在PictureBox中使用PictureBox.CreateGraphics創建矩形

Question

下面代碼中的按鈕點擊函數我想在picureBox中創建一個矩形，但是當我第一次執行它時什麼都不畫，但是第二次單擊矩形會出現，爲什麼？

if語句在兩個時間都是true。

private void btnChamber_Click(object sender, EventArgs e) 
    { 

     //pictureBox1.Visible = true; 

     if (cmbShowResult.SelectedIndex == 0 && ChamberType.SelectedIndex == 0) 
     { 
      chart1.Visible = false; 
      chart2.Visible = false; 
      chart3.Visible = false; 
      chart4.Visible = false; 
      chart5.Visible = false; 
      pictureBox1.Visible = true; 
      //pictureBox1.Enabled = true; 
      Graphics gg = pictureBox1.CreateGraphics(); 

      //gg.ClipBounds.X = 0; 
      //gg.ClipBounds.Y = 0; 
      //AddChartStyle(gg); 
      chartArea1.X = 0; 
      chartArea1.Y = 0; 
      chartArea1.Height = 298; 
      chartArea1.Width = 450; 


      plotArea.X = 40; 
      plotArea.Y = 10; 
      plotArea.Height = 258; 
      plotArea.Width = 400; 



      xLimMin = -(float.Parse(txtWidth.Text))/2; 
      xLimMax = (float.Parse(txtWidth.Text))/2; 
      yLimMin = -(float.Parse(txtLeft.Text)) * 3f; 
      yLimMax = (float.Parse(txtLeft.Text)) * 3f; 

      Pen aPen = new Pen(chartBorderColor, 1f); 
      SolidBrush aBrush = new SolidBrush(chartBorderColor); 
      gg.FillRectangle(aBrush, chartArea1); 
      gg.DrawRectangle(aPen, chartArea1); 
      aPen = new Pen(plotBorderColor, 1f); 
      aBrush = new SolidBrush(plotBackColor); 
      gg.FillRectangle(aBrush, plotArea); 

      gg.DrawRectangle(aPen, plotArea); 
      //AddChartStyle(g); 

      //pictureBox1.Visible = true; 
      //gg = pictureBox1.CreateGraphics(); 


      //gg.Flush(); 
      //gg.Save(); 
      //pictureBox1.Show(); 
      //pictureBox1.Invalidate(); 
      //chart6.Visible = true; 

     } 
     pictureBox1.Visible = true; 
     //gg.Flush(); 

    } 

Answer 1

因爲您正在Click事件中執行此操作。你應該在Paint事件中完成它。