Template Properties (called Template Parameters) allow each template instance to reference different data. Because the primary use of templates are the ease of maintaining repeated user interface elements, correct use of Template Parameters is very important. This is very similar to the concept of Parameterized Popup Windows. In that case, any Custom property on the Root Container of the window is used as a parameter, and is passed into the window when it is opened. With Templates, you have a property in the root of the master template that is exposed when you drop a Template Instance on a window.
Template Parameters and Internal Properties
When you open the Custom Properties window (right-click the checkered-box of the template and select Customizers > Custom Properties), you'll notice it is different than the Custom Properties of all other components. There are two kinds of custom properties here, as follows:
- Template Parameters
These parameters appear on each template instance, allowing each instance to be configured differently. Commonly, this is some sort of indirection. For example, if you have a template representing motors, you might have MotorNumber as a parameter property. Then you can use that property as an indirection variable in other bindings within the template. Parameter properties are not bindable from within the template master design. When you use the template to create a template instance, the property becomes bindable. This ensures that the property only has a single binding configured for it.
These properties cannot be used as parameters in your instances. They show up when designing the template master, but it does not show up on the template instances. Internal properties are bindable from within the template master design. These properties are intended to be used for the internal workings of the template.
Indirection and UDT Tags
There are two primary ways to achieve indirection when using templates. Let's continue to use the example of a motor. Your system has many motors in it, and your template is used to display the status of the motors and control the motor's running mode. The goal is to be able to drop instances of the template onto your windows, and configure them in a single step to point to the correct motor's Tags.
If the Tags representing the datapoints of each motor are arranged in an orderly way in folders or with a consistent naming convention, you can use standard indirection to configure your template. You can add a parameter such as MotorNum to the template. Then you configure the contents of the template using indirect Tag binding, where the value of MotorNum is used for the indirection.
If your motors are represented by a User Defined Type (UDT), you can save some effort and use a property of that type directly. Make your indirection property the same type as your custom data type. Then inside your template, you can use simple property bindings to create a link to the members of the UDT. When you create a template instance, you can simply bind that property directly to the correct Motor Tag, and all of the sub-Tags of motor are correctly mapped through the property bindings.
The Drop Target Parameter
When you specify parameters in the Custom Properties window (right-click the checkered-box of the template and select Customizers > Custom Properties), you can set one of the parameters as the Drop Target. This allows you to drop a Tag of that type onto your template instances or onto a window to facilitate even quicker binding. For example, let's say that you have a parameter that is an integer and you've made it the drop target. If you drop an integer Tag onto a window, your template appears in the menu dropdown list of components which is displayed. Choosing your template creates a template instance and binds that parameter to the Tag.
This also works for UDT Tags. Let's say you have a custom data type called Motor and a template with a Motor-typed parameter set as the drop target. If you drop a motor Tag onto a window, it creates an instance of your template automatically. If you have more than one template configured with Motor drop targets, you have to choose which template to use.
Accessing Components Inside a Template Instance
When working with a Template Instance, the components inside that instance or normally hidden, and otherwise inaccessible. However, you can access these components via scripting. It helps to think of Template Instances as multi-layer containers. In most cases, users interact with only the Outer Layer, which contains the Template parameters, and the other default Template Instance properties. A Python script can access the Inner Layer, which then provides access to the components within.
A script can traverse to the Inner Layer from the Outer Layer with a
myTemplate = event.source.parent.getComponent('MyTemplate') # The '0' in the first getComponent call effectively refers to an index value of a component, which happens to be the Inner Layer. myTemplate.getComponent(0)
From the Inner Layer, a script can then call
getComponent again to access any components within. Assuming a Template with a Label component named "Label", we could access the Text property with the following:
myTemplate = event.source.parent.getComponent('MyTemplate') print myTemplate.getComponent(0).getComponent('Label').text