public class uploadAttachmentAssignmentController{  
    public Id recId{get;set;}
    public string fileName{get;set;}  
    public Blob fileBody{get;set;}
    public boolean isSaved{get;set;}  
    public Attachment myAttachment{get;set;}
    public uploadAttachmentAssignmentController(ApexPages.StandardController ctlr){  
        recId = ctlr.getRecord().Id;
        isSaved = false; 
    }          
    public PageReference UploadFile(){  
       isSaved = true; 
        if(fileBody != null && fileName != null)  
        {  
            Attachment myAttachment  = new Attachment();  
            myAttachment.Body = fileBody;  
            myAttachment.Name = fileName;  
            myAttachment.ParentId = recId;
            insert myAttachment; 
           // isSaved = true; 
            system.debug('############# value of isSaved'+isSaved);
        } 
          return null;  
    }   
}