如何使用ios-charts库在烛台图表中创建自定义限制线标签？

Question

我正在使用“图表”库在我的iOS应用程序中绘制烛台图表。

如何在限制线上贴标签，如下图所示？

Example

据我所知，我必须为Y轴创建自定义渲染器并覆盖绘制限制线和/或Y轴标签的方法。到目前为止，我设法实现了这个screenshot，但标签没有附加到限制线的右端并且具有静态位置，这意味着如果我缩放或拖动图表它不能正确移动轴上的其他标签。截至目前，Y标签由图表自动生成。

我试着按照这个例子，但它对我不起作用：Custom view of Limit Line in MPAndroidChart

你能告诉我到底要做什么来制作限制线，它的标签在示例图像上看起来像什么？因为我是iOS编程的新手，所以有一个详细的解释+代码会很高兴。

Answer 1

好吧，所以在对Y轴渲染器进行一些修补之后，我设法实现了这种外观和行为。

因此，为了获得这种外观，您必须：

1. 通过调用setDrawLabelsEnabled()并将参数设置为false来禁用默认限制线标签
2. 对YAxisRenderer.swift进行更改。关键是稍微重做internal func drawYLabels(...)以为每个限制线绘制额外的标签。请参阅下面的代码。
3. 将偏移量添加到X和Y轴（两者），如下所示：

   chart.leftAxis.xOffset = 10.0
    chart.leftAxis.yOffset = 0.0

这是新的internal func drawYLabels(...)方法的代码片段：

internal func drawYLabels(
        context: CGContext,
        fixedPosition: CGFloat,
        positions: [CGPoint],
        offset: CGFloat,
        textAlign: NSTextAlignment)
    {
        guard
            let yAxis = self.axis as? YAxis
            else { return }

        let labelFont = yAxis.labelFont
        let labelTextColor = yAxis.labelTextColor

        let from = yAxis.isDrawBottomYLabelEntryEnabled ? 0 : 1
        let to = yAxis.isDrawTopYLabelEntryEnabled ? yAxis.entryCount : (yAxis.entryCount - 1)

        for i in stride(from: from, to: to, by: 1)
        {
            let text = yAxis.getFormattedLabel(i)

            ChartUtils.drawText(
                context: context,
                text: "   " + text + "   ",     // Adding some spaces infront and after the label to make some additional space for the bigger "limit line" labels
                point: CGPoint(x: fixedPosition, y: positions[i].y + offset),
                align: textAlign,
                attributes: [NSAttributedString.Key.font: labelFont, NSAttributedString.Key.foregroundColor: labelTextColor])


        }

        // This is where we start to draw labels for limit lines
        let myTransformer = self.transformer

        for line in yAxis.limitLines {

            let point = myTransformer!.pixelForValues(x: 0.0, y: line.limit)

            let text = ("  " + line.label + "  ") as NSString       // Adding some spaces to the label in order to make some additional space for the label
            let size = text.size(withAttributes: [NSAttributedString.Key.font: labelFont, NSAttributedString.Key.foregroundColor: UIColor.darkGray, NSAttributedString.Key.backgroundColor: UIColor.green])
            var labelPoint: CGPoint?

            // Drawing the triangle in front of the custom label
            let trianglePath = UIBezierPath()
            if yAxis.axisDependency == .right {
                labelPoint = CGPoint(x: fixedPosition + (size.height * 0.3), y: point.y - (size.height / 2))

                if textAlign == .center
                {
                    labelPoint!.x -= size.width / 2.0
                }
                else if textAlign == .right
                {
                    labelPoint!.x -= size.width
                }



                trianglePath.move(to: CGPoint(x: labelPoint!.x - size.height * 0.375, y: labelPoint!.y + (size.height / 2)))
                trianglePath.addLine(to: CGPoint(x: labelPoint!.x, y: labelPoint!.y + (size.height * 0.78)))
                trianglePath.addLine(to: CGPoint(x: labelPoint!.x, y: labelPoint!.y + (size.height * 0.22)))

            } else {

                labelPoint = CGPoint(x: 0.0, y: point.y - (size.height / 2))

                trianglePath.move(to: CGPoint(x: labelPoint!.x + size.width * 1.175, y: labelPoint!.y + (size.height / 2)))
                trianglePath.addLine(to: CGPoint(x: labelPoint!.x + size.width, y: labelPoint!.y + (size.height * 0.78)))
                trianglePath.addLine(to: CGPoint(x: labelPoint!.x + size.width, y: labelPoint!.y + (size.height * 0.22)))
            }

            NSUIGraphicsPushContext(context)

            // Drawing the custom label itself
            (text as NSString).draw(at: labelPoint!, withAttributes: [NSAttributedString.Key.font: labelFont, NSAttributedString.Key.foregroundColor: UIColor.darkGray, NSAttributedString.Key.backgroundColor: UIColor.green])

            trianglePath.close()

            // Drawing the triangle with the same color as the limit line and it's label
            line.lineColor.setFill()
            trianglePath.fill()

            NSUIGraphicsPopContext()

        }

    }

最终结果如下：screenshot

这个实现并不是最干净的，但至少它对我有用。如果我的话中有些不清楚，请随意提问。