form1.PointToClient( panel1.PointToScreen(button1.Location) );
這個步驟分爲2步
第一步，將buttion1在panel1中的座標轉換爲屏幕座標
第二部，將屏幕座標轉換爲在form1中的座標。
下面的代碼實例使用用戶能夠將圖像或圖像文件拖到窗體上，並使它再放置點顯示。每次繪製窗體時，都重寫OnPaint方法以重新繪製圖像；
否則圖像將保持到下一次重新繪製。DragEnter事件處理方法決定拖到窗體中的數據的類型，並提供適當的反饋，如果Image可以從數據中創建，
則DragDrop事件處理方法就會在該窗體上先生此圖像。因此DragEventArgs.X和DragEventArgs.Y值爲屏幕座標，所以使用PrintToClient方法將
它們轉換成工作區座標。
public Form1()
{
// InitializeComponent();
this.AllowDrop = true;
this.DragDrop += new DragEventHandler(this.Form1_DragDrop);
this.DragEnter += new DragEventHandler(this.Form1_DragEnter);
}
protected override void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
base.OnPaint(e);
if (this.picture != null && this.pictureLocation != Point.Empty)
{
e.Graphics.DrawImage(this.picture, this.pictureLocation);
}
}
private void Form1_DragDrop(object sender, DragEventArgs e)
{
// Handle FileDrop data.
if (e.Data.GetDataPresent(DataFormats.FileDrop))
{
// Assign the file names to a string array, in
// case the user has selected multiple files.
string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
try
{
// Assign the first image to the picture variable.
this.picture = Image.FromFile(files[0]);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y));
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Handle Bitmap data.
if (e.Data.GetDataPresent(DataFormats.Bitmap))
{
try
{
// Create an Image and assign it to the picture variable.
this.picture = (Image)e.Data.GetData(DataFormats.Bitmap);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y));
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Force the form to be redrawn with the image.
this.Invalidate();
}
private void Form1_DragEnter(object sender, DragEventArgs e)
{
// If the data is a file or a bitmap, display the copy cursor.
if (e.Data.GetDataPresent(DataFormats.Bitmap) ||
e.Data.GetDataPresent(DataFormats.FileDrop))
{
e.Effect = DragDropEffects.Copy;
}
else
{
e.Effect = DragDropEffects.None;
}
}