<div id="FormContent">
        <form id="FormUpload"
        enctype="multipart/form-data" method="post">
          <span class="btn btn-success fileinput-button">
            <i class="glyphicon glyphicon-plus"></i>
            <span>Add files...</span>
            <input type="file"
            name="UploadedFile" id="UploadedFile" />
          </span>
          <button class="btn btn-primary start"
          type="button" id="Submit_btn">
            <i class="glyphicon glyphicon-upload"></i>
            <span>Start upload</span>
          </button>
          <button class="btn btn-warning cancel"
          type="button" id="Cancel_btn">
            <i class="glyphicon glyphicon-ban-circle"></i>
            <span>close</span>
          </button>
        </form>
        <div class="progress CustomProgress">
          <div id="FileProgress"
          class="progress-bar" role="progressbar"
      aria-valuenow="" aria-valuemin=""
      aria-valuemax="" style="width %;">
            <span></span>
          </div>
        </div>
        <div class="InfoContainer">
          <div id="Imagecontainer"></div>
          <div id="FileName" class="info">
          </div>
          <div id="FileType" class="info">
          </div>
          <div id="FileSize" class="info">
          </div>
        </div>
      </div>

 function singleFileSelected(evt) {
     //var selectedFile = evt.target.files can use this or select input file element 
     //and access it's files object
     var selectedFile = ($("#UploadedFile"))[].files[];//FileControl.files[];
     if (selectedFile) {
       var FileSize = ;
       var imageType = /image.*/;
       if (selectedFile.size > ) {
         FileSize = Math.round(selectedFile.size * / ) / + " MB";
      }
      else if (selectedFile.size > ) {
        FileSize = Math.round(selectedFile.size * / ) / + " KB";
      }
      else {
        FileSize = selectedFile.size + " Bytes";
      }
      // here we will add the code of thumbnail preview of upload images
      
      $("#FileName").text("Name " + selectedFile.name);
      $("#FileType").text("type " + selectedFile.type);
      $("#FileSize").text("Size " + FileSize);
    }
  }

 if (selectedFile.type.match(imageType)) {
        var reader = new FileReader();
        reader.onload = function (e) {
          $("#Imagecontainer").empty();
          var dataURL = reader.result;
          var img = new Image()
          img.src = dataURL;
          img.className = "thumb";
          $("#Imagecontainer").append(img);
        };
        reader.readAsDataURL(selectedFile);
      }

function UploadFile() {
     //we can create form by passing the form to Constructor of formData object
     //or creating it manually using append function 
     //but please note file name should be same like the action Parameter
     //var dataString = new FormData();
     //dataString.append("UploadedFile", selectedFile);
   
     var form = $('#FormUpload')[];
     var dataString = new FormData(form);
    $.ajax({
      url '/Uploader/Upload', //Server script to process data
      type 'POST',
      xhr function () { // Custom XMLHttpRequest
        var myXhr = $.ajaxSettings.xhr();
        if (myXhr.upload) { // Check if upload property exists
          //myXhr.upload.onprogress = progressHandlingFunction
          myXhr.upload.addEventListener('progress', progressHandlingFunction, 
          false); // For handling the progress of the upload
        }
        return myXhr;
      },
      //Ajax events
      success successHandler,
      error errorHandler,
      completecompleteHandler,
      // Form data
      data dataString,
      //Options to tell jQuery not to process data or worry about content-type.
      cache false,
      contentType false,
      processData false
    });
  }

function progressHandlingFunction(e) {
     if (e.lengthComputable) {
       var percentComplete = Math.round(e.loaded * / e.total);
       $("#FileProgress").css("width", 
       percentComplete + '%').attr('aria-valuenow', percentComplete);
       $('#FileProgress span').text(percentComplete + "%");
     }
     else {
       $('#FileProgress span').text('unable to compute');
    }
  }

 public JsonResult Upload(HttpPostedFileBase uploadedFile)
       {
         if (uploadedFile != null && uploadedFile.ContentLength > )
         {
           byte[] FileByteArray = new byte[uploadedFile.ContentLength];
           uploadedFile.InputStream.Read(FileByteArray, , uploadedFile.ContentLength);
           Attachment newAttchment = new Attachment();
          newAttchment.FileName = uploadedFile.FileName;
          newAttchment.FileType = uploadedFile.ContentType;
          newAttchment.FileContent = FileByteArray;
          OperationResult operationResult = attachmentManager.SaveAttachment(newAttchment);
          if (operationResult.Success)
          {
            string HTMLString = CaptureHelper.RenderViewToString
            ("_AttachmentItem", newAttchment, this.ControllerContext);
            return Json(new
            {
              statusCode = ,
              status = operationResult.Message,
              NewRow = HTMLString
            }, JsonRequestBehavior.AllowGet);
          }
          else
          {
            return Json(new
            {
              statusCode = ,
              status = operationResult.Message,
              file = uploadedFile.FileName
            }, JsonRequestBehavior.AllowGet);
          }
        }
        return Json(new
        {
          statusCode = ,
          status = "Bad Request! Upload Failed",
          file = string.Empty
        }, JsonRequestBehavior.AllowGet);
      }

