/// <summary>创建 <see cref="T:System.Net.Http.MultipartContent" /> 类的新实例。</summary>
/// <param name="subtype">多部分内容的子类型。</param>
/// <exception cref="T:System.ArgumentException">
/// <paramref name="subtype" /> 为 <see langword="null" /> 或者只包含空格字符。</exception>
public MultipartContent(string subtype)
: this(subtype, MultipartContent.GetDefaultBoundary())
{
}
/// <summary>创建 <see cref="T:System.Net.Http.MultipartContent" /> 类的新实例。</summary>
public MultipartContent()
: this("mixed", MultipartContent.GetDefaultBoundary())
{
}
