.data() 处的 D3 新数据使 svg 重绘而不是更新节点位置

编程问答 2022-05-29

问题描述

考虑到这个工作 example，数据更新使 svg 更新而无需重新绘制。相关的原始代码部分，使其行为如解释：

// DATA JOIN
link = link.data(firstLinks ? graph.links1 : graph.links2);

// DATA JOIN
node = node.data(graph.nodes);

simulation.force("link")
    .links(firstLinks ? graph.links1 : graph.links2);

但是，如果节点和链接数据引用是新的，即使内容相同，svg 也会在每次更新时重新绘制。 相关的更改代码部分，使其行为如解释：

var new_graph_http_data = fetchNewData(); // unreferenced new data copy from graph

// DATA JOIN
link = link.data(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);

// DATA JOIN
node = node.data(new_graph_http_data.nodes);

simulation.force("link")
    .links(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);

Here，在函数 update() 中，调用 update_local() 将使图形按预期工作。调用 update_http() 将使图形重新绘制。

// Local working vs fetch (clone)
function update() {
    /* Original working version */
//  update_local();

    /* Re-drawing version */
    update_http();
};

update();
<!DOCTYPE html>
<html>
<Meta charset="UTF-8">
<style>
/*  Style DeFinitions  */
button {
  position: absolute;
  top: 1em;
  left: 1em;
}

.node {
    stroke: white;
    stroke-width: 2px;
}

.link {
    stroke: gray;
    stroke-width: 2px;
}

</style>
<button type="button" id="switch-btn">Switch Links</button>
<svg width="500" height="300"></svg>
<!--<script src="https://d3js.org/d3.v4.min.js"></script>-->
<script src="https://d3js.org/d3.v6.min.js"></script>
<script>
//  graph data store
// Part of original blocks-data.json
var graph = {
    "nodes": [
        { "id": "0","group": "1" },{ "id": "1","group": "2" },{ "id": "2",{ "id": "3",{ "id": "4",{ "id": "5","group": "3" },{ "id": "6",{ "id": "7",{ "id": "8","group": "3" }
    ],"links1": [
        { "source": "0","target": "1"},{ "source": "0","target": "2"},"target": "3"},"target": "4"},{ "source": "1","target": "5"},{ "source": "2","target": "6"},{ "source": "3","target": "7"},{ "source": "4","target": "8"},"target": "7"}
    ],"links2": [
        { "source": "0",{ "source": "5",{ "source": "7","target": "8"}
    ]
};

//  state variable for current link set
var firstLinks = true;

//  svg and sizing
var svg = d3.select("svg"),width = +svg.attr("width"),height = +svg.attr("height");

//  d3 color scheme
var color = d3.scaleOrdinal(d3.schemeCategory10);

// elements for data join
var link = svg.append("g").selectAll(".link"),node = svg.append("g").selectAll(".node");

//  simulation initialization
var simulation = d3.forceSimulation()
    .force("link",d3.forceLink()
        .id(function(d) { return d.id; }))
    .force("charge",d3.forceManyBody()
        .strength(function(d) { return -500;}))
    .force("center",d3.forceCenter(width / 2,height / 2));

//  button event handling
d3.select("#switch-btn").on("click",function() {
    firstLinks = !firstLinks;
    update();
});

//  follow v4 general update pattern
function update_local() {
    // Update link set based on current state
    // DATA JOIN
    link = link.data(firstLinks ? graph.links1 : graph.links2);
    
    // EXIT
    // Remove old links
    link.exit().remove();

    // ENTER
    // Create new links as needed.  
    link = link.enter().append("line")
        .attr("class","link")
        .merge(link);

    // DATA JOIN
    node = node.data(graph.nodes);

    // EXIT
    node.exit().remove();

    // ENTER
    node = node.enter().append("circle")
        .attr("class","node")
        .attr("r",10)
        .attr("fill",function(d) {return color(d.group);})
        .call(d3.drag()
          .on("start",dragstarted)
          .on("drag",dragged)
          .on("end",dragended)
        )
        .merge(node);

    //  Set nodes,links,and alpha target for simulation
    simulation
        .nodes(graph.nodes)
        .on("tick",ticked);

    simulation.force("link")
        .links(firstLinks ? graph.links1 : graph.links2);

    simulation.alphaTarget(0.3).restart();
}

//  follow v4 general update pattern
function update_http() {
    var new_graph_http_data = fetchNewData();
    // Update link set based on current state
    // DATA JOIN
    link = link.data(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);
    
    // EXIT
    // Remove old links
    link.exit().remove();

