如何从另一个 ComboBox 更改形状的颜色（C#，Winforms）

Question

所以我要做的是使用另一个组合框更改形状的颜色。所以第一个组合框表示将显示什么样的形状作为图像。例如，如果我按下三角形选项，它将显示三角形。好吧，我还有另一个组合框，它显示形状将采用哪种颜色。到目前为止，我的代码如下所示：

  using System;
using System.Drawing;
using System.Windows.Forms;

namespace ComboBoxTest
{
   // Form uses a ComboBox to select different shapes to draw
   public partial class ComboBoxTestForm : Form
   {
      // constructor
      public ComboBoxTestForm()
      {
         InitializeComponent();

      } // end constructor
      Pen myPen;
      SolidBrush mySolidBrush;


      private void imageComboBox_SelectedIndexChanged(
         object sender, EventArgs e )
      {


         // create graphics object, Pen and SolidBrush
         Graphics myGraphics = base.CreateGraphics();

         // create Pen using color DarkRed


         // create SolidBrush using color DarkRed


         // clear drawing area setting it to color white
         myGraphics.Clear( Color.White );

         // find index, draw proper shape
         switch ( imageComboBox.SelectedIndex )
         {
            case 0: // case Circle is selected
               myGraphics.DrawEllipse( myPen, 50, 50, 150, 150 );
               break;
            case 1: // case Rectangle is selected
               myGraphics.DrawRectangle( myPen, 50, 50, 150, 150 );
               break;
            case 2: // case Ellipse is selected
               myGraphics.DrawEllipse( myPen, 50, 85, 150, 115 );
               break;
            case 3: // case Pie is selected
               myGraphics.DrawPie(myPen, 50, 50, 150, 150, 0, 45 );
               break;
             case 4:
                Point point1 = new Point(150,  50);
                Point point2 = new Point(100,  150);
                Point point3 = new Point(200,   150);

                Point[] curvePoints =
                         {
                             point1,
                             point2,
                             point3,
                         };

                myGraphics.DrawPolygon(myPen, curvePoints);
               break;
             case 5: // case Filled Circle is selected
               myGraphics.FillEllipse( mySolidBrush, 50, 50, 150, 150 );
               break;
            case 6: // case Filled Rectangle is selected
               myGraphics.FillRectangle( mySolidBrush, 50, 50, 150, 
                  150 );
               break;
            case 7: // case Filled Ellipse is selected
               myGraphics.FillEllipse( mySolidBrush, 50, 85, 150, 115 );
               break;
            case 8: // case Filled Pie is selected
               myGraphics.FillPie( mySolidBrush, 50, 50, 150, 150, 0, 
                  45 );
               break;
             case 9:
                  Point point4 = new Point(150,  50);
                Point point5 = new Point(100,  150);
                Point point6 = new Point(200,   150);

                Point[] curvePoints2 =
                         {
                             point4,
                             point5,
                             point6,
                         };
               myGraphics.FillPolygon(mySolidBrush, curvePoints2);
               break;
         } // end switch

         myGraphics.Dispose(); // release the Graphics object

      }

      private void ComboBoxTestForm_Load(object sender, EventArgs e)
      {

      }

      private void colorComboBox_SelectedIndexChanged(object sender, EventArgs e)
      {

          switch (colorComboBox.SelectedIndex)
          {
              case 0:
                  myPen = new Pen(Color.Black);
                   mySolidBrush = new SolidBrush(Color.Black);
                  break;
          }
      }

      // end method imageComboBox_SelectedIndexChanged
   } // end class ComboBoxTestForm
} 

我试图做的是在 void 之外调用 myPen，因此可以在控制颜色的第二个 void 中调用它。 Mysolidbrush 代表形状的填充。在第二个空白中，我尝试将 myPen 称为 black ，但我没有看到任何变化。我想知道我应该采取哪些步骤才能显示我想要的颜色。

Answer 1

你可以把所有的绘制逻辑放到Paint表单的事件中，然后在SelectedIndexChanged事件中，调用this.Invalidate();：

private void ComboBoxTestForm_Paint(object sender, PaintEventArgs e)
{
    //detect color based on selected index of colorComboBox
    //Create your brush and your pen
    //detect shape based on selected index of imageComboBox
    //draw shares using e.Graphics.DrawXXXX and e.Graphics.FillXXXX


   /*Suppose Color.Redis detected from selected index*/
    var myColor= Color.Red; 
    using ( var myPen = new Pen(myColor))
    {
        /*Suppose drawing ellipse is detected from selected index*/
        e.Graphics.DrawEllipse( myPen, 50, 50, 150, 150 );
    }
}

private void imageComboBox_SelectedIndexChanged(object sender, EventArgs e )
{
    //Makes the form repaint
    this.Invalidate();
}
private void colorComboBox_SelectedIndexChanged(object sender, EventArgs e)
{
    //Makes the form repaint 
    this.Invalidate();        
}

同样在您当前的代码中，虽然您已将 myPen 和 mySolidBrush 定义为类成员，但您从未初始化它们。在colorComboBox_SelectedIndexChanged 中，您分配的是局部变量，而不是类成员。

myPen = new Pen(Color.Black);
mySolidBrush = new SolidBrush(Color.Black);

同样在您当前的代码中，您已将所有绘制逻辑放入 imageComboBox_SelectedIndexChanged，即使您更正了 colorComboBox_SelectedIndexChanged 中的代码并将值分配给您的类成员 myPen 和 mySolidBrush，也就是您的绘图颜色只会改变下一个形状。