c# - 拖放图像

Question

使用此代码，我可以将图像拖放到标签上，但现在我想将该图像从标签拖到另一个标签上。我怎样才能做到这一点？

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
            Image img = Image.FromFile(@"D:\test\test.png");
            this.btnImage.Image = img;

            Image img1 = Image.FromFile(@"C:\Documents and Settings\SAURABH\Desktop\Green.ico");
            this.btnImage1.Image = img1;
        }

        private void button1_MouseDown(object sender, MouseEventArgs e)
        {
            Button btnPic = (Button)sender;
            btnPic.DoDragDrop(btnPic.Image, DragDropEffects.Copy);
        }

        private void button2_MouseDown(object sender, MouseEventArgs e)
        {
            Button btnPic = (Button)sender;
            btnPic.DoDragDrop(btnPic.Image, DragDropEffects.Copy);
        }

        private void button3_MouseDown(object sender, MouseEventArgs e)
        {
            Button btnPic = (Button)sender;
            btnPic.DoDragDrop(btnPic.Image, DragDropEffects.Copy);
        }

        private void label1_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Bitmap))
            {
                e.Effect = DragDropEffects.Copy;
            }
            else
            {
                e.Effect = DragDropEffects.None;
            }
        }

        private void label10_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Bitmap))
            {
                e.Effect = DragDropEffects.Copy;
            }
            else
            {
                e.Effect = DragDropEffects.None;
            }
        }

        private void label10_DragDrop(object sender, DragEventArgs e)
        {
            Label picbox = (Label)sender;
            //PictureBox picbox = (PictureBox)sender;
            Graphics g = picbox.CreateGraphics();
            g.DrawImage((Image)e.Data.GetData(DataFormats.Bitmap), new Point(0, 0));
        }

        private void label1_DragDrop(object sender, DragEventArgs e)
        {
            Label picbox = (Label)sender;
            //PictureBox picbox = (PictureBox)sender;
            Graphics g = picbox.CreateGraphics();
            g.DrawImage((Image)e.Data.GetData(DataFormats.Bitmap), new Point(0, 0));
        }
    }
}

Answer 1

问题出在您Label的 DragDrop 处理程序中。您可以使用如下代码直接复制拖放操作的“有效负载”：

private void Label_DragDrop(object sender, DragEventArgs e) {
    if (e.Data.GetDataPresent(typeof(Bitmap))) {
        ((Label)sender).Image = (Image)e.Data.GetData(DataFormats.Bitmap);
    }
}

您可能会发现这篇关于拖放的 MSDN 文章很有用。

我还在您的代码中注意到MouseDown,DragEnter和DragDrop事件处理程序对于多个Button和Label控件是相同的。您可以通过编写每个处理程序一次然后将多个控件的事件注册到每个处理程序来重构一些东西。例如，您可以将您的Label1和Label10的 DragDrop 事件注册到我上面提供的处理程序中。在 Designer 中或通过代码执行此操作：

label1.DragDrop += Label_DragDrop;
label10.DragDrop += Label_DragDrop;