Add Trigger.onChange (#69)

Author: spacey-sooty

Diff for: commands2/button/trigger.py

@@ -122,6 +122,27 @@ def _():
 
         return self
 
+    def onChange(self, command: Command) -> Self:
+        """
+        Starts the command when the condition changes.
+
+        :param command: the command t start
+        :returns: this trigger, so calls can be chained
+        """
+
+        state = SimpleNamespace(pressed_last=self._condition())
+
+        @self._loop.bind
+        def _():
+            pressed = self._condition()
+
+            if state.pressed_last != pressed:
+                command.schedule()
+
+            state.pressed_last = pressed
+
+        return self
+
     def whileTrue(self, command: Command) -> Self:
         """
         Starts the given command when the condition changes to `True` and cancels it when the condition

Diff for: tests/test_trigger.py

@@ -42,6 +42,23 @@ def test_onFalse(scheduler: commands2.CommandScheduler):
     assert not command1.isScheduled()
 
 
+def test_onChange(scheduler: commands2.CommandScheduler):
+    finished = OOBoolean(False)
+    command1 = commands2.WaitUntilCommand(finished)
+
+    button = InternalButton()
+    button.setPressed(True)
+    button.onChange(command1)
+    scheduler.run()
+    assert not command1.isScheduled()
+    button.setPressed(False)
+    scheduler.run()
+    assert command1.isScheduled()
+    finished.set(True)
+    scheduler.run()
+    assert not command1.isScheduled()
+
+
 def test_whileTrueRepeatedly(scheduler: commands2.CommandScheduler):
     inits = OOInteger(0)
     counter = OOInteger(0)