从 X 值获取跨 .NET 图表系列的 Y 值

Question

将 C# 与 .NET 图表结合使用。

我正在尝试绘制几个波形，我希望将鼠标移过图表区域，并让我的工具提示在此 X 值位置显示图表中每个系列的 Y 值。

|      at xValue 12    |                                     |
|      _ = 3           |                                     |
|      * = 2           |                                * *  |
|              ________|______________________________*_____ |
|             /        |                             *       |
| __________*/*********|*****************************        |
|        *             |                                     |
|       *              |                                     |
|______________________|_____________________________________|

有点像上面这张图。以下是我的代码的一个版本：

void chart1_MouseMove(object sender, MouseEventArgs e)
        {
            var pos = e.Location;
            _point.X = e.Location.X;
            _point.Y = e.Location.Y;

            try
            {
                if ((chart1.ChartAreas[0].AxisX.PixelPositionToValue(e.X) >= 0) && (chart1.ChartAreas[0].AxisX.PixelPositionToValue(e.X) <= max))
                {
                    //Crossair
                    chart1.ChartAreas[0].CursorX.SetCursorPixelPosition(_point, true);

                    //Tooltips
                    double xValue = chart1.ChartAreas[0].AxisX.PixelPositionToValue(e.X);
                    double yValue = chart1.ChartAreas[0].AxisY.PixelPositionToValue(e.Y);
                    string all_Data_Values = "";

                    foreach (var series in chart1.Series)
                    {
                        all_Data_Values = all_Data_Values + Environment.NewLine + series.Name + ": " + yValue;
                    }

                    tooltip.Show("At " + Math.Truncate(xValue * 1000) / 1000 + all_Data_Values, this.chart1, pos.X - 40, pos.Y - 20);
                }
            }
            catch (Exception exception)
            {
               //
            }
        }

这就是我所拥有的，现在它只显示我的鼠标光标位置的 Y 值。我尝试了其他代码，试图以某种方式将 x 值映射到 chart1.Series[] 但它也不起作用。

Answer 1

（这是对代码请求的响应，以在给定像素坐标的情况下查找最接近的值。）

我的做法与您有所不同，因为我实际上是在用户移动鼠标时设置图表的“光标”，但希望这将为您提供足够的信息以使其适应您的需求。 ..

这是我计算客户端 X 坐标的 X 轴坐标的方法：

private double calcCursorGraphX(int clientX)
{
    var xAxis = _chart.ChartAreas[CHART_INDEX].AxisX;
    int xRight = (int) xAxis.ValueToPixelPosition(xAxis.Maximum) - 1;
    int xLeft = (int) xAxis.ValueToPixelPosition(xAxis.Minimum);

    if (clientX > xRight)
    {
        return xAxis.Maximum;
    }
    else if (clientX < xLeft)
    {
        return xAxis.Minimum;
    }
    else
    {
        return xAxis.PixelPositionToValue(clientX);
    }
}

给定从上述方法返回的 X 值，我们可以查找最近的前一个值：

private int nearestPreceedingValue(double x)
{
    var bpData  = _chart.Series[SERIES_INDEX].Points;
    int bpIndex = bpData.BinarySearch(x, (xVal, point) => Math.Sign(x - point.XValue));

    if (bpIndex < 0)
    {
        bpIndex = ~bpIndex;                // BinarySearch() returns the index of the next element LARGER than the target.
        bpIndex = Math.Max(0, bpIndex-1);  // We want the value of the previous element, so we must decrement the returned index.
    }                                      // If this is before the start of the graph, use the first valid data point.

    return bpIndex;
}

然后你有一个索引，你可以使用它来查找来自_chart.Series[SERIES_INDEX].Points的值

我不确定这是否符合您的数据在图表中的存储方式，但我就是这样做的。

[编辑] 这是缺少的 BinarySearch 扩展方法。将其添加到可访问的静态类中。如果您不使用代码合同，请用您自己的错误处理替换“合同”内容。

/// <summary>
/// Searches the entire sorted IList{T} for an element using the specified comparer 
/// and returns the zero-based index of the element.
/// </summary>
/// <typeparam name="TItem">The type of the item.</typeparam>
/// <typeparam name="TSearch">The type of the searched item.</typeparam>
/// <param name="list">The list to be searched.</param>
/// <param name="value">The value to search for.</param>
/// <param name="comparer">The comparer that is used to compare the value with the list items.</param>
/// <returns>
/// The zero-based index of item in the sorted IList{T}, if item is found; 
/// otherwise, a negative number that is the bitwise complement of the index of the next element that is larger than item,
/// or - if there is no larger element - the bitwise complement of Count.
/// </returns>

public static int BinarySearch<TItem, TSearch>(this IList<TItem> list, TSearch value, Func<TSearch, TItem, int> comparer)
{
    Contract.Requires(list != null);
    Contract.Requires(comparer != null);

    int lower = 0;
    int upper = list.Count - 1;

    while (lower <= upper)
    {
        int middle = lower + (upper - lower) / 2;
        int comparisonResult = comparer(value, list[middle]);

        if (comparisonResult < 0)
        {
            upper = middle - 1;
        }
        else if (comparisonResult > 0)
        {
            lower = middle + 1;
        }
        else
        {
            return middle;
        }
    }

    return ~lower;
}