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--- doc:appunti:prog:kivy [2019/02/25 11:11] – niccolo
+++ doc:appunti:prog:kivy [2023/10/06 11:04] – [Logging] niccolo
@@ Line 1: / Line 1: @@
 ====== Appunti Kivy ======
-**kivyexample.py**
+===== Python Code and KV Language =====
+This is the **kivyexample.py** file:
 <code python>
 #!/usr/bin/env python
 from kivy.app import App
 #kivy.require("1.8.0")
@@ Line 20: / Line 21: @@
     KivyExampleApp().run()
 </code>
+In the code above we derived a class named **KivyExampleApp** from the Kivy's **App** class. The Kivy code will automatically search for a file called **kivyexample.kv**, and it will parse it using the **KV language**. The name of the file is derived by the class name, making it all lowercase and removing the leftmost **//App//** part (if it exists). So this is the **kivyexample.kv** file:
 <file>
@@ Line 35: / Line 38: @@
         pos_hint: {'center_x': 0.5, 'center_y': 0.5}
     MyButton:
-        text: "Center right-top"
+        text: "Pos right-top"
         pos_hint: {'right': 0.9, 'top': 0.3}
     MyButton:
@@ Line 41: / Line 44: @@
         pos_hint: {'right': 0.5, 'top': 1.0}
 </file>
+In the Python code, the App constructor will return the **MyLayout** class, which is derived from the Kivy's **FloatLayout** class. The original class is an empty widget, but we added several buttons using the KV language.
+Notice that **MyLayout** is derived from **FloatLayout** declaring it into the **Python code**, whereas the **MyButton** class is derived from the original **Button** class using the KV language, via the //@Button// construct. The result should be something like this:
+{{.:kivy:kivyexample.png?direct&300|KivyExampleApp}}
+We used a KV file to define the graphic interface of our App, but **it is possible to do that using only Python code**, thus having only a single file. But doing as seen above has several advantages. First of all you can try to keep the **graphical presentation** and the **code logic** as much **separate** as possibile. Another advantage is that resizing the app's window, will resize all its contents automatically (if you are smart enough not to use absolute values); otherwise you have to bind the window-resize event to a function which should adjust each widget size and position.
+===== Using the Widget Class =====
+In general our App will return a class derived from the more generic **Widget** class, not the //FloatLayout// or others layouts classes. So the KV file will look like this:
+<file>
+<MyWidget>:
+    FloatLayout:
+        size: root.size
+        MyButton:
+            text: "Pos 0, 0"
+            pos_hint: {'x': 0, 'y': 0}
+</file>
+We requested that the FloatLayout expands to all the parent (root) **size**, so the example will give the same output as in the previous paragraph.
+===== A Real App With an ActionBar =====
+**kivywindowexample.py**
+<code python>
+#!/usr/bin/env python
+from kivy.app import App
+#kivy.require("1.8.0")
+from kivy.uix.widget import Widget
+class MyWidget(Widget):
+    pass
+class KivyWindowExampleApp(App):
+    def build(self):
+        return MyWidget()
+if __name__ == "__main__":
+    KivyWindowExampleApp().run()
+</code>
+**kivywindowexample.kv**
+<file>
+<MyButton@Button>:
+    font_size: 28
+    color: 0,1,0,1
+    size_hint: 0.3, 0.2
+<MyWidget>:
+    BoxLayout:
+        size: root.size
+        orientation: 'vertical'
+        ActionBar:
+            pos_hint: {'top': 1}
+            ActionView:
+                use_separator: True
+                ActionPrevious:
+                    title: "MyGame"
+                    with_previous: False
+                ActionOverflow:
+                    ActionButton:
+                        text: "Exit"
+                    ActionButton:
+                        text: "About"
+                ActionButton:
+                    text: "New Game"
+        FloatLayout:
+            MyButton:
+                text: "Pos 0, 0"
+                pos_hint: {'x': 0, 'y': 0}
+            MyButton:
+                text: "Center x-y"
+                pos_hint: {'center_x': 0.5, 'center_y': 0.5}
+            MyButton:
+                text: "Pos right-top"
+                pos_hint: {'right': 0.9, 'top': 0.3}
+            MyButton:
+                text: "Pos 0.5, 1.0"
+                pos_hint: {'right': 0.5, 'top': 1.0}
+</file>
+{{.:kivy:kivywindowexample.png?direct&320|Kivy ActionBar Example}}
+===== Logging =====
+Like a plain Python program, it is possible for a Kivy app to produce some logging using the Kivy logger. The output will go, by default, to a file created into the app home directory, into the **files/app/.kivy/logs/** directory.
+<code python>
+from kivy.logger import Logger, LOG_LEVELS
+# Set the loglevel. The Android log file will be create into
+# [app_home]/files/app/.kivy/logs/
+Logger.setLevel(LOG_LEVELS['debug'])
+Logger.info('Informative message')
+</code>
+Without root privileges it is not possibile for another Android app (e.g. a file browser) to access the log directory. The Kivy **app home** will be into the adopted SD card, under something like this:
+<code>
+/mnt/expand/[UUID]/user/0/[fully.qualified.app.name]
+</code>
+Every time that the Kivy environment is initializated, a new log file will be created; the filename will be something like **kivy_YY-MM-DD_N.txt**, where YY-MM-DD is the date and N is a progressive integer starting from zero.