如何在 svg 到画布转换完成后立即发布？

Question

在将 html 元素中的所有 svg 转换为画布后，我正在尝试使用 html2canvas 发布，但该帖子在 svg 到画布转换完成之前立即执行，因为它需要几秒钟。我尝试过使用 deferred 和 Promise，但我仍然遇到同样的问题。

    // https://github.com/niklasvh/html2canvas/issues/95#issuecomment-45114424
    // First render all SVGs to canvases
    targetElem = $('#dashboard');

    var elements = targetElem.find('svg').map(function() {
        var svg = $(this);
        var canvas = $('<canvas></canvas>');
        svg.replaceWith(canvas);

        // Get the raw SVG string and curate it
        var content = svg.wrap('<p></p>').parent().html();
        content = content.replace(/xlink:title='hide\/show'/g, '');
        content = encodeURIComponent(content);
        svg.unwrap();

        // Create an image from the svg
        var image = new Image();
        image.src = 'data:image/svg+xml,' + content;
        image.onload = function() {
            canvas[0].width = image.width;
            canvas[0].height = image.height;

            // Render the image to the canvas
            var context = canvas[0].getContext('2d');
            context.drawImage(image, 0, 0);
        };

        return {
            svg: svg,
            canvas: canvas
        };
    }); // end of targetElem.find('svg').map(function() {...});

已编辑：这是我一直在尝试实现的延迟和承诺，以创建两个按顺序运行的操作。

$(document).ready(function() {

    $( '#save_dashboard' ).click(function() {

    // Create a deferred object
    var dfd = $.Deferred();

        // https://github.com/niklasvh/html2canvas/issues/95#issuecomment-45114424
        // First render all SVGs to canvases
        targetElem = $('#dashboard');

        var elements = targetElem.find('svg').map(function() {
            var svg = $(this);
            var canvas = $('<canvas></canvas>');
            svg.replaceWith(canvas);

            // Get the raw SVG string and curate it
            var content = svg.wrap('<p></p>').parent().html();
            content = content.replace(/xlink:title='hide\/show'/g, '');
            content = encodeURIComponent(content);
            svg.unwrap();

            // Create an image from the svg
            var image = new Image();
            image.src = 'data:image/svg+xml,' + content;
            image.onload = function() {
                canvas[0].width = image.width;
                canvas[0].height = image.height;

                // Render the image to the canvas
                var context = canvas[0].getContext('2d');
                context.drawImage(image, 0, 0);
            };
            dfd.resolve();

            return dfd.promise();
            };
        }); // end of targetElem.find('svg').map(function() {...});

        dfd.resolve();

        $.when(dfd).done(function(){
            console.log('dfd done');

            // http://www.kubilayerdogan.net/html2canvas-take-screenshot-of-web-page-and-save-it-to-server-javascript-and-php/
            $('#dashboard').html2canvas({
                onrendered: function (canvas) {
                    //Set hidden field's value to image data (base-64 string)
                    var dashboardPng = canvas.toDataURL('image/png');
                    console.log('dashboardPng: ' + dashboardPng);

                    $.ajax({
                        url:'save_dashboard_image.php',
                        data:{dashboardPngData: dashboardPng},
                        type:'POST',
                        dataType:'json',
                        success: function(){
                            console.log('success');
                        }
                        ,
                        error: function(xhr, status, error){
                            console.log('The requested page was: ' + document.URL +
                                '. The error number returned was: ' + xhr.status +
                                '. The error message was: ' + error);
                        }
                    });
                }
            });
        }); // end of $.when(dfd).done(...)
    }); // end of save_dashboard click function
}); // end of document ready

Answer 1

更新

注意，未经测试。调整click事件返回多个canvas，promise对象，到.then()

如果正确解释问题，请尝试

$(document).ready(function() {

    $( '#save_dashboard' ).click(function() {

    // Create a deferred object
    // dfd = new $.Deferred();

        // https://github.com/niklasvh/html2canvas/issues/95#issuecomment-45114424
        // First render all SVGs to canvases
        targetElem = $('#dashboard');
        var promises = $.when.apply(targetElem, $.map(targetElem.find('svg')
          , function(el, index) {
            return new $.Deferred(function(dfd) {
              var svg = $(el);
              var canvas = $('<canvas></canvas>');
              svg.replaceWith(canvas);

