自定义和事件
在图表控件中，可以使用事件来自定义图表行为，例如执行自定义绘制。 ASP.NET 和 Windows 窗体的图表控件公开不同的事件组。 有关每个控件的完整事件列表，请参见 Chart 和 Chart。
PrePaint 和 PostPaint
PrePaint 和 PostPaint 事件是最常用的事件。 在绘制每个图表元素之前和之后将分别触发这两个事件。
备注
若为图表区域启用三维，则不会为 Series 对象触发这两个事件。
若要确定为哪个图表元素触发了当前事件，请使用 ChartPaintEventArgs.ChartElement 属性。
下面的事件处理程序将在绘制 Series 元素并强调名为“Product F”的数据点后，绘制六个同心圆。
Private Sub chart1_PostPaint(ByVal sender As Object, ByVal e As ChartPaintEventArgs)
If TypeOf e.ChartElement Is Series Then
Dim series As Series = DirectCast(e.ChartElement, Series)
Dim position As System.Drawing.PointF = System.Drawing.PointF.Empty
' Find data point with label "Product F".
For Each point As DataPoint In series.Points
position.X += 1
If point.AxisLabel = "Product F" Then
position.Y = CSng(point.YValues(0))
Exit For
End If
Next
' Get relative coordinates of the data point values found.
position.X = CSng(e.ChartGraphics.GetPositionFromAxis("Default", AxisName.X, position.X))
position.Y = CSng(e.ChartGraphics.GetPositionFromAxis("Default", AxisName.Y, position.Y))
' Convert relative coordinates to absolute coordinates.
position = e.ChartGraphics.GetAbsolutePoint(position)
' Draw custom object.
For radius As Integer = 20 To 79 Step 10
e.ChartGraphics.Graphics.DrawEllipse(System.Drawing.Pens.Red, position.X - radius / 2, _
position.Y - radius / 2, radius, radius)
Next
End If
End Sub
private void chart1_PostPaint(object sender, ChartPaintEventArgs e)
{
if (e.ChartElement is Series)
{
Series series = (Series)e.ChartElement;
System.Drawing.PointF position = System.Drawing.PointF.Empty;
// Find data point with label "Product F".
foreach (DataPoint point in series.Points)
{
++position.X;
if (point.AxisLabel == "Product F")
{
position.Y = (float)point.YValues[0];
break;
}
}
// Get relative coordinates of the data point values found.
position.X = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.X, position.X);
position.Y = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.Y, position.Y);
// Convert relative coordinates to absolute coordinates.
position = e.ChartGraphics.GetAbsolutePoint(position);
// Draw custom object.
for (int radius = 20; radius < 80; radius += 10)
{
e.ChartGraphics.Graphics.DrawEllipse(System.Drawing.Pens.Red, position.X - radius / 2,
position.Y - radius / 2, radius, radius);
}
}
}