+Writing new controls is often desired by advanced programmers, because they want to reuse the code that they write for dealing with complex presentation and user interactions. +
++In general, there are two ways of writing new controls: composition of existing controls and extending existing controls. They all require that the new control inherit from TControl or its child classes. +
+Composition is the easiest way of creating new controls. It mainly involves instantiating existing controls, configuring them and making them the constituent components. The properties of the constituent components are exposed through subproperties. +
++One can compose a new control in two ways. One is to override the TControl::createChildControls() method. The other is to extend TTemplateControl (or its child classes) and write a control template. The latter is easier to use and can organize the layout constituent compoents more intuitively, while the former is more efficient because it does not require parsing of the template. +
++As an example, we show how to create a labeled textbox called LabeledTextBox using the above two approaches. A labeled textbox displays a label besides a textbox. We want reuse the PRADO provided TLabel and TTextBox to accomplish this task. +
- ++We need two files: a control class file named LabeledTextBox.php and a control template file named LabeledTextBox.tpl. Both must reside under the same directory. +
++Like creating a PRADO page, we can easily write down the content in the control template file. +
++The above template specifies a TLabel control named Label and a TTextBox control named TextBox. We would to expose these two controls. This can be done by defining a property for each control in the LabeledTextBox class file. For example, we can define a Label property as follows, +
++In the above, the method call to ensureChildControls() ensures that both the label and the textbox controls are created (from template) when the Label property is accessed. The TextBox property can be implemented similarly. +
++For a composite control as simple as LabeledTextBox, it is better to create it by extending TControl and overriding the createChildControls() method, because it does not use templates and thus saves template parsing time. +
++Complete code for LabeledTextBox is shown as follows, +
++To use LabeledTextBox control, first we need to include the corresponding class file. Then in a page template, we can write lines like the following, +
++In the above, Label.Text is a subproperty of LabeledTextBox, which refers to the Text property of the Label property. For other details of using LabeledTextBox, see the above online examples. +