WinForms Task Anime Demo

MainForm.cs

using System;
using System.Drawing;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WinFormTaskAnimeDemo
{
    public sealed class MainForm : Form
    {
        Control DraggingControl;
        Point DraggingStartLocation;
        Task MoveBackAnime;

        [STAThread]
        static void Main()
        {
            Application.SetHighDpiMode(HighDpiMode.SystemAware);
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new MainForm());
        }

        public MainForm()
        {
            var pictureBox1 = new PictureBox
            {
                Image = Icon.ToBitmap(),
                Size = new Size(128, 128),
                SizeMode = PictureBoxSizeMode.StretchImage,
                BackColor = Color.LightSkyBlue,
            };
            pictureBox1.MouseDown += Control_MouseDown;
            pictureBox1.MouseMove += Control_MouseMove;
            pictureBox1.MouseUp += Control_MouseUp;

            var pictureBox2 = new PictureBox
            {
                Image = Icon.ToBitmap(),
                Size = new Size(128, 128),
                SizeMode = PictureBoxSizeMode.StretchImage,
                BackColor = Color.LightSeaGreen,
                Location = pictureBox1.Location + pictureBox1.Size,
            };
            pictureBox2.MouseDown += Control_MouseDown;
            pictureBox2.MouseMove += Control_MouseMove;
            pictureBox2.MouseUp += Control_MouseUp;

            var tip = new ToolTip();
            tip.SetToolTip(pictureBox1, "Drag me !");
            tip.SetToolTip(pictureBox2, "Drag me !");

            var panel = new Panel
            {
                Dock = DockStyle.Fill,
                BackColor = Color.LightGray,
            };
            panel.Controls.Add(pictureBox1);
            panel.Controls.Add(pictureBox2);
            panel.Resize += Panel_Resize;

            SuspendLayout();
            Text = "WinForms Task Anime Demo";
            Controls.Add(panel);
            ClientSize = new Size(640, 480);
            ResumeLayout(false);
        }

        void Control_MouseDown(object sender, MouseEventArgs e)
        {
            // 如果有動畫而且還沒跑完就不處理事件
            if (MoveBackAnime != null && !MoveBackAnime.IsCompleted) return;

            // 把觸發事件的控制項跟滑鼠位置記錄下來
            DraggingControl = sender as Control;
            DraggingStartLocation = e.Location;

            // 把最新被點的移到最前面顯示
            DraggingControl.Parent.Controls.SetChildIndex(DraggingControl, 0);
        }

        void Control_MouseMove(object sender, MouseEventArgs e)
        {
            // 如果有動畫而且還沒跑完就不處理事件
            if (MoveBackAnime != null && !MoveBackAnime.IsCompleted) return;
            // 如果觸發事件的控制項不是原先觸發 MouseDown 的控制項就不處裡事件
            if (sender != DraggingControl) return;

            // 算出滑鼠的偏移量
            var mouseOffset = e.Location.Subtract(DraggingStartLocation);

            // append 給控制項
            DraggingControl.Location = DraggingControl.Location.Add(mouseOffset);
        }

        void Control_MouseUp(object sender, MouseEventArgs e)
        {
            // 如果有動畫而且還沒跑完就不處理事件
            if (MoveBackAnime != null && !MoveBackAnime.IsCompleted) return;
            // 如果觸發事件的控制項不是原先觸發 MouseDown 的控制項就不處裡事件
            if (sender != DraggingControl) return;

            // 如果控制項已經移出父控制項範圍就啟動動畫
            if (!DraggingControl.IsInsideParent())
                MoveBackAnime = DraggingControl.MoveBackInsideParentAsync();

            // 清除觸發事件的控制項
            DraggingControl = null;
        }

        void Panel_Resize(object sender, EventArgs e)
        {
            if (MoveBackAnime != null && !MoveBackAnime.IsCompleted) return;

            var control = (sender as Control);
            if (control == null) return;
            var animations = control.Controls
                    .OfType<Control>()
                    .Where(c => !c.IsInsideParent())
                    .Select(c => c.MoveBackInsideParentAsync())
                    .ToArray();
            MoveBackAnime = Task.WhenAll(animations);
        }
    }

    static class Extensions
    {
        public static Point Add(this Point p1, Point p2) => new Point(p1.X + p2.X, p1.Y + p2.Y);

        public static Point Subtract(this Point p1, Point p2) => new Point(p1.X - p2.X, p1.Y - p2.Y);

        /// <summary>
        /// 判斷控制項的螢幕範圍是否在父控制項的螢幕範圍內
        /// </summary>
        public static bool IsInsideParent(this Control control)
        {
            var parent = control.Parent;
            if (parent == null) return false;
            var parentBounds = parent.RectangleToScreen(Rectangle.Empty);
            var controlBounds = control.RectangleToScreen(Rectangle.Empty);
            return parentBounds.Contains(controlBounds);
        }

        /// <summary>
        /// 將控制項移回父控制項的範圍內
        /// </summary>
        public static async Task MoveBackInsideParentAsync(this Control control)
        {
            var parent = control.Parent;
            if (parent == null) return;
            while (!control.IsInsideParent())
            {
                var offset = new Point();

                if (parent.Width > control.Width)
                {
                    if (control.Left < 0) offset.X += 1;
                    if (control.Right > parent.Width) offset.X -= 1;
                }
                else
                    offset.X = -control.Left;

                if (parent.Height > control.Height)
                {
                    if (control.Top < 0) offset.Y += 1;
                    if (control.Bottom > parent.Height) offset.Y -= 1;
                }
                else
                    offset.Y = -control.Top;

                if (offset == Point.Empty)
                    return;

                control.Location = control.Location.Add(offset);
                await Task.Yield();
            }
        }
    }
}