In our last article on CodenameOne I discussed basic usage of its Designer tool. In this article we will look at The tool and it’s usage in more detail.
CodenameOne UI basics
Every UI element within CodenameOne is a subclass (directly or indirectly) of the Component class. If you are familiar with Android development, you can think of the
Component class as the View class. Every
Component has four style objects:
Each of these styles contains information about the UI, such as font, colors, border, etc.
By default, CodenameOne applications use the running platforms Native UI, but this can be changed. CodenameOne defines a constant called
includeNativeBool. When it is set to
true, the Native UI is used. Otherwise, you can create themes that will look the same in every platform, such as the Leather Theme.
Layout Managers deal with positioning UI elements in a view. Every layout manager has a base abstract class, Layout. Developers can create their own layout managers. Codename One comes with the following predefined layout managers:
- FlowLayout – Places components using their set size and line breaks. It’s simplistic and doesn’t always break lines properly. This is the default manager.
- BoxLayout X/Y – Places components in a column/row given the set size on the inverse axis and stretching them on the main axis. The X version doesn’t cause line breaks and aligns better than flow layout.
- GridLayout – Places components on an even grid where all the elements have an even size.
- TableLayout – Places components in a table with constraints row/column spanning etc.
- BorderLayout – Places components in one of 5 positions, one of the 4 borders or the center. Supports absolute center mode where the center component isn’t stretched.
You can learn more about the usage of layouts in this video.
Integrating the Design Tool with Java Code
Create a new CodenameOne project. I will call mine
FirstExample, I’m going to use the native theme and the Hello World (Visual) theme. After the project is created, open the Designer tool by double clicking the
theme.res file. You can change the view you see by choosing an item on the Native Theme menu. If using the iOS6 theme, the initial view would be this:
We are about to change this. To add other items, drag them from Core Components to the view. You can change the text of the components by double clicking them.
Now change the header (I’m setting it to “Hello CodenameOne”) and the “Hi World” label. Add a Text Field and a Button, finally making the view like this:
To change the layout (I would prefer the UI elements in the middle of the screen, one above the other), select the
Main[Form], and then search for
Layout on the
Properties tab. The layout is set to
FlowLayout, but we can change it by clicking it. Set the layout to
Box Layout Y:
Now you can see that the UI components are aligned vertically, on the Y axis.
Run this in the simulator (don’t forget to save first). You will notice that the button doesn’t work, since there is no code attached to it’s click event.
Connecting UI components with Java code
The Designer tool is helpful for adding event listeners to UI components. We will now use it to add an ActionEvent listener to the button.
Change the variable names for the field and the button. call the text field
nameField and the button
helloButton. To add a listener to the button, select the button, go to the Events tab and click Action Event. This will create a protected method called
onMain_HelloButtonAction(Component c, ActionEvent event) that will be executed every time the button is clicked.
We want to show a dialog when the button is clicked that says “Hello User”, but showing the user’s name instead of “User”. To accomplish this, add the below code inside the method created above:
TextField nameField = (TextField) findByName("nameField", c); String userName = nameField.getText(); String greet = "Hello, "+userName+"!"; Dialog.show("Greetings", greet, "OK", null);
findByName() method is the equivalent of
findViewById() in Android. It receives two arguments, the name of the UI component (defined using the Designer tool), and the
rootComponent, which is the container (the view).
I used Dialog.show() to make the dialog visible. The first argument is the
Dialog title, the second is the body, the third is the
okText and the last is the
cancelText (which I set to
Now when running the application in the simulator, you will see the below:
The Designer tool is a powerful part of the Codename One toolset. Have any of you used it for a project?
Aldo is a Code-Lover and a student of Computer Engineering from Albania. His short-term goal is that of becoming a full-stack developer, focusing on Android, Ruby technologies and DevOps techniques.