    // ENTER
    // Create new links as needed.  
    link = link.enter().append("line")
        .attr("class","link")
        .merge(link);

    // DATA JOIN
    node = node.data(new_graph_http_data.nodes);

    // EXIT
    node.exit().remove();

    // ENTER
    node = node.enter().append("circle")
        .attr("class",and alpha target for simulation
    simulation
        .nodes(new_graph_http_data.nodes)
        .on("tick",ticked);

    simulation.force("link")
        .links(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);

    simulation.alphaTarget(0.3).restart();
}

//  drag event handlers
function dragstarted(d) {
    if (!d3.event.active) simulation.alphaTarget(0.3).restart();
    d.fx = d.x;
    d.fy = d.y;
}

function dragged(d) {
    d.fx = d3.event.x;
    d.fy = d3.event.y;
}

function dragended(d) {
    if (!d3.event.active) simulation.alphaTarget(0);
    d.fx = null;
    d.fy = null;
}

//  tick event handler (nodes bound to container)
function ticked() {
    link
        .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; });

    node
        .attr("cx",function(d) { return d.x; })
        .attr("cy",function(d) { return d.y; });
}

// Value copying function
function fetchNewData() {
    var idx,tempStr;
    var obj = {
        "nodes": [],"links1": [],"links2": [],};

    for (idx in graph.nodes) {
        tempStr = JSON.stringify(graph.nodes[idx]);
        tempStr = JSON.parse(tempStr);
        obj.nodes.push(tempStr);
    }

    for (idx in graph.links1) {
        tempStr = JSON.stringify(graph.links1[idx]);
        tempStr = JSON.parse(tempStr);
        obj.links1.push(tempStr);
    }

    for (idx in graph.links2) {
        tempStr = JSON.stringify(graph.links2[idx]);
        tempStr = JSON.parse(tempStr);
        obj.links2.push(tempStr);
    }

    return obj;
}

</script>
</html>

在 Firefox 78.6.0esr 和 Chrome 86.0.4240.111 中使用 D3 v4.13.0 和 D3 v6.3.1 进行测试。开发工具不会抛出任何错误。

谢谢。

解决方法

虽然您关注的是进入/更新/退出循环，但问题在于 d3-force：代表节点的对象本身存储自己的位置数据。

D3-force 修改每个节点的数据以包含位置属性。这些属性是 tick 函数用来放置节点的：

node
    .attr("cx",function(d) { return d.x; })
    .attr("cy",function(d) { return d.y; });
})

除了 d.x 和 d.y，还有 d.vx 和 d.vy 属性。如果节点不具有这些属性，则力将创建并分配它们。如果删除所有节点并用没有 x,y 属性的新对象替换它们，则强制将创建和初始化这些属性而不考虑以前的节点（毕竟，它们不是不再进行模拟。从视觉上看，这将使所有旧节点/链接看起来都已退出，而新节点/链接已进入）。

如果您通过（重新）加载节点用新对象替换对象，并且新对象旨在位于旧节点所在的位置，则可以转移节点的x，y， dx,dy 属性，如果你想从旧节点到新对象，例如：

  var old = simulation.nodes()
  newGraph.nodes.forEach(function(node,i) {
       node.x = old[i].x;
       node.y = old[i].y;
       node.vx = old[i].vx;
       node.vy = old[i].vy;
  })

Update Fiddle

// Local working vs fetch (clone)
function update() {
    /* Original working version */
//  update_local();

    /* Re-drawing version */
    update_http();
};

update();
<!DOCTYPE html>
<html>
<meta charset="UTF-8">
<style>
/*  Style Definitions  */
button {
  position: absolute;
  top: 1em;
  left: 1em;
}

.node {
    stroke: white;
    stroke-width: 2px;
}

.link {
    stroke: gray;
    stroke-width: 2px;
}

</style>
<button type="button" id="switch-btn">Switch Links</button>
<svg width="500" height="300"></svg>
<!--<script src="https://d3js.org/d3.v4.min.js"></script>-->
<script src="https://d3js.org/d3.v6.min.js"></script>
<script>
//  graph data store
// Part of original blocks-data.json
var graph = {
    "nodes": [
        { "id": "0","group": "1" },{ "id": "1","group": "2" },{ "id": "2",{ "id": "3",{ "id": "4",{ "id": "5","group": "3" },{ "id": "6",{ "id": "7",{ "id": "8","group": "3" }
    ],"links1": [
        { "source": "0","target": "1"},{ "source": "0","target": "2"},"target": "3"},"target": "4"},{ "source": "1","target": "5"},{ "source": "2","target": "6"},{ "source": "3","target": "7"},{ "source": "4","target": "8"},"target": "7"}
    ],"links2": [
        { "source": "0",{ "source": "5",{ "source": "7","target": "8"}
    ]
};

