Question

private void Form1_Load (object sender, EventArgs e)
{
    Point p1 = new Point (300, 300);
    Point p2 = new Point (120, 120);      

    DrawLine(p1, p2);            
}

private void DrawLine(Point p1, Point p2)
{
    Graphics g = this.CreateGraphics();
    Pen blackPen = new Pen(Color.Black, 1);
    g.DrawLine(blackPen, p1, p2);
}

如果我执行此代码，则不会发生任何事情。

我不想使用Form1_Paint事件，因为我只能通过Start来调用它？

我想在我想要的时候画一条线，我想要的地方和我想要的次数例如我用点数填充2 Textbox es然后点击Button并绘制一条线。

Answer 1

您必须使用FormPaint或类似方法。表单重新绘制有许多原因（这就是为什么FormLoad是错误的地方：如果表单更改其大小，最大化等等，它将被重新绘制并且线条会消失）。相反，Paint在绘制表格时会触发 - 这是进行额外绘画的最佳位置：

  // What to paint: a line [m_FromPoint..m_ToPoint] 
  private Point m_FromPoint = new Point (300, 300);
  private Point m_ToPoint = new Point (120, 120); 

  // Painting itself: whenever form wants painting...
  private void Form1_Paint(object sender, PaintEventArgs e) {
    // ... draw an additional line
    e.Graphics.DrawLine(Pens.Black, m_FromPoint, m_ToPoint);
  }

  // Change painting (on button1 click)
  private void button1_Click(object sender, EventArgs e) {
    // We want a different line...
    m_FromPoint = ... //TODO: put the right point here 
    m_ToPoint = ...   //TODO: put the right point here 

    // ...and we want it at once - force repainting
    Invalidate();
    Update(); 
  }

DrawLine调用函数

1 个答案: