app,io/key,io/system: [API] replace system.CommandEvent with key.Event

It's much simpler to map the Android back button to a key.Event and
let the usual key filtering determine whether to block its default
behaviour.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_android.go

@@ -571,9 +571,7 @@ func Java_org_gioui_GioView_onFrameCallback(env *C.JNIEnv, class C.jclass, view
 //export Java_org_gioui_GioView_onBack
 func Java_org_gioui_GioView_onBack(env *C.JNIEnv, class C.jclass, view C.jlong) C.jboolean {
 	w := cgo.Handle(view).Value().(*window)
-	ev := &system.CommandEvent{Type: system.CommandBack}
+	if w.callbacks.Event(key.Event{Name: key.NameBack}) {
-	w.callbacks.Event(ev)
-	if ev.Cancel {
 		return C.JNI_TRUE
 	}
 	return C.JNI_FALSE

app/os_js.go

@@ -172,12 +172,9 @@ func (w *window) addEventListeners() {
 		return nil
 	})
 	w.addEventListener(w.window, "popstate", func(this js.Value, args []js.Value) interface{} {
-		ev := &system.CommandEvent{Type: system.CommandBack}
+		if w.w.Event(key.Event{Name: key.NameBack}) {
-		w.w.Event(ev)
-		if ev.Cancel {
 			return w.browserHistory.Call("forward")
 		}
-
 		return w.browserHistory.Call("back")
 	})
 	w.addEventListener(w.document, "visibilitychange", func(this js.Value, args []js.Value) interface{} {

app/window.go

@@ -416,29 +416,31 @@ func (c *callbacks) SetDriver(d driver) {
 	c.w.wakeupFuncs <- wakeup
 }
 
-func (c *callbacks) Event(e event.Event) {
+func (c *callbacks) Event(e event.Event) bool {
 	if c.d == nil {
 		panic("event while no driver active")
 	}
 	c.waitEvents = append(c.waitEvents, e)
 	if c.busy {
-		return
+		return true
 	}
 	c.busy = true
 	defer func() {
 		c.busy = false
 	}()
+	var handled bool
 	for len(c.waitEvents) > 0 {
 		e := c.waitEvents[0]
 		copy(c.waitEvents, c.waitEvents[1:])
 		c.waitEvents = c.waitEvents[:len(c.waitEvents)-1]
-		c.w.processEvent(c.d, e)
+		handled = c.w.processEvent(c.d, e)
 	}
 	c.w.updateState(c.d)
 	if c.w.closing {
 		c.w.closing = false
 		c.d.Close()
 	}
+	return handled
 }
 
 // SemanticRoot returns the ID of the semantic root.
@@ -740,10 +742,10 @@ func (w *Window) updateState(d driver) {
 	}
 }
 
-func (w *Window) processEvent(d driver, e event.Event) {
+func (w *Window) processEvent(d driver, e event.Event) bool {
 	select {
 	case <-w.dead:
-		return
+		return false
 	default:
 	}
 	switch e2 := e.(type) {
@@ -816,9 +818,6 @@ func (w *Window) processEvent(d driver, e event.Event) {
 		}
 		w.processFrame(d, frameStart)
 		w.updateCursor(d)
-	case *system.CommandEvent:
-		w.out <- e
-		w.waitAck(d)
 	case system.DestroyEvent:
 		w.destroyGPU()
 		w.out <- e2
@@ -838,10 +837,12 @@ func (w *Window) processEvent(d driver, e event.Event) {
 		e2.Config.Size = e2.Config.Size.Sub(w.decorations.size)
 		w.out <- e2
 	case event.Event:
-		if w.queue.q.Queue(e2) {
+		handled := w.queue.q.Queue(e2)
+		if handled {
 			w.setNextFrame(time.Time{})
 			w.updateAnimation(d)
 		} else if e, ok := e.(key.Event); ok && e.State == key.Press {
+			handled = true
 			switch {
 			case e.Name == key.NameTab && e.Modifiers == 0:
 				w.moveFocus(router.FocusForward, d)
@@ -855,10 +856,14 @@ func (w *Window) processEvent(d driver, e event.Event) {
 				w.moveFocus(router.FocusLeft, d)
 			case e.Name == key.NameRight && e.Modifiers == 0:
 				w.moveFocus(router.FocusRight, d)
+			default:
+				handled = false
 			}
 		}
 		w.updateCursor(d)
+		return handled
 	}
+	return true
 }
 
 func (w *Window) run(options []Option) {

io/key/key.go

@@ -223,6 +223,7 @@ const (
 	NameDown           = "Down"
 	NameLeft           = "Left"
 	NameRight          = "Right"
+	NameBack           = "Back"
 )
 
 // Contain reports whether m contains all modifiers

io/system/system.go

@@ -54,20 +54,9 @@ type StageEvent struct {
 	Stage Stage
 }
 
-// CommandEvent is a system event. Unlike most other events, CommandEvent is
-// delivered as a pointer to allow Cancel to suppress it.
-type CommandEvent struct {
-	Type CommandType
-	// Cancel suppress the default action of the command.
-	Cancel bool
-}
-
 // Stage of a Window.
 type Stage uint8
 
-// CommandType is the type of a CommandEvent.
-type CommandType uint8
-
 const (
 	// StagePaused is the Stage for inactive Windows.
 	// Inactive Windows don't receive FrameEvents.
@@ -76,12 +65,6 @@ const (
 	StageRunning
 )
 
-const (
-	// CommandBack is the command for a back action
-	// such as the Android back button.
-	CommandBack CommandType = iota
-)
-
 func (l Stage) String() string {
 	switch l {
 	case StagePaused:
@@ -93,7 +76,6 @@ func (l Stage) String() string {
 	}
 }
 
-func (FrameEvent) ImplementsEvent()    {}
+func (FrameEvent) ImplementsEvent()   {}
-func (StageEvent) ImplementsEvent()    {}
+func (StageEvent) ImplementsEvent()   {}
-func (*CommandEvent) ImplementsEvent() {}
+func (DestroyEvent) ImplementsEvent() {}
-func (DestroyEvent) ImplementsEvent()  {}