如何使用鼠標在C＃中繪製矩形

Question

我想在C＃中的窗體上繪製矩形。我閱讀並發現這個article。是否有任何樣本或教程可用？文章不是很有幫助。

Answer 1

您鏈接的文章似乎是C++，這可能解釋爲什麼它沒有多大幫助。

如果您爲MouseDown和MouseUp創建事件，則應該有一個矩形所需的兩個角點。從那裏，這是一個繪製在形式上的問題。 System.Drawing。*應該可能是您的第一站。有一對夫婦教程鏈接如下：

Drawing with Graphics in WinForms using C#

Draw a rectangle using Winforms (StackOverflow)

Graphics Programming using C#

Answer 2

你需要這個3函數和變量：

private Graphics g; 
    Pen pen = new System.Drawing.Pen(Color.Blue, 2F); 
    private Rectangle rectangle; 
    private int posX, posY, width, height; 

其次，你需要做一個鼠標關機事件：

private void pictureCrop_MouseDown(object sender, MouseEventArgs e) 
    { 
     if (e.Button == MouseButtons.Left) 
     { 
      posX = e.X; 
      posY = e.Y; 
     } 
    } 

第三，你需要implemente鼠標向上事件：

private void pictureCrop_MouseUp(object sender, MouseEventArgs e) 
    { 
     if (e.Button != MouseButtons.Left) 
      return; 

     if (e.X > posX && e.Y > posY) // top left to bottom right 
     { 
      width = Math.Abs(e.X - posX); 
      height = Math.Abs(e.Y - posY); 
     } 
     else if (e.X < posX && e.Y < posY) // bottom right to top left 
     { 
      width = Math.Abs(posX - e.X); 
      height = Math.Abs(posY - e.Y); 

      posX = e.X; 
      posY = e.Y; 
     } 
     else if (e.X < posX && e.Y > posY) // top right to bottom left 
     { 
      width = Math.Abs(posX - e.X); 
      height = Math.Abs(posY - e.Y); 

      posX = e.X; 
     } 
     else if (e.X > posX && e.Y < posY) // bottom left to top right 
     { 
      width = Math.Abs(posX - e.X); 
      height = Math.Abs(posY - e.Y); 

      posY = e.Y; 
     } 

     g.DrawImage(_bitmap, 0, 0); 
     rectangle = new Rectangle(posX, posY, width, height); 
     g = pictureCrop.CreateGraphics(); 
     g.DrawRectangle(pen, rectangle); 
    } 

並保證當你調整大小或移動窗體矩形將在那裏：

protected override void OnPaint(PaintEventArgs e) 
    { 
     base.OnPaint(e); 

     Graphics graph = e.Graphics; 
     graph.DrawImage(_bitmap, 0, 0); 
     Rectangle rec = new Rectangle(posX, posY, width, height); 
     graph.DrawRectangle(pen, rec); 
    }