自訂和事件
在圖表控制項中，您可以使用事件自訂圖表行為，例如執行自訂繪圖。適用於 ASP.NET 和 Windows Form 的圖表控制項會公開不同的一組事件。如需各控制項的完整事件清單，請參閱 System.Web.UI.DataVisualization.Charting.Chart 和 System.Windows.Forms.DataVisualization.Charting.Chart。
PrePaint 和 PostPaint
PrePaint 和 PostPaint 事件是最常使用的事件。這些事件會在繪製每個圖表項目之前和之後觸發。
[!附註]
當圖表區域啟用 3D 時，則不會觸發 Series 物件的這兩個事件。
若要找出觸發目前事件的圖表項目，請使用 ChartPaintEventArgs.ChartElement 屬性。
下列事件處理常式會在繪製 Series 項目後繪製六個同心圓，並強調名為 "Product F" 的資料點。
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);
}
}
}