IFormFile在Asp.Net Core WebAPI中始终为空

这是使用angularjs的方法：

vm.addFile = function () {     var fileUpload = $("#file").get(0);     var files = fileUpload.files;     var data = new FormData();     for (var i = 0; i < files.length ; i++) {         data.append(files[i].name, files[i]);     }     $http.post("/api/Files/", data, {         headers: { 'Content-Type': undefined },         transformRequest: angular.identity     }).success(function (data, status, headers, config) {     }).error(function (data, status, headers, config) {     });}

在网络Api中：

[HttpPost]public async Task<IActionResult> PostFile(){ //Read all files from angularjs FormData post request var files = Request.Form.Files; var strigValue = Request.Form.Keys; .....}

或像这样：

    [HttpPost]    public async Task<IActionResult>  PostFiles(IFormCollection collection)    {        var f = collection.Files; foreach (var file in f) {     //....  }    }