Winform+.Net6实现图片拖拽上传功能

private string _NullDesc;
        [Description("没有图像时的描述")]
        public string NullDesc { get { return _NullDesc; } set { _NullDesc = value; Invalidate(); } }
        private Font _NullDescFont;
        [Description("没有图像时的描述字体")]
        public Font NullDescFont { get { return _NullDescFont; } set { _NullDescFont = value; Invalidate(); } }
        private Color _NullDescFontColor;
        [Description("没有图像时的描述字体颜色")]
        public Color NullDescFontColor { get { return _NullDescFontColor; } set { _NullDescFontColor = value; Invalidate(); } }
        [Description("上传事件")]
        public event EventHandler Upload;
        public new Image Image
        {
            get
            {
                return base.Image;
            }
            set
            {
                base.Image = value;
                if (value != null)
                {
                    Upload?.Invoke(this, new EventArgs());
                }
            }
        }

protected override void OnDragEnter(DragEventArgs drgevent)
        {
            base.OnDragEnter(drgevent);
            if (drgevent.Data.GetDataPresent(DataFormats.FileDrop) || drgevent.Data.GetDataPresent(DataFormats.Bitmap))
            {
                drgevent.Effect = DragDropEffects.Copy;
            }
            else
            {
                drgevent.Effect = DragDropEffects.None;
            }
        }
        protected override void OnDragDrop(DragEventArgs drgevent)
        {
            base.OnDragDrop(drgevent);
            Image = GetImage(drgevent.Data);
        }

protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            Graphics g = e.Graphics;
            if (Image == null && BackgroundImage == null && !string.IsNullOrWhiteSpace(NullDesc))
            {
                SizeF sf = g.MeasureString(NullDesc, NullDescFont, Size);
                float x = (Width - sf.Width) / 2;
                float y = (Height - sf.Height) / 2;
                g.DrawString(NullDesc, Font, new SolidBrush(NullDescFontColor), new PointF(x, y));
            }
        }

  private async void PictureBoxEx1_Upload(object sender, EventArgs e)
        {
            HttpClient client = new HttpClient();
            MemoryStream memoryStream = new MemoryStream();
            Image img = (Image)pictureBoxEx1.Image.Clone();
            img.Save(memoryStream, img.RawFormat);
            memoryStream.Seek(0, SeekOrigin.Begin);
            MultipartFormDataContent content = new MultipartFormDataContent();
            StreamContent streamContent = new StreamContent(memoryStream);
            streamContent.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("form-data")
            {
                Name = "file",
                FileName = "upload" + GetExtension(img)
            };
            content.Add(streamContent);
            var result =await client.PostAsync("https://localhost:7075/Default/Upload", content);
            MessageBox.Show(await result.Content.ReadAsStringAsync());
        }

 public string Upload(IFormFile file)
        {
            string basePath = AppContext.BaseDirectory + "upload\\";
            if (file == null || file.Length == 0)
            {
                return "文件不可为空";
            }
            if (!Directory.Exists(basePath))
            {
                Directory.CreateDirectory(basePath);
            }
            string filter = Path.GetExtension(file.FileName);
            string fileName = DateTime.Now.Ticks + filter;
            string savePath = basePath + fileName;
            using var stream = new FileStream(savePath, FileMode.OpenOrCreate, FileAccess.ReadWrite);
            file.CopyTo(stream);
            return "上传成功";
        }