问angular2通过multipart/form-data文件上传出现问题？

file:File;
 selectedFileOnChanged($event) {
 console.log($event.target.value);
 this.readThis($event.target);
 var preview = document.querySelector('img');
 var uploadsFile = <HTMLInputElement>document.querySelector('input[type=file]');
 var file = uploadsFile.files[0];
 this.publish.upload(this.file).subscribe(data => {
 alert('ok');
 }, error => {
 console.log(JSON.stringify(error.json()));
 });
}

 upload(file){
 var headers = new Headers();
 headers.set('Content-Type','multipart/form-data');
 let data={file:file}
 return this.http
 .post('http://localhost:80/api/ImageUpload',data, {headers: headers})
 }