ios - 如何在 ios 图表中仅呈现选定的轴标签

Question

我正在使用的库:charts
我有一年中特定日期的折线图。我不想把每一天都画成 x 轴上的标签(可能有超过 300 天的范围)所以我只想画几个月。现在，我的 xVals 看起来像:[nil, nil, nil, "07/2016", nil nil nil (..)]。不幸的是，没有标签显示。
还有其他方法可以实现所需的行为吗？

代码(x轴值):

while date.compare(to) != NSComparisonResult.OrderedDescending { // iterate over all days in range
        let components = currentCalendar.components([.Day, .Month , .Year], fromDate: date)
        if components.day != 1 {
            vals.append(nil)
        } else { // first day of the month
            vals.append(String(components.month) + " / " + String(components.year))
        }

        let incrementComponents = NSDateComponents()
        incrementComponents.day = 1
        date = currentCalendar.dateByAddingComponents(incrementComponents, toDate: date, options: [])!
}

和条目:

for point in base!.points {
        if let index = chartValuesFormatter?.indexFromDate(point.date) {
            entries.append(ChartDataEntry(value: point.value, xIndex: index))
        }
}

通常它有效，当我指定所有值时，其中一些值会显示并且条目会正确呈现。我唯一的问题是在月初只显示月份标签。

Answer 1

好的，所以我找到了解决方案。它不像应该的那样简单(对于这样的基本问题)，但是非常可定制。 LineChartView(通过 BarLineChartViewBase) 具有属性 xAxisRenderer。您可以子类化默认的 ChartXAxisRenderer，并覆盖 drawLabels 函数。就我而言，我复制了原始代码并修改了计算应该绘制什么标签和绘制位置的逻辑。

编辑:我的带有重叠逻辑的自定义渲染器。可能过于复杂，但到目前为止它仍然有效。

class ChartXAxisDateRenderer: ChartXAxisRenderer {
internal static let FDEG2RAD = CGFloat(M_PI / 180.0)

/// draws the x-labels on the specified y-position
override func drawLabels(context context: CGContext, pos: CGFloat, anchor: CGPoint) {

    guard let xAxis = xAxis else { return }

    let paraStyle = NSParagraphStyle.defaultParagraphStyle().mutableCopy() as! NSMutableParagraphStyle
    paraStyle.alignment = .Center

    let labelAttrs = [NSFontAttributeName: xAxis.labelFont,
                      NSForegroundColorAttributeName: xAxis.labelTextColor,
                      NSParagraphStyleAttributeName: paraStyle]
    let labelRotationAngleRadians = xAxis.labelRotationAngle * ChartXAxisDateRenderer.FDEG2RAD

    let valueToPixelMatrix = transformer.valueToPixelMatrix

    let minLabelsMargin: CGFloat = 4.0

    var position = CGPoint(x: 0.0, y: 0.0)

    var labelMaxSize = CGSize()

    if (xAxis.isWordWrapEnabled) {
        labelMaxSize.width = xAxis.wordWrapWidthPercent * valueToPixelMatrix.a
    }

    var positions = [CGPoint]()
    var widths = [CGFloat]()
    var labels = [String]()
    var originalIndices = [Int]()

    for i in 0...xAxis.values.count-1 {
        let label = xAxis.values[i]
        if (label == nil || label == "")
        {
            continue
        }

        originalIndices.append(i)
        labels.append(label!)

        position.x = CGFloat(i)
        position.y = 0.0
        position = CGPointApplyAffineTransform(position, valueToPixelMatrix)
        positions.append(position)

        let labelns = label! as NSString
        let width = labelns.boundingRectWithSize(labelMaxSize, options: .UsesLineFragmentOrigin, attributes: labelAttrs, context: nil).size.width
        widths.append(width)
    }

    let newIndices = findBestPositions(positions, widths: widths, margin: minLabelsMargin)

    for index in newIndices {
        let label = labels[index]
        let position = positions[index]
        let i = originalIndices[index]

        if (viewPortHandler.isInBoundsX(position.x)) {
            drawLabel(context: context, label: label, xIndex: i, x: position.x, y: pos, attributes: labelAttrs, constrainedToSize: labelMaxSize, anchor: anchor, angleRadians: labelRotationAngleRadians)
        }
    }
}

// Best position indices - minimum "n" without overlapping
private func findBestPositions(positions: [CGPoint], widths: [CGFloat], margin: CGFloat) -> [Int] {
    var n = 1
    var overlap = true

    // finding "n"
    while n < widths.count && overlap {
        overlap = doesOverlap(n, positions: positions, widths: widths, margin: margin)
        if overlap {
            n += 1
        }
    }

    var newPositions = [Int]()
    var i = 0
    // create result indices
    while i < positions.count {
        newPositions.append(i)
        i += n
    }

    return newPositions
}

// returns whether drawing only n-th labels will casue overlapping
private func doesOverlap(n: Int, positions: [CGPoint], widths: [CGFloat], margin: CGFloat) -> Bool {
    var i = 0
    var newPositions = [CGPoint]()
    var newWidths = [CGFloat]()

    // getting only n-th records
    while i < positions.count {
        newPositions.append(positions[i])
        newWidths.append(widths[i])
        i += n
    }

    // overlap with next label checking
    for j in 0...newPositions.count - 2 {
        if newPositions[j].x + newWidths[j] + margin > newPositions[j+1].x {
            return true
        }
    }

    return false
}