2. Adding a Button to the Screen

In this quick tutorial we shall see how to add a set of push buttons to the screen.

The SDK comes this standard classes for screen drawing and listening for touch input. One of these classes are ButtonView. ButtonView display a simple push button and accepts touch input.

Reacting to clicks

Let us go create a new Mono project, fire up your terminal and:

$ monomake project buttonExample

To create a button on the screen we first add a ButtonView object to AppController. Insert this into app_controller.h:

class AppController : public mono::IApplication {
    // This is the text label object that will displayed
    TextLabelView helloLabel;

    // We add this: our button object
    ButtonView btn;

    // The default constructor

    // We also add this callback function for button clicks
    void buttonClick();

We added a member object for the button itself and a member method for its callback. This callback is a function that is called, then the button is clicked.

Now, in the implementation file (app_controller.cpp), we add the button the contructor initializer list:

AppController::AppController() :

    // Call the TextLabel's constructor, with a Rect and a static text
    helloLabel(Rect(0,100,176,20), "Hi, I'm Mono!"),

    // Here we initialize the button
    btn(Rect(20, 175, 136, 40), "Click me!")

The button’s constructor takes 2 arguments: position and dimension rectangle and its text label. The first argument is a Rect object, it defines the rectangle where the Button lives. This means it will draw itself in the rectangle and listen for touch input in this rectangle:

The position and dimension of the button

The second argument is the text label that is displayed inside the button. In this example it is just the text Click me!

To trigger a response when we click the button, we need to implement the function body for the buttonClick method. In app_controller.cpp add this method:

void AppController::buttonClick()
    helloLabel.setText("Button clicked!");

This method changes the content of the project templates existing helloLabel to a new text. Lastly, we connect the button click handler to call our function. From inside the monoWakeFromReset method, we append:

// tell the label to show itself on the screen

// set the callback for the button click handler
btn.setClickCallback<AppController>(this, &AppController::buttonClick);
// set the button to be shown

That’s it! Run make install and see the example run on Mono:

Before and after the button is clicked