Problem: User needs to see the result of changes to a non-destructive job or query's parameters immediately following the change Pattern: Code that generates the results runs on a separate thread and is interrupted and restarted by a control module that subscribes to PropertyChanged events coming from a structure bound to the UI's controls Example: class JobCriteria : INotifyPropertyChanged{ public bool MinimumAge { get { return _minimumAge; } set { _minimumAge = value; PropertyChanged(this, new PropertyChangedEventArgs("MinimumAge")); } } // ... other properties ...}// In code for the UI controller...void JobCriteria_PropertyChanged(object sender, PropertyChangedEventArgs e){ JobCriteria critera = sender as JobCriteria; if (ResultsWorker != null && ResultsWorker.IsBusy) ResultsWorker.CancelAsync(); // ... clear the UI of old results ... ResultsWorker = new BackgroundWorker(); // ... setup BackgroundWorker ... ResultsWorker.RunWorkerAsync(criteria);}void ResultsWorker_DoWork(object sender, DoWorkEventArgs e){ BackgroundWorker myWorker = sender as BackgroundWorker; JobCriteria criteria = e.Argument as JobCriteria; while (!myWorker.CancellationPending) { // ... compute results ... foreach (InterestingDataType result in theResults) myWorker.ReportProgress(0, result); }}void ResultsWorker_ProgressChanged(object sender, ProgressChangedEventArgs e){ InterestingDataType result = e.UserState as InterestingDataType; // ... update the UI with the new result}Discussion: The user will be able to change the criteria for the job--be it a search or some other non-destructive operation--and see the display of results clear and begin rebuilding instantaneously. In code, the JobCriteria_PropertyChanged event handler is subscribed to the PropertyChanged event of an instance of JobCriteria, which is the same instance bound to the controls in the UI. Upon handling a PropertyChanged event it halts any current background thread that may already be running, clears the UI of any old results, and then starts a new BackgroundWorker thread to act upon the new critera. New results are marshaled back into the UI's thread by raising the ReportProgress event. |