c# - 得到两个椭圆而不是一个

Question

所以我有一段代码需要在随机位置绘制一个圆，并且它还需要保持在预定义的边界内。在我的代码中，我应该只画一个圆圈。在某些情况下，它只绘制一个，但在其他情况下，它绘制两个，我不知道为什么。

private void Form1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    Random r = new Random();

    int leftX = 20;
    int topY = 60;
    int width = this.Width - (3 * leftX);
    int height = this.Height - (int)(2.5 * topY);

    float x = r.Next(20, width - 100);
    float y = r.Next(60, height - 100);

    Rectangle rect = new Rectangle((int)x, (int)y, 100, 100);
    g.DrawRectangle(new Pen(Color.Black), rect); //rectangle around ellipse
    g.DrawRectangle(new Pen(Color.Black, 3), leftX, topY, width, height); //border rectangle

    g.FillEllipse(new SolidBrush(Color.Black), rect);
}

Answer 1

每当 form is re-drawn 时，绘制事件就会被调用，所以从你的角度来看，这是不可预测的。您最好将代码移动到加载事件中以生成位置:

float x;
float y;
private void Form1_Load(object sender, System.EventArgs e)
{
    Random r = new Random();
    x = r.Next(20, width - 100);
    y = r.Next(60, height - 100);

}

private void Form1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;

    int leftX = 20;
    int topY = 60;
    int width = this.Width - (3 * leftX);
    int height = this.Height - (int)(2.5 * topY);

    Rectangle rect = new Rectangle((int)x, (int)y, 100, 100);
    g.DrawRectangle(new Pen(Color.Black), rect); //rectangle around ellipse
    g.DrawRectangle(new Pen(Color.Black, 3), leftX, topY, width, height); //border rectangle

    g.FillEllipse(new SolidBrush(Color.Black), rect);
}