从类实例获取带有Graphics的控件对象(getting control object with Graphics from class instance)

从类实例获取带有Graphics的控件对象(getting control object with Graphics from class instance)

我对winforms中的Graphics类没有多少经验。 我只是在它的草绘阶段（也是我添加的代码）。 我的问题是我正在尝试创建一个面板： clockPanel有一些图形，没有异常被抛出但面板（我在UI中可以看到）上没有图形。 试图寻找例子但我无法在我的代码中找到错误或遗漏的东西。 对于那些有图形经验的人来说，它可能很容易。 谢谢你的时间考虑。

VB代码： 通过实例将'clockpanel'面板添加到其他pannel（'secondaryPannel'）到GoalsClock类

Public Class ManagersTab ... Public Sub BuiledDashBoard() ... Dim p As GoalsClock = New GoalsClock(100, 100, 0.8) p.Create() p.clockPanel.Location = New Point(200, 100) secondaryPannel.Controls.Add(p.clockPanel) ... End Sub ... End Class

Create（）方法是最相关的部分：

Class GoalsClock Private Gclock As Graphics Private clockWidth As Int16 Private clockHeight As Int16 Private xPos As Int16 Private yPos As Int16 Public clockPanel As Panel Private panelColor As Color Private PercentTextColor As Color ' rectangles to store squares Protected OuterRect As Rectangle Protected InnerRect As Rectangle Protected InnerStringBrush As Brush Protected InnerStringColor As Color Protected InnerStringFontSize As Byte ' inner square Private InnerSquarePen As Pen Private InnerSquarePen_Color As Color Private InnerSquarePen_Width As Byte ' outer square Private OuterSquarePen As Pen Private OuterSquarePen_Color As Color Private OuterSquarePen_Width As Byte Private _PercentOfGoals As Single ' to calculate the goals deg arc Public Property PercentOfGoals() As Single Get Return _PercentOfGoals * 100 End Get Private Set(ByVal value As Single) If value <= 1.0F Then _PercentOfGoals = value Else value = 0 End If End Set End Property Sub New(ByVal clockWidth As Int16, ByVal clockHeight As Int16, ByVal GoalsPercent As Single) Me.clockWidth = clockWidth Me.clockHeight = clockHeight PercentOfGoals = GoalsPercent ' values for test xPos = 0 yPos = 0 InnerStringFontSize = 12 OuterSquarePen = New Pen(Color.Gray) InnerSquarePen = New Pen(Color.Cyan) OuterSquarePen_Width = 23 InnerSquarePen_Width = 15 End Sub ''' <summary> ''' ''' create graphics of the goals clock on clockPanel ''' </summary> ''' <remarks></remarks> Public Sub Create() ' panel clockPanel = New Panel() clockPanel.Size = New Size(clockWidth, clockHeight) clockPanel.BackColor = Color.Beige Gclock = clockPanel.CreateGraphics() ' create outer rectangle OuterRect = New Rectangle(xPos, yPos, clockWidth, clockHeight) ' create inner rectangle Dim w, h, x, y As Integer getInnerRectSizeAndLocation(w, h, x, y) InnerRect = New Rectangle(x, y, w, h) ' draw goals string inside inner rect InnerStringBrush = Brushes.Cyan Gclock.DrawString(getPercentString(), New Font("ARIAL", InnerStringFontSize, FontStyle.Bold), InnerStringBrush, InnerRect) ' create outer square OuterSquarePen = New Pen(OuterSquarePen_Color, OuterSquarePen_Width) Gclock.DrawArc(OuterSquarePen, OuterRect, 1.0F, 360.0F) ' create inner square InnerSquarePen = New Pen(InnerSquarePen_Color, InnerSquarePen_Width) Dim sweepAngle As Short = getSweepAngleFromGoalsPercent() Gclock.DrawArc(InnerSquarePen, OuterRect, -90.0F, sweepAngle) End Sub Private Sub getInnerRectSizeAndLocation(ByRef w As Integer, ByRef h As Integer, ByRef x As Integer, ByRef y As Integer) ' values for test w = 40 h = 40 x = 64 y = 65 End Sub Private Function getPercentString() As String Return PercentOfGoals.ToString() & "%" End Function Private Function getSweepAngleFromGoalsPercent() As Single ' value for test Return 0.0F End Function End Class

i dont have much experience with Graphics class in winforms. i am only in the sketching stage of it (also the code i have added). my problem is that i am trying to create a panel: clockPanel with some graphics on it, no exception is thrown but the panel (as i can see in the UI) have no graphics on it. tryed to look for examples but i cant find mistakes or something i missed in my code. probably its an easy one for those of you that experienced with graphics. thank you for your time an consideration.

VB CODE: adding 'clockpanel' panel to other pannel ('secondaryPannel') via instance to GoalsClock class

Public Class ManagersTab ... Public Sub BuiledDashBoard() ... Dim p As GoalsClock = New GoalsClock(100, 100, 0.8) p.Create() p.clockPanel.Location = New Point(200, 100) secondaryPannel.Controls.Add(p.clockPanel) ... End Sub ... End Class

Create() method is the most relevant part:

Class GoalsClock Private Gclock As Graphics Private clockWidth As Int16 Private clockHeight As Int16 Private xPos As Int16 Private yPos As Int16 Public clockPanel As Panel Private panelColor As Color Private PercentTextColor As Color ' rectangles to store squares Protected OuterRect As Rectangle Protected InnerRect As Rectangle Protected InnerStringBrush As Brush Protected InnerStringColor As Color Protected InnerStringFontSize As Byte ' inner square Private InnerSquarePen As Pen Private InnerSquarePen_Color As Color Private InnerSquarePen_Width As Byte ' outer square Private OuterSquarePen As Pen Private OuterSquarePen_Color As Color Private OuterSquarePen_Width As Byte Private _PercentOfGoals As Single ' to calculate the goals deg arc Public Property PercentOfGoals() As Single Get Return _PercentOfGoals * 100 End Get Private Set(ByVal value As Single) If value <= 1.0F Then _PercentOfGoals = value Else value = 0 End If End Set End Property Sub New(ByVal clockWidth As Int16, ByVal clockHeight As Int16, ByVal GoalsPercent As Single) Me.clockWidth = clockWidth Me.clockHeight = clockHeight PercentOfGoals = GoalsPercent ' values for test xPos = 0 yPos = 0 InnerStringFontSize = 12 OuterSquarePen = New Pen(Color.Gray) InnerSquarePen = New Pen(Color.Cyan) OuterSquarePen_Width = 23 InnerSquarePen_Width = 15 End Sub ''' <summary> ''' ''' create graphics of the goals clock on clockPanel ''' </summary> ''' <remarks></remarks> Public Sub Create() ' panel clockPanel = New Panel() clockPanel.Size = New Size(clockWidth, clockHeight) clockPanel.BackColor = Color.Beige Gclock = clockPanel.CreateGraphics() ' create outer rectangle OuterRect = New Rectangle(xPos, yPos, clockWidth, clockHeight) ' create inner rectangle Dim w, h, x, y As Integer getInnerRectSizeAndLocation(w, h, x, y) InnerRect = New Rectangle(x, y, w, h) ' draw goals string inside inner rect InnerStringBrush = Brushes.Cyan Gclock.DrawString(getPercentString(), New Font("ARIAL", InnerStringFontSize, FontStyle.Bold), InnerStringBrush, InnerRect) ' create outer square OuterSquarePen = New Pen(OuterSquarePen_Color, OuterSquarePen_Width) Gclock.DrawArc(OuterSquarePen, OuterRect, 1.0F, 360.0F) ' create inner square InnerSquarePen = New Pen(InnerSquarePen_Color, InnerSquarePen_Width) Dim sweepAngle As Short = getSweepAngleFromGoalsPercent() Gclock.DrawArc(InnerSquarePen, OuterRect, -90.0F, sweepAngle) End Sub Private Sub getInnerRectSizeAndLocation(ByRef w As Integer, ByRef h As Integer, ByRef x As Integer, ByRef y As Integer) ' values for test w = 40 h = 40 x = 64 y = 65 End Sub Private Function getPercentString() As String Return PercentOfGoals.ToString() & "%" End Function Private Function getSweepAngleFromGoalsPercent() As Single ' value for test Return 0.0F End Function End Class

