pdf417 c# source Saving the Data in Visual C#

Generation PDF417 in Visual C# Saving the Data

Saving the Data
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When the user clicks the Save button, the data needs to be saved. This is the most complex bit of processing the UI developer should have to write. The complexity comes because the object may be updated during the update process, and it is possible for the update process to fail part of the way through possibly leaving the object in an invalid or indeterminate state. For instance, suppose Jeff edits a number of roles in the Roles object. And suppose Marie has edited the last role in the list and saved her change. When Jeff saves his changes, all the data will be saved (updating the timestamp values in each Role object) until the update process hits that last
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CHAPTER 9 s WINDOWS FORMS UI
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role. At that point, a concurrency issue is detected and an exception is thrown. The database transaction handles rolling back the database to a valid state, but all those Role objects now have invalid timestamp values in memory. Somehow the Roles object needs to be reset to the state it was in before Save() was called. Another issue occurs if the data portal is configured to run locally in the client process. In that case, the object is not serialized to a server, but rather is updated in place on the client. It is possible that the business object could raise PropertyChanged or ListChanged events while it is being updated, causing the UI to refresh during the data update process. Not only does that incur performance costs, but sometimes code in the UI might respond to those events in ways that cause bugs. To avoid these issues, the following process is followed: 1. Turn off events from the BindingSource controls. 2. Clone the business object. 3. Save the clone of the business object. 4. Rebind the BindingSource controls to the new object returned from Save(), if necessary. 5. Turn on events from the BindingSource controls. Turning off and on the events from the BindingSource controls ensures that any events from the data source won t be cascaded up to the UI during the update process. This is important, because otherwise an exception will occur when rebinding the BindingSource controls to the new object returned from Save(). As you ll see, this rebinding requires that the DataSource property first be set to null, which of course isn t a valid data source for the UI. The reason for cloning the business object is so an exact copy of the object can be saved to the database. It is this exact copy of the object that has its fields changed during the update process. If the update fails, then the original object remains intact and unchanged, but if the update succeeds, then the Save() method returns the successfully updated version of the object, including any new field values. Here s the code for the Save button on the RolesEdit user control: private void SaveButton_Click(object sender, EventArgs e) { this.rolesBindingSource.RaiseListChangedEvents = false; Roles temp = _roles.Clone(); try { _roles = temp.Save(); this.Close(); } catch (Csla.DataPortalException ex) { MessageBox.Show(ex.BusinessException.ToString(), "Error saving", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); } catch (Exception ex) { MessageBox.Show(ex.ToString(), "Error saving", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); } finally { this.rolesBindingSource.RaiseListChangedEvents = true; } }
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CHAPTER 9 s WINDOWS FORMS UI
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The first line of code turns off event processing for the BindingSource control: this.rolesBindingSource.RaiseListChangedEvents = false; You would do this for every BindingSource control on the form if there were more than one. In ProjectEdit, for instance, there are two such controls bound to editable data. The next line of code creates a clone of the business object: Roles temp = _roles.Clone(); This is easily done, since all CSLA .NET business objects automatically support the Clone() method. Remember that this method copies the object and all child objects it contains. In this case, it copies the Roles object and all the Role objects in the collection. Then the copy of the object is saved: _roles = temp.Save(); Notice that the result of the Save() method is stored in the original _roles field, which overwrites the original value. If no exception occurs during the Save() call, the original object is replaced by the resulting updated object. Remember that most insert and update operations do change the object s data, at least updating the timestamp values for concurrency. If the user control was not immediately closed, you would rebind the BindingSource object to the new business object returned from the Save() method by adding these lines of code immediately after the Save() method call: this.rolesBindingSource.DataSource = null; this.rolesBindingSource.DataSource = _roles; You can t simply set the DataSource property to a new object. You must first set the property to null, and then to the new object. If you don t do this, the BindingSource will not bind to the new object and will silently remain bound to the old object, resulting in hard-to-debug problems in your application. In this case, the form is closed immediately upon successfully saving the data, so the UI is not rebound. Instead, the user control s Close() method is called: this.Close(); The Save() call and closing of the user control (or rebinding of the BindingSource control) occurs in a try block. If an exception occurs during the Save() call, the _roles field will not be set to a new value, meaning it will retain the original value it had to start with. Additionally, in the case of an exception, the user control isn t closed (or if the UI is being rebinded, that rebinding won t occur). This means that the BindingSource control will still be bound to the original, unchanged, object. This is exactly the desired behavior, since it means that the UI controls are still bound to an object in a valid state (even though it apparently can t be saved for some reason). The catch blocks contain code to display the exception details to the user as discussed earlier. Finally, whether an exception occurs or not, event handling is reenabled for the BindingSource control: this.rolesBindingSource.RaiseListChangedEvents = true; This must occur for data binding to behave properly, either against the newly updated object, or the original object in the case of an exception.
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