C# winforms drag and drop

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Hi, trying to implement drag and drop
I have custom ToolBox class that simply iherits FlowLayoutPanel, and some picture boxes within. When user clicks on any of these picture boxes, it got copied and added to form's controls just on top of original. Then when user moves mouse around with left button pressed, that picture box should move along, but it don't. It works only if you release mouse button and then click again and move.

What I have tried:

C#

//want to mentioned that that's not the full code, only what is related to the question
 public partial class FigureToolBox : FlowLayoutPanel
 {

        public delegate void FigureSelected(PictureBox figurePicture,Point location);

        public event FigureSelected OnFigureSelect;
       
      //on mouse down of each picture box
      public void Figure_mouse_down(object c, MouseEventArgs e)
        {
            PictureBox pictureBox = c as PictureBox;

            PictureBox clonedPicture = new PictureBox();
            clonedPicture.SizeMode = PictureBoxSizeMode.AutoSize;
            clonedPicture.Image = pictureBox.Image;
            
            OnFigureSelect(clonedPicture, e.Location);

        }

     //some code
}
public partial class GameForm : Form
{
   Point point = new Point(); //start point of moving
   PictureBox draggedFig;


   public GameForm()
   {
     InitializeComponent();
     figureToolBox1.OnFigureSelect += FigureSelected;
   }

   private void FigureSelected(PictureBox box, Point location)
   {
            draggedFig = box;
            //just calculating  location of picture box in form's coords
            Point point = PointToClient(Cursor.Position);
            box.Left = (point.X- location.X);
            box.Top = (point.Y- location.Y);

            this.point = location;
            
            this.Controls.Add(draggedFig);
            draggedFig.BringToFront();

            draggedFig.MouseMove += DraggedFig_Move;
            draggedFig.Focus(); //thought it will help, but it won't
     }

    private void DraggedFig_Move(object sender, MouseEventArgs e){

            if (e.Button == MouseButtons.Left)
            {
                draggedFig.Left += e.X - point.X;
                draggedFig.Top += e.Y - point.Y;
            }
     }
}

Posted 22-Apr-19 4:20am

Member 14015063

Updated 23-Apr-19 8:48am

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Member 14015063 22-Apr-19 12:40pm

Finally got it. Just needed to disable toolbox before firing OnFigureSelect:
...
this.Enabled = false;
OnFigureSelect(clonedPicture, e.Location);

And then enable it back when mouse button released.

3 solutions

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Gerry Schmitz · Answer 1 · 2019-04-22T04:28:00

Solution 1

See where the "focus" is. If you can set the focus to the new PictureBox (which is probably what the second click does) it might work.

Posted 22-Apr-19 4:28am

Gerry Schmitz

Comments

Member 14015063 22-Apr-19 10:38am

Well, i tried, but it don't work. There's the line: draggedFig.Focus();
Or is there another way to focus on control?

[no name] 22-Apr-19 10:42am

You need to "trace" ALL the events. If setting it at one point doesn't work, it may at another. You have a particular scenario YOU need to understand in terms of what's going on, what behavior to "skip", etc. There is no "one size fits all". It's a question of FOCUS. Deal with it.

RickZeeland · Answer 2 · 2019-04-22T04:43:00

Solution 2

See CodeProject article here: Using the FlowLayoutPanel and Reordering with Drag and Drop[^]
And answer here: c# - How to drag images from a listview (together with an imageview) to pictureboxes? - Stack Overflow[^]

Posted 22-Apr-19 4:43am

RickZeeland

Updated 22-Apr-19 4:47am

v2

BillWoodruff · Answer 3 · 2019-04-23T08:49:00

First, be aware you are not using the WinForms Drag/Drop facility that has some sophisticated features for giving feedback while dragging, etc.

See if you get some ideas from this example, which like yours, is using a simple method

using System;
using System.Windows.Forms;

namespace YourNameSpace
{
    public partial class ToolBoxPanel : UserControl
    {
        public ToolBoxPanel()
        {
            InitializeComponent();
        }


        private void ToolBoxPanel_Load(object sender, EventArgs e)
        {
            parent = this.Parent as Form;
        }

        private PictureBox currentPB;

        private bool IsMouseUp = true;

        private CheckBox cb;

        private int cbCount = 0;

        private Form parent;

        // all PicturewBoxes in the UserControl use this Handler
        private void pictureBox_MouseDown(object sender, MouseEventArgs e)
        {
            currentPB = sender as PictureBox;

            switch (currentPB.Name)
            {
                case "pictureBox1":

                    cb = new CheckBox();

                    parent.Controls.Add(cb);
                    cb.Text = "CheckBox " + cbCount++;
                    cb.Show();
                    cb.BringToFront();

                    break;
            }

            IsMouseUp = false;
        }

        // all PicturewBoxes in the UserControl use this Handler
        private void pictureBox_MouseUp(object sender, MouseEventArgs e)
        {
            IsMouseUp = true;

            // cancel the drop if it's not over the Form ?
            if(this.DisplayRectangle.Contains
              (this.PointToClient
                (currentPB.PointToScreen(e.Location))))
            {
                parent.Controls.Remove(cb);
                cb.Dispose();
            }
        }

        // all PicturewBoxes in the UserControl use this Handler
        private void pictureBox_MouseMove(object sender, MouseEventArgs e)
        {
            if (IsMouseUp) return;

            // map the mouse location to the Parent Form
            cb.Location = parent.PointToClient(this.PointToScreen(e.Location));
        }
    }
}

Note: the moved Control in this example is not movable once it has been sited on the parent Form.