最满意答案

您必须订阅面板的Paint事件并在那里执行所有绘图。 AddHandler语句用于动态订阅事件。

Graphics类不会存储有关您绘制内容的任何信息，因此当您的面板重新绘制时，您之前绘制的所有内容都将消失，除非您再次绘制它。 这是Paint事件发挥作用的地方：每次重绘面板时都会引发它，在其PaintEventArgs传递Graphics类的实例，这样你就可以再次将你的东西绘制到面板上。

Public Sub Create() ' panel clockPanel = New Panel() clockPanel.Size = New Size(clockWidth, clockHeight) clockPanel.BackColor = Color.Beige ' subscribe to the panel's paint event AddHandler clockPanel.Paint, AddressOf clockPanel_Paint End Sub Private Sub clockPanel_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Dim Gclock As Graphics = e.Graphics 'Local variable only, as the Graphics object might change. ' create outer rectangle OuterRect = New Rectangle(xPos, yPos, clockWidth, clockHeight) ' create inner rectangle Dim w, h, x, y As Integer getInnerRectSizeAndLocation(w, h, x, y) InnerRect = New Rectangle(x, y, w, h) ' draw goals string inside inner rect InnerStringBrush = Brushes.Cyan Gclock.DrawString(getPercentString(), New Font("ARIAL", InnerStringFontSize, FontStyle.Bold), InnerStringBrush, InnerRect) ' create outer square OuterSquarePen = New Pen(OuterSquarePen_Color, OuterSquarePen_Width) Gclock.DrawArc(OuterSquarePen, OuterRect, 1.0F, 360.0F) ' create inner square InnerSquarePen = New Pen(InnerSquarePen_Color, InnerSquarePen_Width) Dim sweepAngle As Short = getSweepAngleFromGoalsPercent() Gclock.DrawArc(InnerSquarePen, OuterRect, -90.0F, sweepAngle) End Sub

正如您可能已经看到我在Paint事件中不断重新声明一个新的Gclock变量。 这是因为用于绘制面板的Graphics实例可能会更改，因此您不应该存储它超过Paint事件持续时间（因此我强烈建议您删除类顶部的声明）。

You must subscribe to the panel's Paint event and perform all drawing there. The AddHandler statement is used to dynamically subscribe to events.

The Graphics class will not store any information about what you draw, so when your panel is redrawn everything you previously drew will be gone unless you draw it again. This is where the Paint event comes into play: it will be raised every time your panel is redrawn, passing an instance of a Graphics class in its PaintEventArgs so you can draw your stuff onto the panel again.

Public Sub Create() ' panel clockPanel = New Panel() clockPanel.Size = New Size(clockWidth, clockHeight) clockPanel.BackColor = Color.Beige ' subscribe to the panel's paint event AddHandler clockPanel.Paint, AddressOf clockPanel_Paint End Sub Private Sub clockPanel_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Dim Gclock As Graphics = e.Graphics 'Local variable only, as the Graphics object might change. ' create outer rectangle OuterRect = New Rectangle(xPos, yPos, clockWidth, clockHeight) ' create inner rectangle Dim w, h, x, y As Integer getInnerRectSizeAndLocation(w, h, x, y) InnerRect = New Rectangle(x, y, w, h) ' draw goals string inside inner rect InnerStringBrush = Brushes.Cyan Gclock.DrawString(getPercentString(), New Font("ARIAL", InnerStringFontSize, FontStyle.Bold), InnerStringBrush, InnerRect) ' create outer square OuterSquarePen = New Pen(OuterSquarePen_Color, OuterSquarePen_Width) Gclock.DrawArc(OuterSquarePen, OuterRect, 1.0F, 360.0F) ' create inner square InnerSquarePen = New Pen(InnerSquarePen_Color, InnerSquarePen_Width) Dim sweepAngle As Short = getSweepAngleFromGoalsPercent() Gclock.DrawArc(InnerSquarePen, OuterRect, -90.0F, sweepAngle) End Sub

As you also might've seen I am constantly redeclaring a new Gclock variable in the Paint event. This is because the Graphics instance used to draw your panel with might change, so you shouldn't store it any longer than the time the Paint event lasts (so I highly recommend you remove the declaration in the top of your class).