.data() 中的 D3 新数据使 svg 重绘而不是更新节点位置

D3 new data at .data() makes svg to redraw instead of updating nodes position

考虑到此工作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它的行为如所解释的那样：

// 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，每次更新都会重新绘制 svg。 相关更改的代码部分使它的行为如解释的那样：

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", "group": "2" },
        { "id": "3", "group": "2" },
        { "id": "4", "group": "2" },
        { "id": "5", "group": "3" },
        { "id": "6", "group": "3" },
        { "id": "7", "group": "3" },
        { "id": "8", "group": "3" }
    ],
    "links1": [
        { "source": "0", "target": "1"},
        { "source": "0", "target": "2"},
        { "source": "0", "target": "3"},
        { "source": "0", "target": "4"},
        { "source": "1", "target": "5"},
        { "source": "2", "target": "6"},
        { "source": "3", "target": "7"},
        { "source": "4", "target": "8"},
        { "source": "1", "target": "8"},
        { "source": "2", "target": "5"},
        { "source": "3", "target": "6"},
        { "source": "4", "target": "7"}
    ],
    "links2": [
        { "source": "0", "target": "5"},
        { "source": "0", "target": "6"},
        { "source": "0", "target": "7"},
        { "source": "0", "target": "8"},
        { "source": "5", "target": "6"},
        { "source": "5", "target": "8"},
        { "source": "7", "target": "6"},
        { "source": "7", "target": "8"},
        { "source": "1", "target": "5"},
        { "source": "2", "target": "6"},
        { "source": "3", "target": "7"},
        { "source": "4", "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", "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(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 进行了测试。开发工具上没有错误。

谢谢。

虽然您关注的是 enter/update/exit 循环，但问题在于 d3-force：代表节点的对象本身存储了它们自己的位置数据。

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属性：

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。如果一个节点没有这些属性，力将创建并分配它们。如果您删除所有节点并用没有 x,y 属性的新对象替换它们，力将创建和初始化这些属性而不考虑以前的节点（毕竟，它们不是不再模拟。在视觉上，这将使它看起来像所有旧的 nodes/links 已退出并进入新的）。

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", "group": "2" },
        { "id": "3", "group": "2" },
        { "id": "4", "group": "2" },
        { "id": "5", "group": "3" },
        { "id": "6", "group": "3" },
        { "id": "7", "group": "3" },
        { "id": "8", "group": "3" }
    ],
    "links1": [
        { "source": "0", "target": "1"},
        { "source": "0", "target": "2"},
        { "source": "0", "target": "3"},
        { "source": "0", "target": "4"},
        { "source": "1", "target": "5"},
        { "source": "2", "target": "6"},
        { "source": "3", "target": "7"},
        { "source": "4", "target": "8"},
        { "source": "1", "target": "8"},
        { "source": "2", "target": "5"},
        { "source": "3", "target": "6"},
        { "source": "4", "target": "7"}
    ],
    "links2": [
        { "source": "0", "target": "5"},
        { "source": "0", "target": "6"},
        { "source": "0", "target": "7"},
        { "source": "0", "target": "8"},
        { "source": "5", "target": "6"},
        { "source": "5", "target": "8"},
        { "source": "7", "target": "6"},
        { "source": "7", "target": "8"},
        { "source": "1", "target": "5"},
        { "source": "2", "target": "6"},
        { "source": "3", "target": "7"},
        { "source": "4", "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", "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(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>