问react中使用formdata获取不了表单上传的文件？

"1、在react中有个form表单，包含text,radio和file,可是js代码创建formDate时获取不到file的信息，请问该怎么去获取。

2、代码如下：

render的代码：

<form ref="addForm" className="addForm" id="addForm" enctype="multipart/form-data" method="post">

<div className="formType" >

<label htmlFor="type" className="col-sm-1 control-label">物料类型</label>

<input type="radio" name="type" value="1" checked={this.state.type =="1"} onChange={this.handleChange} />图片

<input type="radio" name="type" value="2" checked={this.state.type =="2"} onChange={this.handleChange} />视频

</div>

<div className="formWidth">

<label htmlFor="materialWidth">物料宽</label>

<input type="text" id="materialWidth" name="width" value={this.state.width} onChange={this.handleChange} placeholder="物料宽度" />

</div>

<div className="formHeight">

<label htmlFor="materialHeight">物料高</label>

<input type="text" id="materialHeight" name="height" value={this.state.height} onChange={this.handleChange} placeholder="物料高度" />

</div>

<div className="formUpload">

<label htmlFor="uploadMaterial">上传文件</label>

<input ref="material" id="uploadMaterial" name="files" type="file" />

</div>

<div className="submit">

<button type="button" className="btn btn-success" onClick={(event)=>{this.handleSubmit(event)}}>提交</button>

</div>

</form>

js的代码：

getInitialState: function() {

　　　　return {

type: "",

width:"",

height:"",

"tab":"explain"

};

　　},

handleChange: function(event) {

var newState={};

newState[event.target.name]=event.target.name=="checked"?event.target.checked:event.target.value;

this.setState(newState);

　　},

handleSubmit: function(event){

var formDate = new FormData($("#addForm")[0]);

}