使用图例

本示例内容可以参考CaseStudy目录下的文件"地图.Table"的示例十五。

本节的任务是在上一节的基础上加上图例：

提示：本节的代码使用了lambda过程，如果你还不熟悉，请参考：使用lambda过程

示例

1、将Map控件的"地图来源"属性设置为"None"

2、将窗口的AfterLoad事件代码设置为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
Dim layer As New VectorLayer()
map.Layers.Add(layer)
layer.Style.Stroke.Color = Color.Gray
Dim minValue As Double = DataTables("市").Compute("Min(人均GDP)")
Dim maxValue As Double = DataTables("市").Compute("Max(人均GDP)")
Dim minColor As Color = Color.FromArgb(230, 247, 255) ' 浅蓝
Dim maxColor As Color = Color.FromArgb(74, 0, 114) '深紫
'定义一个lambda过程，用于根据GDP计算背景颜色
Dim getValueColor =
Function(tValue As Double)
    Dim radio As Double
    tValue = Math.Min(tValue, maxValue)
    radio = tValue / maxValue
    Dim red As Byte = minColor.R + (CInt(maxColor.R) - CInt(minColor.R)) * radio
    Dim green As Byte = minColor.G + CInt((maxColor.G) - CInt(minColor.G)) * radio
    Dim blue As Byte = minColor.B + (CInt(maxColor.B) - CInt(minColor.B)) * radio
    Return Color.FromArgb(red, green, blue)
End Function
'绘制市级行政区
For Each dr As DataRow In DataTables("行政区域").Select("level = 2 or (level = 3 and parentLevel = 1)")
    Dim polygon As VectorPolygon = map.CreatePolygon(dr("geometry"), 5)
    layer.Items.Add(Polygon)
    Dim sr As DataRow = DataTables("市").Find("市代码 = '" & dr("adcode") & "'")
    If sr IsNot Nothing Then
        Dim gdp As Double = sr("人均GDP")
        polygon.Style.BackColor = getValueColor.Invoke(gdp)
        polygon.Tag = dr("name") & ":" & sr("人均GDP")
    Else
        polygon.Tag = dr("name")
    End If
Next
'增加图例
Dim legend As New MapLegend '定义图例
map.Legends.Add(legend) '增加图例
legend.Alignment = ContentAlignment.MiddleRight '图例位置为中间靠右
legend.Layout = MapLegendLayout.Column '垂直显示
legend.Style.BackColor = Color.White '设置背景颜色为白色，避免和地图重叠的时候难以识别
legend.Margin = New Padding(10) '边距设置为10，避免图例紧贴在窗口边框
For value As Integer = 0 To maxvalue Step 5 '从0开始，以5(万)为间隔增加一个图例项目
    Dim item As New MapLegendItem
    item.Size = New Size(20, 20)
    item.Kind = C1.FlexMap.MapLegendItemKind.Rectangle
    item.Style.BackColor = getValueColor.Invoke(value) '如果不想使用渐变，可以不设置BackColor2
    item.Style.BackColor2 = getValueColor.Invoke(value + 5)
    item.Style.Stroke.Color = Color.LightGray
    item.Style.Alignment = ContentAlignment.MiddleLeft
    item.Label = value.ToString()
    legend.Items.Add(item)
Next