx);a[0].my = a[0].my.toFixed(1);a[0].my = parseFloat(a[0].my);for (let i = 1; i < a.length; i++) {a[i].c1x = a[i].c1x.toFixed(1);a[i].c1x = parseFloat(a[i].c1x);a[i].c1y = a[i].c1y.toFixed(1);a[i].c1y = parseFloat(a[i].c1y);a[i].c2x = a[i].c2x.toFixed(1);a[i].c2x = parseFloat(a[i].c2x);a[i].c2y = a[i].c2y.toFixed(1);a[i].c2y = parseFloat(a[i].c2y);a[i].ex = a[i].ex.toFixed(1);a[i].ex = parseFloat(a[i].ex);a[i].ey = a[i].ey.toFixed(1);a[i].ey = parseFloat(a[i].ey);}return a;},bethelDraw(point, is_fill, color) {let ctx = this.ctx;ctx.beginPath();ctx.moveTo(point[0].mx, point[0].my);if (undefined != color) {ctx.setFillStyle(color);ctx.setStrokeStyle(color);} else {ctx.setFillStyle(point[0].color);ctx.setStrokeStyle(point[0].color);}for (let i = 1; i < point.length; i++) {ctx.bezierCurveTo(point[i].c1x, point[i].c1y, point[i].c2x, point[i].c2y, point[i].ex, point[i].ey);}ctx.stroke();if (undefined != is_fill) {ctx.fill(); //填充图形 ( 后绘制的图形会覆盖前面的图形, 绘制时注意先后顺序 )}ctx.draw(true);},selectColorEvent(str, color) {this.selectColor = str;this.lineColor = color;},//将Canvas内容转成 临时图片 --> cb 为回调函数 形参 tempImgPath 为 生成的图片临时路径canvasToImg(cb) {//这种写法移动端 出不来this.ctx.draw(true, () => {wx.canvasToTempFilePath({canvasId: 'handWriting',fileType: 'png',quality: 1, //图片质量success(res) {// console.log(res.tempFilePath, 'canvas生成图片地址');wx.showToast({title: '执行了吗？'});cb(res.tempFilePath);}});});},//完成subCanvas() {this.ctx.draw(true, () => {wx.canvasToTempFilePath({canvasId: 'handWriting',fileType: 'png',quality: 1, //图片质量success(res) {// console.log(res.tempFilePath, 'canvas生成图片地址');wx.showToast({title: '以保存'});//保存到系统相册wx.saveImageToPhotosAlbum({filePath: res.tempFilePath,success(res) {wx.showToast({title: '已成功保存到相册',duration: 2000});}});}});});},//保存到相册saveCanvasAsImg() {/*this.canvasToImg( tempImgPath=>{// console.log(tempImgPath, '临时路径');wx.saveImageToPhotosAlbum({filePath: tempImgPath,success(res) {wx.showToast({title: '已保存到相册',duration: 2000});}})} );*/wx.canvasToTempFilePath({canvasId: 'handWriting',fileType: 'png',quality: 1, //图片质量success(res) {// console.log(res.tempFilePath, 'canvas生成图片地址');wx.saveImageToPhotosAlbum({filePath: res.tempFilePath,success(res) {wx.showToast({title: '已保存到相册',duration: 2000});}});}});},//预览previewCanvasImg() {wx.canvasToTempFilePath({canvasId: 'handWriting',fileType: 'jpg',quality: 1, //图片质量success(res) {// console.log(res.tempFilePath, 'canvas生成图片地址');wx.previewImage({urls: [res.tempFilePath] //预览图片 数组});}});/*	//移动端出不来  ^~^！！this.canvasToImg( tempImgPath=>{wx.previewImage({urls: [tempImgPath], //预览图片 数组})} );*/},//上传uploadCanvasImg() {wx.canvasToTempFilePath({canvasId: 'handWriting',fileType: 'png',quality: 1, //图片质量success(res) {// console.log(res.tempFilePath, 'canvas生成图片地址');//上传wx.uploadFile({url: 'https://example.weixin.qq.com/upload', // 仅为示例，非真实的接口地址filePath: res.tempFilePath,name: 'file_signature',formData: {user: 'test'},success(res) {const data = res.data;// do something}});}});},//设置canvas背景色  不设置  导出的canvas的背景为透明//@params：字符串  colorsetCanvasBg(color) {/* 将canvas背景设置为 白底，不设置  导出的canvas的背景为透明 *///rect() 参数说明  矩形路径左上角的横坐标，左上角的纵坐标, 矩形路径的宽度, 矩形路径的高度//这里是 canvasHeight - 4 是因为下边盖住边框了，所以手动减了写this.ctx.rect(0, 0, this.canvasWidth, this.canvasHeight - 4);// ctx.setFillStyle('red')this.ctx.setFillStyle(color);this.ctx.fill(); //设置填充this.ctx.draw(); //开画}}};
</script>

