Form inheritance - Servoy for Visual FoxPro Developers

How to use form inheritance

In this walkthrough we will create a sample in which we build a parent form that contains navigation logic. Additionally we will create customer- and employee subforms (subclasses based on frmNavigate) that make use of this changed behaviour.

We will use the example_data database in this walkthrough.

Create a new form
Set the form name to frmNavigate
Set the DataSource to -none-

Create a form without a datasource

Press Next
Uncheck the Place horizontal checkbox
Press Finish

Form dialog

Place several buttons along top of the form as in the image below
Set the text property of the buttons accordingly

Add navigation buttons

Select the New button
Doubleclick in the value area of the onAction event
In the dialog click the Create Form Method button
Type NewRecord and press Ok

Create NewRecord form method

Make sure that the newly created method is bound to the corresponding button as shown in the image below
Do the same for all other buttons and create the following methods: EditMode, FindMode, SaveChanges, CancelChanges, FirstRecord, PreviousRecord, NextRecord and LastRecord
Also add a SetFormReadOnly to the onShow event

Bind NewRecord method to the newButton

Now lets add some code. The first thing we want to take care of is making the form ReadOnly so that users can't make changes until they press the Edit button. Locate the SetFormReadOnly method and add the following code:

SetFormReadOnly methode code

This makes sure that the fields showing data are readonly and that changes to the data will not be save automatically. Next we want to add code to the NewRecord button:

New record code

Whenever the user wants to make changes to the data he will press the Edit button and we will enable the fields by adding only one line of code to the EditMode method:

Edit mode

To save changes we have to tell the databaseManager to do so. At the same time we want to disable the fields for further changes again:

Save changes

If the user wants to undo the changes (even to multiple records) then we will have to a rollback and make the fields readonly again:

Cancel changes

Finally we want to add the code for navigating through the records:

First record

Previous record

Next record

Last record

Ok, now we are finished with implementing our basic form navigation in the parent form frmNavigate. Now lets subclass it (Servoy calls this extending).

Select the example_data database in the Solution Explorer
In the List View locate the customers table and right-click it
From the popup-menu select Create new form

Enter frmSubCustomer as the form name
The datasource should be set to example_data.customers
Important! Set the extends property to frmNavigate.

Create frmSubCustomer based on frmNavigate

Select a few fields for editing
Uncheck the Place horizontal checkbox
Press the Finish button

Form dialog

Form designer frmSubCustomer

Notice the red dotted lines around the buttons in the form designer. This tells you which elements were inherited from the parent form. Now lets do the same for the employee form:

Select the example_data database in the Solution Explorer
In the List View locate the employees table and right-click it
From the popup-menu select Create new form

Enter frmSubEmployee as the form name
The datasource should be set to example_data.employees
Important! Set the extends property to frmNavigate.

Create frmSubEmployee based on frmNavigate

Select a few fields for editing
Uncheck the Place horizontal checkbox
Press the Finish button

Form dialog

Form designer frmSubEmployee

Start the application and play with both forms. As you can see we have now abstracted the forms navigation controls into the parent form frmNavigate. Little code was needed to change the default way Servoy handles data. In the subforms we didn't write any code at all!

Smart client

Conclusion

This walkthrough demonstrates Servoy's ease of use and it's powerful features at the same time!

The samples work in both the smart-client and in the web-client with one exception. In the web-client setting the form in Find-mode won't let you start a search. For this reason you may want to add a search button that starts the search in the web-client and is hidden in the smart-client. You may also want to add a delete button and use graphics on the buttons.