You can use plugin as suggested by one fellow here or you can use JavaScript to recalculate it for you and bring you the updated results on the spot !
For later approach, you can use the code below ...
function CalculateRollupField(EntityName, recGuid, RollUpFieldName)
{
recGuid = recGuid.replace("{", "").replace("}", ""); // String Guid
var HttpReq = new XMLHttpRequest();
HttpReq.open(this.method, this.url, true); // Need this to initiate the request
HttpReq.setRequestHeader("OData-Version", "4.0");
HttpReq.setRequestHeader("OData-MaxVersion", "4.0");
// Double Check your API URL, may differ for v9.0
HttpReq.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v8.2/" + "CalculateRollupField(Target=@p1,FieldName=@p2)?" + "@p1={'@odata.id':'" + EntityName + "(" + recGuid + ")'}&" + "@p2='" + RollUpFieldName + "'", true);
HttpReq.onreadystatechange = function ()
{
if (this.readyState === 4)
{
HttpReq.onreadystatechange = null;
if (this.status === 200)
{
var results = JSON.parse(this.response);
}
else
{
Xrm.Utility.alertDialog(this.statusText);
}
}
};
HttpReq.send(JSON.stringify({}));
}
Once you trigger the above JS function, you can retrieve the updated value via JS API call and use XRM commands to replace the updated value in the form for better user experience