wx.createCanvasContext——用于创建一个canvas绘图上下文对象

wx.createCanvasContext是一个微信小程序API，用于创建一个canvas绘图上下文对象。通过该对象，可以进行canvas绘图操作，例如绘制图形、文字、图片等。在小程序中，可以使用该API来实现一些复杂的图形绘制和动画效果。

wx.createSelectorQuery——获取SelectorQuery 对象实例

获取SelectorQuery 对象实例
var query = wx.createSelectorQuery() //返回一个SelectorQuery 对象实例
使用SelectorQuery 对象方法如：
var nodesRef= query.select(“#my”) //返回一个NodesRef 对象实例

wx.canvasToTempFilePath——把当前画布指定区域的内容导出生成指定大小的图片

wx.canvasToTempFilePath(Object object, Object this)
把当前画布指定区域的内容导出生成指定大小的图片。在 draw() 回调里调用该方法才能保证图片导出成功。

wx.showToast——提示信息

wx.saveImageToPhotosAlbum——保存到系统相册

小程序保存图片到系统相册wx.saveImageToPhotosAlbum

wx.previewImage——预览图片

wx.uploadFile——上传文件

css代码

<style>page {background: #fbfbfb;height: auto;overflow: hidden;}.wrapper {width: 100%;height: 95vh;margin: 30rpx 0;overflow: hidden;display: flex;align-content: center;flex-direction: row;justify-content: center;font-size: 28rpx;}.handWriting {background: #fff;width: 100%;height: 95vh;}.handRight {display: inline-flex;align-items: center;}.handCenter {border: 4rpx dashed #e9e9e9;flex: 5;overflow: hidden;box-sizing: border-box;}.handTitle {transform: rotate(90deg);flex: 1;color: #666;}.handBtn button {font-size: 28rpx;}.handBtn {height: 95vh;display: inline-flex;flex-direction: column;justify-content: space-between;align-content: space-between;flex: 1;}.delBtn {position: absolute;top: 250rpx;left: 0rpx;transform: rotate(90deg);color: #666;}.delBtn image {position: absolute;top: 13rpx;left: 25rpx;}.subBtn {position: absolute;bottom: 52rpx;left: -3rpx;display: inline-flex;transform: rotate(90deg);background: #008ef6;color: #fff;margin-bottom: 30rpx;text-align: center;justify-content: center;}/*Peach - 新增 - 保存*/.saveBtn {position: absolute;top: 375rpx;left: 0rpx;transform: rotate(90deg);color: #666;}.previewBtn {position: absolute;top: 500rpx;left: 0rpx;transform: rotate(90deg);color: #666;}.uploadBtn {position: absolute;top: 625rpx;left: 0rpx;transform: rotate(90deg);color: #666;}/*Peach - 新增 - 保存*/.black-select {width: 60rpx;height: 60rpx;position: absolute;top: 30rpx;left: 25rpx;}.black-select.color_select {width: 90rpx;height: 90rpx;top: 100rpx;left: 10rpx;}.red-select {width: 60rpx;height: 60rpx;position: absolute;top: 140rpx;left: 25rpx;}.red-select.color_select {width: 90rpx;height: 90rpx;top: 120rpx;left: 10rpx;}
</style>

完成！！！多多积累，多多收获！！！