//  state variable for current link set
var firstLinks = true;

//  svg and sizing
var svg = d3.select("svg"),width = +svg.attr("width"),height = +svg.attr("height");

//  d3 color scheme
var color = d3.scaleOrdinal(d3.schemeCategory10);

// elements for data join
var link = svg.append("g").selectAll(".link"),node = svg.append("g").selectAll(".node");

//  simulation initialization
var simulation = d3.forceSimulation()
    .force("link",d3.forceLink()
        .id(function(d) { return d.id; }))
    .force("charge",d3.forceManyBody()
        .strength(function(d) { return -500;}))
    .force("center",d3.forceCenter(width / 2,height / 2));

//  button event handling
d3.select("#switch-btn").on("click",function() {
    firstLinks = !firstLinks;
    update();
});

//  follow v4 general update pattern
function update_local() {
    // Update link set based on current state
    // DATA JOIN
    link = link.data(firstLinks ? graph.links1 : graph.links2);
    
    // EXIT
    // Remove old links
    link.exit().remove();

    // ENTER
    // Create new links as needed.  
    link = link.enter().append("line")
        .attr("class","link")
        .merge(link);

    // DATA JOIN
    node = node.data(graph.nodes);

    // EXIT
    node.exit().remove();

    // ENTER
    node = node.enter().append("circle")
        .attr("class","node")
        .attr("r",10)
        .attr("fill",function(d) {return color(d.group);})
        .call(d3.drag()
          .on("start",dragstarted)
          .on("drag",dragged)
          .on("end",dragended)
        )
        .merge(node);

    //  Set nodes,links,and alpha target for simulation
    simulation
        .nodes(graph.nodes)
        .on("tick",ticked);

    simulation.force("link")
        .links(firstLinks ? graph.links1 : graph.links2);

    simulation.alphaTarget(0.3).restart();
}

//  follow v4 general update pattern
function update_http() {
    var new_graph_http_data = fetchNewData();
    // Update link set based on current state
    // DATA JOIN
    link = link.data(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);
    
    // EXIT
    // Remove old links
    link.exit().remove();

    // ENTER
    // Create new links as needed.  
    link = link.enter().append("line")
        .attr("class","link")
        .merge(link);

    // DATA JOIN
    node = node.data(new_graph_http_data.nodes);

    // EXIT
    node.exit().remove();

    // ENTER
    node = node.enter().append("circle")
        .attr("class",and alpha target for simulation
    simulation
        .nodes(new_graph_http_data.nodes)
        .on("tick",ticked);

    simulation.force("link")
        .links(firstLinks ? new_graph_http_data.links1 : new_graph_http_data.links2);

    simulation.alphaTarget(0.3).restart();
}

//  drag event handlers
function dragstarted(d) {
    if (!d3.event.active) simulation.alphaTarget(0.3).restart();
    d.fx = d.x;
    d.fy = d.y;
}

function dragged(d) {
    d.fx = d3.event.x;
    d.fy = d3.event.y;
}

function dragended(d) {
    if (!d3.event.active) simulation.alphaTarget(0);
    d.fx = null;
    d.fy = null;
}

//  tick event handler (nodes bound to container)
function ticked() {
    link
        .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; });

    node
        .attr("cx",function(d) { return d.x; })
        .attr("cy",function(d) { return d.y; });
}

// Value copying function
function fetchNewData() {
  var idx,tempStr;
    var obj = {
        "nodes": [],"links1": [],"links2": [],};

    for (idx in graph.nodes) {
        tempStr = JSON.stringify(graph.nodes[idx]);
        tempStr = JSON.parse(tempStr);
        obj.nodes.push(tempStr);
    }

    for (idx in graph.links1) {
        tempStr = JSON.stringify(graph.links1[idx]);
        tempStr = JSON.parse(tempStr);
        obj.links1.push(tempStr);
    }

    for (idx in graph.links2) {
        tempStr = JSON.stringify(graph.links2[idx]);
        tempStr = JSON.parse(tempStr);
        obj.links2.push(tempStr);
    }
  
  if(simulation.nodes().length) {
  var old = simulation.nodes()
  obj.nodes.forEach(function(node,i) {
       node.x = old[i].x;
       node.y = old[i].y;
       node.vx = old[i].vx;
       node.vy = old[i].vy;
  })
  }
  

    return obj;
}

</script>
</html>

force-layoutjavascript