删除拖放矩形

【问题标题】：Delete drag and drop rectangle删除拖放矩形
【发布时间】：2017-02-10 02:17:49
【问题描述】：

我可以绘制一个拖放矩形，但拖放后，矩形的前一个副本仍在其位置。怎么删除？

namespace dragAndDropRect
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Rectangle rect = new Rectangle(30, 30, 30, 30);
            g.FillRectangle(Brushes.Aqua, rect);

            if (e.Button == MouseButtons.Left)
            {
                Refresh();
                g.FillRectangle(Brushes.AliceBlue, e.X, e.Y, 30, 30);
            }
        }
    }
}

【问题讨论】：

标签： c# drag-and-drop

【解决方案1】：

先处理旧的矩形，然后再新建一个

namespace dragAndDropRect
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        Graphics g = this.CreateGraphics();
        Rectangle rect = new Rectangle(30, 30, 30, 30);
        g.FillRectangle(Brushes.Aqua, rect);

        if (e.Button == MouseButtons.Left)
        {
            Refresh();
            g.Invalidate();
            g.FillRectangle(Brushes.AliceBlue, e.X, e.Y, 30, 30);
        }
    }
}
}

【讨论】：

g.invalidate();无效