 <div id="drop_zone">Drop images Here</div>

 function MultiplefileSelected(evt) {
     evt.stopPropagation();
     evt.preventDefault();
     $('#drop_zone').removeClass('hover');
     selectedFiles = evt.target.files || evt.dataTransfer.files;
     if (selectedFiles) {
       $('#Files').empty();
       for (var i = ; i < selectedFiles.length; i++) {
         DataURLFileReader.read(selectedFiles[i], function (err, fileInfo) {
          if (err != null) {
            var RowInfo = '<div id="File_' + i + '" 
            class="info"><div class="InfoContainer">' +
                    '<div class="Error">' + err + '</div>' +
                   '<div data-name="FileName" 
                   class="info">' + fileInfo.name + '</div>' +
                   '<div data-type="FileType" 
                   class="info">' + fileInfo.type + '</div>' +
                   '<div data-size="FileSize" 
                   class="info">' + fileInfo.size() + 
                   '</div></div><hr/></div>';
            $('#Files').append(RowInfo);
          }
          else {
            var image = '<img src="/UploadFiles/2021-04-02/' + fileInfo.fileContent + 
            '">

在该方法中，将选择和拖拽文件操作的变量设置为全局变量selectedFiles，然后扫描 selectedfiles中的每个文件，将从 DataURLreader对象中调用Read 方法读取文件。
DataURLreader对象可调用read方法，并将File对象和回调方法作为read方法参数，在上述方法中我们创建了FileReader，并修改了FileReader的Onload和onerror回调函数。调用 readAsDataURL 方法来读文件。
新建FileInfo对象包括了所有的文件信息及内容。


 var DataURLFileReader = {
     read function (file, callback) {
       var reader = new FileReader();
       var fileInfo = {
         name file.name,
         type file.type,
         fileContent null,
         size function () {
           var FileSize = ;
          if (file.size > ) {
            FileSize = Math.round(file.size * / ) / + " MB";
          }
          else if (file.size > ) {
            FileSize = Math.round(file.size * / ) / + " KB";
          }
          else {
            FileSize = file.size + " bytes";
          }
          return FileSize;
        }
      };
      if (!file.type.match('image.*')) {
        callback("file type not allowed", fileInfo);
        return;
      }
      reader.onload = function () {
        fileInfo.fileContent = reader.result;
        callback(null, fileInfo);
      };
      reader.onerror = function () {
        callback(reader.error, fileInfo);
      };
      reader.readAsDataURL(file);
    }
  };


使用拖拽操作选择


由于大部分浏览器现在已经执行拖拽操作，为了实现拖拽操作，在drop_zone 元素中添加dragover和drop事件。
         var dropZone = document.getElementById('drop_zone');

         dropZone.addEventListener('dragover', handleDragOver, false);

         dropZone.addEventListener('drop', MultiplefileSelected, false);

         dropZone.addEventListener('dragenter', dragenterHandler, false);

         dropZone.addEventListener('dragleave', dragleaveHandler, false);
当文件拖到目标位置时触发dragover事件，在以下代码中，我们修改了默认浏览器及datatransfer的dropEffect 属性，代码如下：


  function handleDragOver(evt) {
     evt.preventDefault();
     evt.dataTransfer.effectAllowed = 'copy';
     evt.dataTransfer.dropEffect = 'copy';
   }


接着在MultiplefileSelected中添加drop事件来处理文件drop操作。
大部分功能已经完善，现在需要添加“上传按钮”，通过Onclick事件来调用UploadMultipleFiles方法。
该方法与上文提到的Uploadfile方法类似，不同的是手动验证formdata对象值。


   function UploadMultipleFiles() {
     // here we will create FormData manually to prevent sending mon image files
     var dataString = new FormData();
     //var files = document.getElementById("UploadedFiles").files;
     for (var i = ; i < selectedFiles.length; i++) {
       if (!selectedFiles[i].type.match('image.*')) {
         continue;
       }
      }
  // AJAX Request code here
  }


接下来添加服务器端处理代码，与上文添加的代码类似，需要做的就是接受一系列的文件列表，如下：
  public JsonResult UplodMultiple(HttpPostedFileBase[] uploadedFiles)


确保 HttpPostedFileBase 数组名称与append 方法中的名称相同，只有这样，MVC才能映射到文件数组中。
 public JsonResult UplodMultiple(HttpPostedFileBase[] uploadedFiles)

  dataString.append("uploadedFiles", selectedFiles[i]); 


上传大文件


为了允许上传大文件，如果使用的是 IIS7及以上版本，需要修改Web.config 文件，添加以下代码：


<system.webServer>
      <security>
           <requestFiltering>
                <requestLimits maxAllowedContentLength="" />
           </requestFiltering>
      </security>
   </system.webServer>
   <httpRuntime targetFramework="." maxRequestLength=""/>


到这里所有的功能就可以实现了，而且最大可上传2GB的文件。
以上内容就是小编给大家介绍的MVC中基于Ajax和HTML5实现文件上传功能，希望对大家有所帮助。