title: How to get a custom week value from a WeekPicker in a Form when I submit it
body: <p>I'm new to <code>ant-design-pro</code> and I'm writing a sample project to help my teammates get more efficient.</p>
  
  <p>Now I faced a problem, I can't get a custom format week value from a <code>WeekPicker</code> in a <code>Form</code>, the week value in the <code>Query String Parameters</code> is <code>week: "2019-12-11T08:45:42.884Z"</code> which is supposed to be <code>YYYYw</code> format, such as <code>week: 201950</code>.</p>
  
  <p>Here is how I defined the Form: </p>
  
  <pre><code>   ...
     &lt;Form onSubmit={this.handleSearch} layout="inline"&gt;
          ...
              &lt;FormItem label=""&gt;
                {getFieldDecorator('week')(&lt;WeekPicker placeholder="周" format={'YYYYw'} /&gt;)}
              &lt;/FormItem&gt;
          ...
     &lt;/Form&gt;
     ...
  </code></pre>
  
  <p>and here is the function code: </p>
  
  <pre><code>  handleSearch = (e: React.FormEvent) =&gt; {
      e.preventDefault();
  
      const { dispatch, form } = this.props;
  
      form.validateFields((err, fieldsValue) =&gt; {
        if (err) return;
        const values = {
          ...fieldsValue,
        }
        ...
        dispatch({
          type: 'listAndtableList/fetch',
          payload: values,
        });
      });
    } 
  </code></pre>
  
  <p>The form gets each field value automatically and it didn't notice that I defined a format in the <code>WeekPicker</code>, anyone can help?</p>