              // Get the raw SVG string and curate it
              var content = svg.wrap('<p></p>').parent().html();
              content = content.replace(/xlink:title='hide\/show'/g, '');
              content = encodeURIComponent(content);
              svg.unwrap();

              // Create an image from the svg
              var image = new Image();

              image.onload = function() {
                  canvas[0].width = image.width;
                  canvas[0].height = image.height;

                  // Render the image to the canvas
                  var context = canvas[0].getContext('2d');

                  dfd.resolve(context.drawImage(image, 0, 0));
              };
              image.src = 'data:image/svg+xml,' + content;
            }).promise();          
          })
         ); // end of targetElem.find('svg').map(function() {...});



        promises.then(function(_canvas) {
            console.log('dfd done', _canvas, arguments);

            // http://www.kubilayerdogan.net/html2canvas-take-screenshot-of-web-page-and-save-it-to-server-javascript-and-php/
            $('#dashboard').html2canvas({
                onrendered: function (canvas) {
                    //Set hidden field's value to image data (base-64 string)
                    var dashboardPng = canvas.toDataURL('image/png');
                    console.log('dashboardPng: ' + dashboardPng);

                    $.ajax({
                        url:'save_dashboard_image.php',
                        data:{dashboardPngData: dashboardPng},
                        type:'POST',
                        dataType:'json',
                        success: function(){
                            console.log('success');
                        }
                        ,
                        error: function(xhr, status, error){
                            console.log('The requested page was: ' + document.URL +
                                '. The error number returned was: ' + xhr.status +
                                '. The error message was: ' + error);
                        }
                    });
                }
            });
        }); // end of $.when(dfd).done(...)
    }); // end of save_dashboard click function
}); // end of document 

Answer 2

解决方案我必须为每个连续的 svg 到画布转换以及它们都完成时使用一个数组。我可以将数组传递给 then() 以发布 html2canvas。

1. 点击时创建一个新数组，用它来存储来自 SVG 的所有延迟
2. 循环遍历所有 SVG 元素
   • 在每个实例中，创建一个新的内部延迟对象
   • 解决或拒绝延期
   • 将其推入循环外的数组中

3. 使用$.when.apply($, arrayOfDeferredObjects) 检查数组中所有延迟对象的状态

   $( '#save_dashboard' ).click(function() {
   
       // Declare an array to store all deferred objects from each svg element
       var svgDfds = [],
           targetElem = $('#dashboard');
   
       targetElem.find('svg').each(function() {
           var dfd = new $.Deferred(),
               svg = $(this),
               canvas = $('<canvas></canvas>');
   
           svg.replaceWith(canvas);
   
           // Get the raw SVG string and curate it
           var content = svg.wrap('<p></p>').parent().html();
           content = content.replace(/xlink:title='hide\/show'/g, '');
           content = encodeURIComponent(content);
           svg.unwrap();
   
           // Create an image from the svg
           var image = new Image();
           image.src = 'data:image/svg+xml,' + content;
           image.onload = function() {
               canvas[0].width = image.width;
               canvas[0].height = image.height;
   
               // Render the image to the canvas
               var context = canvas[0].getContext('2d');
   
               // Resolve or reject the deferred
               dfd.resolve(context.drawImage(image, 0, 0));
           };
   
           // Push deferred object into array
           svgDfds.push(dfd);
   
       }); // end of targetElem.find('svg').map(function() {...});
   
       // Check for all deferreds
       $.when.apply($, svgDfds).then(function(_canvas) {
           console.log('dfd done', _canvas);
   
           // http://www.kubilayerdogan.net/html2canvas-take-screenshot-of-web-page-and-save-it-to-server-javascript-and-php/
           $('#dashboard').html2canvas({
               onrendered: function (canvas) {
                   //Set hidden field's value to image data (base-64 string)
                   var dashboardPng = canvas.toDataURL('image/png');
                   console.log('dashboardPng: ' + dashboardPng);
   
                   $.ajax({
                       url:'save_dashboard_image.php',
                       data:{dashboardPngData: dashboardPng},
                       type:'POST',
                       dataType:'json',
                       success: function(){
                           console.log('success');
                       }
                       ,
                       error: function(xhr, status, error){
                           console.log('The requested page was: ' + document.URL +
                               '. The error number returned was: ' + xhr.status +
                               '. The error message was: ' + error);
                       }
                   });
               }
           });
       });
   
   }); // end of save_dashboard click function