Getting ready

In this recipe, we will use the Kv language for the design of the widgets, so you will need to be familiar with the language or have completed the previous chapter. Also, this recipe will use the common Button widget for reference.

How to do it…

Follow the steps in this recipe:

How it works…

Let's start with the KV file. The first line is the name of the rule, similar to the class name in the Python file. The second line is the definition of the button widget, and the third line is the ID of the button, which is necessary to do the call of the widget inside the Python code, and the fourth line is the definition of the text in the button.

With regard to the Python code, the initial four lines are usual to use Kivy and the button widget. Note the following fifth line:

class MyW(Widget):

This is where we define the class associated with our rule in the KV file. Now consider the sixth line:

def on_touch_down(self, touch):

Here, we start the declaration of the dispatched on_touch_down method; you must note the parameter touch in the declaration, and this parameter is necessary to call the event using the input—in this case—the mouse. Next, the seventh line is:

 if 'button' in touch.profile:

This is a verification line, because we need to be sure that the input device used in the platform, where we are running our code, supports the button profile. If this line is not present when the next line is performed, the app could crash. Finally, the eighth line:

 self.ids.button1.text = touch.button

This line is where we do the call to the button profile, which gives the information on which mouse button is touched by the user (the right one, left one, scroll up, and so on). Using this information, we change the text in our button that has ID button1. The last lines of the Python code are usual to run and display our Kivy interface. Just remember that the initial part of the name of the classis as follows:

class e1App(App):

Note that it will be the same as the KV file, so the name of the KV file in this case is e1.kv.

A last thing to remark is that we do not limit the input event to the button, so the touch can occur anywhere within the window.

There's more…

Another interesting profile that we could call for the mouse is the pos attribute, which provides us with the position vector of the click in the window. Let's change the seventh line of the Python code to:

 self.ids.button1.text = str(touch.pos)

When we are calling the pos profile and changing the text in the button widget to the position where the click is performed, the str() built-in object is important because the touch.pos return is a vector. This means that we need to convert to a string to avoid compatibility issues.

See also

If you want to run your interface, take a look at our recipe Running your code. To get further details about widgets, see the recipes in Chapter 4, Widgets.