lib/app: intro back_button abstraction with navigation for multiple windows

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/app/ui.nit b/lib/app/ui.nit
index 4efbb87..5f99576 100644 (file)
--- a/lib/app/ui.nit
+++ b/lib/app/ui.nit
@@ -28,8 +28,32 @@ redef class App
 
        # The current `Window` of this activity
        #
-       # This attribute must be set by refinements of `App`.
-       var window: Window is writable
+       # This attribute is set by `push_window`.
+       var window: Window is noinit
+
+       # Make visible and push `window` on the top of `pop_window`
+       #
+       # This method must be called at least once within `App::on_create`.
+       # It can be called at any times while the app is active.
+       fun push_window(window: Window)
+       do
+               window_stack.add window
+               self.window = window
+       end
+
+       # Pop the current `window` from the stack and show the previous one
+       #
+       # Require: `window_stack.not_empty`
+       fun pop_window
+       do
+               assert window_stack.not_empty
+               window_stack.pop
+               window = window_stack.last
+               window.on_resume
+       end
+
+       # Stack of active windows
+       var window_stack = new Array[Window]
 
        redef fun on_create do window.on_create
 
@@ -141,6 +165,12 @@ end
 # A window, root of the `Control` tree
 class Window
        super CompositeControl
+
+       # Should the back button be shown and used to go back to a previous window?
+       fun enable_back_button: Bool do return app.window_stack.length > 1
+
+       # The back button has been pressed, usually to open the previous window
+       fun on_back_button do app.pop_window
 end
 
 # A viewable `Control`