(这是为了响应代码请求,以查找给定像素坐标的最接近值。)
我的做法与您略有不同,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,以便您使其适应您的需求......
以下是我计算客户端 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;
}
然后你就有了一个索引,你可以用它来查找值_chart.Series[SERIES_INDEX].Points
我不确定这是否适合您的数据在图表中存储的方式,但这就是我的做法。
[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。如果您不使用代码契约,请将“契约”内容替换为您自己的错误处理。
/// <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;
}