Getting ready

In this recipe, we will use the Kv language for the design of the widgets, so we assume that the reader is familiar with the Kv language. Also, this recipe will use the common button and label widgets for reference.

How to do it…

Follow these steps:

How it works…

In the KV file, the first line as usual is the name of the rule. The second line is the definition of the button widget, the third line is the ID of the button, which is necessary to do the call of the widget inside the Python code, the fourth line specifies the initial position of the button, and the fifth line is the definition of the text in the button. The sixth line is the definition of the label widget, the seventh line is ID of the label, the eighth line is the initial position of the label, and the ninth line is the initial text of the label.

In relation to the Python code, the initial four lines are the usual lines to use Kivy and the button widget. Next, the fifth one:

from kivy.input.shape import ShapeRect

In this line, we import the information of ShapeRect to be compared with the touch performed in the app. The sixth line is:

class MyW(Widget):

This is where we define the class associated with our rule in the KV file. The seventh line:

 def on_touch_move(self, touch):

Here, we start the declaration of the dispatched on_touch_move method; you must note the parameter touch in the declaration, and this parameter is necessary to call the event by the input. The eighth and ninth lines are:

 if 'pos' in touch.profile:
 self.ids.button1.pos = touch.pos

Those lines change the position of the button. The tenth line is:

 if isinstance(touch.shape, ShapeRect):

It is where the comparison between the imported shape and the shape of the touch is performed. The eleventh line will change the label text with the dimension of the touch if this is rectangular. The last lines of the Python code are the usual lines to run and display our Kivy interface. Just remember that the initial part of the name of the class is:

class e6App(App):

It will be the same of the KV file; the name of the KV file in this case is e6.kv

See also

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