d3：为什么此函数不能删除元素？

Question

Working in d3, I've got a function call that correctly draws a bar chart, but it doesn't update it correctly. Here's the important part of my code:

  # Drawing Elements
  @svg = d3.select(@s).append('svg').attr('width',@w).attr('height',@h)
  @rects = @svg.selectAll('rect')
  @labels = @svg.selectAll('text')

  drawRects: (data) ->
    rects = @rects.data(data)
    rects.enter().append('rect')
    rects.exit().remove()
    rects.attr('x', (d,i) => this.xScale(i) )
      .attr('y', (d) => @h - this.yScale(d) )
      .attr('width', @w / @data.length - @pad)
      .attr('height', (d) => this.yScale(d) )
      .attr('fill','#FFC05C')


  drawLabels: (data) ->
    labels = @labels.data(data)
    labels.enter().append('text')
    labels.exit().remove()
    labels.text( (d) -> d )
      .attr('text-anchor','middle')
      .attr('x', (d,i) => this.xScale(i) + ((@w / @data.length - @pad)/2) )
      .attr('y', (d) => @h - this.yScale(d) + 15 )
      .attr('fill','white')

  update: (data) ->
    this.drawRects(data)
    this.drawLabels(data)

When I initially set the graph I create some data (in this case an array of 20 numbers) and call the draw methods:

data = [1..20]
this.drawRects(data)
this.drawLabels(data)

The graphs are drawn correctly.

However, if these methods are called a second time, to update the data, the new data is placed in the DOM, but the old data is left behind as well, so it's just making a whole new set of elements.

What am I doing wrong here that's keeping .exit() from removing the old DOM elements?

Answer 1

You need to reselect the rect and text elements and assign them the new data:

drawRects: (data) ->
    rects = @svg.selectAll('rect').data(data)
    #...

drawLabels: (data) ->
    labels = @svg.selectAll('text').data(data)
    #...

In your code you always assign the new data to the old (empty) @rect and (empty) @labels collections. And the data will be treated as "entered" for these empty collections and thus new elements will be created and nothing will be removed.