如何为不断调整大小的面板绘制边框 C#

Question

使用面板作为选择指示器。面板根据 MouseMove 事件上的光标位置更改其大小。但是，当我如下绘制边框时，以前的边框会在面板上留下标记，并且在同一面板内显示太多边框。甚至在每次抽奖前都尝试过 refresh() 但这会使它出现故障和缓慢

private void panel1_Paint(object sender, PaintEventArgs e)
{
    this.panel1.Refresh();
    ControlPaint.DrawBorder(e.Graphics, this.panel1.ClientRectangle, Color.DarkBlue, ButtonBorderStyle.Solid);
}

private void drawboard_MouseMove(object sender, MouseEventArgs e)
{
    panel1.Width = e.Location.X - panel1.Left;
    panel1.Height = e.Location.Y - panel1.Top;        
}

Answer 1

首先，您永远不应该在控件绘制处理程序中调用影响控件绘制的方法，例如 Invalidate 或 Refresh。

修改面板大小后调用Invalidate或Refresh即可解决原问题。请注意，最好通过一次调用设置 Size 属性，而不是分别设置 Width 和 Height：

private void panel1_Paint(object sender, PaintEventArgs e)
{
    ControlPaint.DrawBorder(e.Graphics, this.panel1.ClientRectangle, Color.DarkBlue, ButtonBorderStyle.Solid);
}

private void drawboard_MouseMove(object sender, MouseEventArgs e)
{
    var size = new Size(Math.Max(e.Location.X - panel1.Left, 0), 
        Math.Max(e.Location.Y - panel1.Top, 0));
    if (panel1.Size != size)
    {
        panel1.Size = size;
        panel1.Invalidate();
    }
}

更好的选择是将ResizeRedraw property of the selection panel to true. Since it's a protected property, you need to create and use your own Panel subclass. As a bonus, you can also set DoubleBuffered 属性设置为true以避免闪烁，并将绘画代码移到里面：

class SelectionBox : Panel
{
    public SelectionBox()
    {
        ResizeRedraw = true;
        DoubleBuffered = true;
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        ControlPaint.DrawBorder(e.Graphics, ClientRectangle, Color.DarkBlue, ButtonBorderStyle.Solid);
    }
}

将你的 panel1 设为 SelectionBox，移除 Paint 事件处理程序，然后鼠标移动处理程序就可以很简单了

private void drawboard_MouseMove(object sender, MouseEventArgs e)
{
    panel1.Size = new Size(Math.Max(e.Location.X - panel1.Left, 0), 
        Math.Max(e.Location.Y - panel1.Top, 0));
}

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