处理$http AngularJS返回数据

这是AngularJS中的客户端（运行良好）：

$scope.ajaxLogin = function(){
    var fn = document.getElementById("username").value;
    var pw = document.getElementById("password").value;
    $http({
        url: "myurl", 
        method: "POST",
        headers: {'Content-Type': 'application/x-www-form-urlencoded'},
        data: { username: fn, password: pw }
    }).success(function(data, status, headers, config) {
        // this callback will be called asynchronously
        // when the response is available
        $scope.showAlertError();
    }).error(function(data, status, headers, config) {
        // called asynchronously if an error occurs
        // or server returns response with an error status.
        $scope.showAlertError();
    });
};

我希望只有在用户和密码匹配的情况下才能成功。服务器端：

if ($result=mysqli_query($con,$sql))
{     
    $rowcount=mysqli_num_rows($result);
    printf($rowcount);
    mysqli_free_result($result);
}

在AngularJS之前，我使用了普通的AJAX处理。我以前是这样做的：

  function ajax_post(){
      // Create our XMLHttpRequest object
      var hr = new XMLHttpRequest();
      // Create some variables we need to send to our PHP file
      var url = "myurl";
      var fn = document.getElementById("username").value;
      var ln = document.getElementById("password").value;
      var vars = "username="+fn+"&password="+ln;
      hr.open("POST", url, true);
      // Set content type header information for sending url encoded variables in the request
      hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
      // Access the onreadystatechange event for the XMLHttpRequest object
      hr.onreadystatechange = function() {
        if(hr.readyState == 4 && hr.status == 200) {
          var return_data = hr.responseText;
        if(return_data=="1"){
          console.log("this is return data"+return_data);
        }else{
          ons.notification.alert({message: 'Login Failed!'});
        }
        }
      }
      // Send the data to PHP now... and wait for response to update the status div
      hr.send(vars); // Actually execute the request
  }

如何将其与AngularJS一起使用？我尝试在成功处理程序中放入类似的代码，但它总是转到else块。