用于在运行时移动图片框的DragDrop

Question

我有一个名为pic的PictureBox，放在另一个名为picTrack的PictureBox中。

我的目标是能够让用户在运行时通过拖动来改变pic的位置。

这就是我到目前为止所知道的：

    int x_offset = 0; // any better to do this without having a global variable?
    int y_offset = 0;
    void pic_MouseDown(object sender, MouseEventArgs e)
    {
        PictureBox me = (PictureBox)sender;
        x_offset = me.Left - e.X;
        y_offset = me.Top - e.Y;
    }

    void pic_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            PictureBox me = (PictureBox)sender;
            me.Left = e.X + x_offset; 
            me.Top = e.Y + y_offset;
            picTrack.Invalidate();
        }
    }

这段代码只能在非常基础的级别上工作。我有两个问题：

1.)如果用户不松开鼠标按钮，则不更新picTrack。当pic被移动时，可以看到pic的幽灵图像(就像pic有一条尾巴)。

2.) pic正在“咯咯地笑”(即在其位置周围快速左右摇晃、上下摇晃)。

我应该如何解决这两个问题，并创建一个更流畅的拖放？谢谢。

Answer 1

在这里，这实际上是有效的，我以前写了相当多的拖拽的东西..它可能并不完美，但这应该会给你提供一些有用的东西。

    Point dragPoint = Point.Empty;
    bool dragging = false;

    private void pic_MouseDown(object sender, MouseEventArgs e)
    {
        dragging = true;
        dragPoint = new Point(e.X, e.Y);
    }

    private void pic_MouseMove(object sender, MouseEventArgs e)
    {
        if (dragging)
            pic.Location = new Point(pic.Location.X + e.X - dragPoint.X, pic.Location.Y + e.Y - dragPoint.Y);
    }

    private void pic_MouseUp(object sender, MouseEventArgs e)
    {
        dragging = false;
    }

看，如果你拖拽一个你自己渲染的本地图片，这是不正确的..但是，由于在移动控件之后要移动该控件，因此新的移动坐标是相对于该控件的。因此，您不需要将dragPoint更新到移动时的最后一个位置。如果你只是移动一个正在渲染OnPaint的形状/图像，你必须在每次移动时更新拖动点。

如果需要，您可以进行一项改进，即仅在用户将光标移动到特定距离D时才开始拖动。例如，如下所示：

    Point dragPoint = Point.Empty;
    bool dragging = false;
    bool mouseDown = false;

    private void pic_MouseDown(object sender, MouseEventArgs e)
    {
        mouseDown = true;
        dragPoint = new Point(e.X, e.Y);
    }

    private void pic_MouseMove(object sender, MouseEventArgs e)
    {
        int deltaX = e.X - dragPoint.X;
        int deltaY = e.Y - dragPoint.Y;

        if (!dragging && mouseDown && deltaX * deltaX + deltaY * deltaY > 100)
            dragging = true;

        if (dragging)
            pic.Location = new Point(pic.Location.X + deltaX, pic.Location.Y + deltaY);
    }

    private void pic_MouseUp(object sender, MouseEventArgs e)
    {
        dragging = false;
        mouseDown = false;
    }

它检查用户是否已经将鼠标移动了10个像素(sqrt为100)。

如果你不想要一个全局的，你可以尝试实现你自己的行为系统，并创建一段可重用的代码，你可以附加到你想要移动的东西上。如下所示：

public class Behavior<T> where T : class 
{
    public T AssociatedObject
    {
        get;
        private set;
    }

    public Behavior(T associatedObject)
    {
        this.AssociatedObject = associatedObject;
    }

    public virtual void Attach() { }
    public virtual void Detach() { }
}

public class DragBehavior : Behavior<Control>
{
    Point dragPoint = Point.Empty;
    bool dragging = false;
    bool mouseDown = false;

    public DragBehavior(Control c) : base(c)
    {

    }

    public override void Attach()
    {
        AssociatedObject.MouseDown += new MouseEventHandler(control_MouseDown);
        AssociatedObject.MouseMove += new MouseEventHandler(control_MouseMove);
        AssociatedObject.MouseUp += new MouseEventHandler(control_MouseUp);
    }

    private void control_MouseUp(object sender, MouseEventArgs e)
    {
        dragging = false;
        mouseDown = false;
    }

    private void control_MouseMove(object sender, MouseEventArgs e)
    {
        int deltaX = e.X - dragPoint.X;
        int deltaY = e.Y - dragPoint.Y;

        if (mouseDown && deltaX * deltaX + deltaY * deltaY > 100)
            dragging = true;

        if (dragging)
            AssociatedObject.Location = new Point(AssociatedObject.Location.X + deltaX, AssociatedObject.Location.Y + deltaY);
    }

    private void control_MouseDown(object sender, MouseEventArgs e)
    {
        mouseDown = true;
        dragPoint = new Point(e.X, e.Y);
    }

    public override void Detach()
    {
        AssociatedObject.MouseDown -= new MouseEventHandler(control_MouseDown);
        AssociatedObject.MouseMove -= new MouseEventHandler(control_MouseMove);
        AssociatedObject.MouseUp -= new MouseEventHandler(control_MouseUp);
    }
}

public partial class Form1 : Form
{
    DragBehavior dragger;

    public Form1()
    {
        InitializeComponent();
        DoubleBuffered = true;

        dragger = new DragBehavior(pic);
        dragger.Attach();
    }       
}

也许这比“创建全局变量”(或者更像是在表单中创建成员变量)要好。=)

Answer 2

尝尝这个

int x_offset = 0; // any better to do this without having a global variable?
int y_offset = 0;
private void pic_MouseDown(object sender, MouseEventArgs e)
{
   PictureBox me = (PictureBox)sender;
   x_offset = e.X;
   y_offset = e.Y;
}

private void pic_MouseMove(object sender, MouseEventArgs e)
{
  if (e.Button == System.Windows.Forms.MouseButtons.Left)
  {
     PictureBox me = (PictureBox)sender;
     me.Left = e.X + me.Left - x_offset;
     me.Top = e.Y + me.Top - y_offset;
   }
}