Cors跨域问题

运行程序debug以下就行了，后台程序报错，因为未对抛出的异常做任何处理，为了保护这些异常信息不被前端看到，你看到的就都会是这种500的错误，而且因为异常抛出的不会自动添加跨域的头，所以也会报跨域头的错误。所以建议就是：

1、debug看抛出了什么异常服务器内部错误的状态码是，问题就能解决了；

2、重写ExceptionFilterAttribute的OnException方法服务器内部错误的状态码是，对不同的exception返回不同的异常信息，比如文件不存在可以返回一个状态码为404的异常：

public override void OnException(ExceptionContext context)
{
    var exception = context.Exception;
    if (exception == null)// should never happen
    {
        return;
    }
    //todo: log the exception.
    context.Result = new ObjectResult(new { Message =         exception.Message });
    if (exception is KeyNotFoundException)
    {
        context.HttpContext.Response.StatusCode = 404;//Not Found
    }
    else if (exception is ArgumentException || exception is ArgumentNullException)
    {
        context.HttpContext.Response.StatusCode = 400;//Bad Request
    }
    else if (exception is NotImplementedException)
    {
        context.HttpContext.Response.StatusCode = 501; //Not Implemented
        context.Result = new ObjectResult(new { Message = "Not implemented." });
    }
    else if (exception is InvalidOperationException)
    {
        context.HttpContext.Response.StatusCode = 500;
    }
    else if (exception is MemberAccessException)
    {
        context.HttpContext.Response.StatusCode = 401;//Unauthorized
    }
    else// Other exception types you want to handle ... 
    {
context.HttpContext.Response.StatusCode = 500;
context.Result = new ObjectResult(new { Message = "An error has occured." });//Exceptions whose message should not be shown to users.
}
}