#Xojo properties code

On the other hand, we could use the Get on the property to retrieve the associated value using a predefined format.

#Xojo properties code

The magic behind Set and Getīehind of the sugar syntax they provide, the real power found in Computed Properties, when compared with regular ones, resides in the code that we can write on both, and that will be executed just before we retrieve the property value or just before we make a new assignation to it.įollowing with our example, if we would be using the property to store a person name, we could use Set on such property to provide a default value if the received one is an empty string: Set (Value As String) If Value = '' then mMyProperty = 'New User' At the same time, the scope will change to Private too. Add a new property, select it from the Project Browser, access the contextual menu and select the ‘ Convert to Computed Property‘ option, as showed in the following screenshot:Īs result, you’ll find that Xojo’s IDE has included the wrapper previously seen, modifying the original property’s name to include the “m” character as prefix. In fact, the way you can more clearly see the relationship between a regular property and the Calculated Property wrapper is by defining the regular property in first place. The only way to get and/or set its value would be from the Computed Property methods previously created. This way we will be sure that no other object can directly access the property.

This is something we can fix very easily just a matter of adding a new property and defining its scope as private. The property itself doesn’t exists yet, just this wireframe or umbrella! When we create a new Computed Property this way, we are creating the wrapper but still have to define the real container (the property itself) in charge to store the values processed by Set and Get. While ‘Set’ is the one automatically invoked every time we want to assign a new value to the property, using, for instance, a sentence like: miPropiedad = MyTextField.textīut if you try to execute these examples just as they are, you will get errors from the Compiler. ‘Get’ is automatically invoked (and showed by the Debugger) every time we write for instance: Dim textVar As String = myProperty For example, every time we create one of these properties via Insert > Computed Property, we will define the property name, type and scope as we would do in the case of a regular property and when we refer to these kind of properties from our code, we will use the usual dot notation and, at the same time, we will assign new values using the habitual equal symbol (“=”).Īs you can see in the screenshot, below the property name we find both methods: Get and Set.

They aren’t! But they make our life as developers much easier compared with regular Properties.Īs developers, the computed properties definitions don’t differ a lot from regular ones. Nevertheless, let’s make clear that Xojo Computed Properties are not methods. The Object-Oriented Programming (OOP) concept found behind this feature is Method Overloading. So, in other programming languages, the first of these dedicated methods (or functions), the Setter, is the one invoked every time we want to modify the value of the associated property, while the Getter method is the one used from our code to retrieve the associated value. Some years ago, Xojo introduced the ability to use Computed Properties, something that is present in other programming languages too and is based on the use of dedicated methods to assign and retrieve the property value itself.