Winform+.Net6实现图片拖拽上传

前言

    如题，跟你使用过的某些拖拽上传的网站或者Web框架一样，将图片拖拽到指定位置后直接进行上传以及预览，减少找文件、操作的时间。本文主要使用WinformPictureBox控件+.Net6 WebApi实现。

开发环境：.NET Framework4.8+.Net6

开发工具：Visual Studio 2022

实现步骤

1. 创建自定义控件，继承自PictureBox,然后定义以下属性

   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());
                   }
                  
               }
           }
   

2. 处理拖拽事件

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);
        }

1. 重写OnPaint事件，做以下处理

   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));
               }
              
           }
   

1. 在Upload事件中完成上传

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());
        }

1. 后台接收文件

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";
        }

实现效果

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