C# 在 FlowLayoutPanels 中拖放标签

Real Drag&Drop ist most useful between applications and maybe also between Forms.

假设您想在同一 Form 上的 FLPs 之间拖动 Labels，下面的代码应该可以帮助您进行操作..

Assuming you want to drag Labels between FLPs on the same Form, the code below should get you going..

它需要两个 FlowLayoutPanels，分别称为 FLP1 和 FLP2，并首先使用一些 Labels 对其进行初始化.

It takes two FlowLayoutPanels called FLP1 and FLP2 and starts by initializing them with a few Labels.

注意我添加到每个 Label 以模拟 Drag&Drop 动作的三个 鼠标事件！

Note the three mouse events I add to each Label to emulate a Drag&Drop action!

private void Form1_Load(object sender, EventArgs e)
{
    // create a few Label with varying Colors for testing..
    fillFLP(FLP1, 88);
    fillFLP(FLP2, 111);
}

void fillFLP(FlowLayoutPanel FLP, int cc)
{
    for (int i = 0; i < 24; i++)
    {
        Label l = new Label();
        // the next 3 lines optional and only are there for testing!
        l.AutoSize = false;      
        l.Text = FLP.Name + " " +  i.ToString("00");
        l.BackColor = Color.FromArgb(255, cc * 2 - i, 255 - 5 * i, cc + 5 * i); 
        // add controls and set mouse events:
        FLP.Controls.Add(l);
        l.MouseDown += l_MouseDown;
        l.MouseMove += l_MouseMove;
        l.MouseUp += l_MouseUp;
    }
}


// the currently moved Label:
Label mvLabel = null;

void l_MouseDown(object sender, MouseEventArgs e)
{
    // keep reference
    mvLabel = (Label)sender;
}

void l_MouseMove(object sender, MouseEventArgs e)
{
    // if we are dragging a label:
    if (mvLabel != null)
    {
        // mouse pos in window coords
        Point  mvPoint = this.PointToClient(Control.MousePosition);
        // the label is still in the FLP, so we start the drg action:
        if (mvLabel.Parent != this)
        {
            mvLabel.Parent = this;
            mvLabel.Location = mvPoint;
            mvLabel.BringToFront();
        }
        else
        {   
            // we are already in the form, so we just move
            mvLabel.Location = mvPoint;
        }
    }
}

void l_MouseUp(object sender, MouseEventArgs e)
{
    // are we over a FLP? and if so which?
    Point MP = Control.MousePosition;
    FlowLayoutPanel FLP = null;

    Point mLoc1 = FLP1.PointToClient(MP);
    Point mLoc2 = FLP2.PointToClient(MP);

    if (FLP1.ClientRectangle.Contains(mLoc1)) FLP = FLP1;
    else if (FLP2.ClientRectangle.Contains(mLoc2)) FLP = FLP2;
    else return;  // no! nothing we can do..

    // yes, now find out if we are over a label..
    // ..or over an empty area
    mvLabel.SendToBack();
    Control cc = FLP.GetChildAtPoint(FLP.PointToClient(MP));
    // if we are over the FLP we can insert at the beginning or the end:
    // int mvIndex = 0; // to the beginning
    int mvIndex = FLP.Controls.Count; // to the end
    // we are over a Label, so we insert before it:
    if (cc != null) mvIndex = FLP.Controls.IndexOf(cc);

    // move the Label into the FLP
    FLP.Controls.Add(mvLabel);
    // move it to the right position:
    FLP.Controls.SetChildIndex(mvLabel, mvIndex);
    // let go of the reference
    mvLabel = null;

}