我想拖动节点并拖动画布（svg元素） 在桌面浏览器上，它工作正常，但在iPad上它只拖动画布;节点拖动无效。我哪里出错了？
我的源代码：
<!DOCTYPE html>
<meta charset="utf-8">
<style>
.node {
stroke: #fff;
stroke-width: 1.5px;
}
.link {
stroke: #999;
}
</style>
<body>
<script src="d3.js"></script>
<script>
var view_w = width = 960,
view_h = height = 500,
view_y = 0,
view_x = 0;
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.attr("viewBox", view_x+" "+view_y+" "+view_w+" "+view_h);
var canvasdrag = d3.behavior.drag().on("drag", function(d){
view_x -= d3.event.dx;
view_y -= d3.event.dy;
//change svg position
svg.attr("translate", view_x + " " + view_y);
//change viewBox start position
svg.attr("viewBox", view_x+" "+view_y+" "+view_w+" "+view_h);
});
svg.call(canvasdrag);
d3.json("./sample.json", function(error, graph) {
graph.links.forEach(function(d) {
d.source = graph.nodes[d.source];
d.target = graph.nodes[d.target];
});
var link = svg.append("g")
.attr("class", "link")
.selectAll("line")
.data(graph.links)
.enter().append("line")
.attr("x1", function(d) { return d.source.x; })
.attr("y1", function(d) { return d.source.y; })
.attr("x2", function(d) { return d.target.x; })
.attr("y2", function(d) { return d.target.y; });
var node = svg.append("g")
.attr("class", "node")
.selectAll("circle")
.data(graph.nodes)
.enter().append("circle")
.attr("r", 6)
.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; })
.call(d3.behavior.drag()
.origin(function(d) { return d; })
.on("drag", function(d) {
d.x = d3.event.x, d.y = d3.event.y;
d3.select(this).attr("cx", d.x).attr("cy", d.y);
link.filter(function(l) { return l.source === d; }).attr("x1", d.x).attr("y1", d.y);
link.filter(function(l) { return l.target === d; }).attr("x2", d.x).attr("y2", d.y);
}));
});
</script>
[sample.json]
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我正在使用d3.js版本788855b4a4141fab9554513976dcc50004c76489。