问observable()不会按预期更新所选项目

EN

<select id="Catagories_CategoryId" data-bind="options: CategoryServiceTypes, 
    optionsText: 'Name',                        
    optionsCaption: 'Please select a Category...',                                        
    value: SelectedCategoryType">
</select>

obj.SelectedCategoryTypeHolder(obj.SelectedCategoryType()); //copy the old selected object
pager.LoadServiceTypesFromSvc(); //repop
ko.utils.arrayForEach(obj.CategoryServiceTypes(), function(data) {                                                        
    if (data.CategoryId() == obj.SelectedCategoryTypeHolder().CategoryId()) {
        obj.SelectedCategoryType(data);
        alert('selected ' + obj.SelectedCategoryType().Name()); //shows the name of the item I'm aiming for
    }
});