all: [API] deliver events one at a time to allow fine-grained event processing

Processing one event at a time allows a widget to execute commands after
the event that triggered it, instead of after all matching events.

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

widget/button.go

@@ -163,7 +163,11 @@ func (b *Clickable) Update(gtx layout.Context) []Click {
 	if b.focused {
 		filters = append(filters, key.Filter{Name: key.NameReturn}, key.Filter{Name: key.NameSpace})
 	}
-	for _, e := range gtx.Events(&b.keyTag, filters...) {
+	for {
+		e, ok := gtx.Event(&b.keyTag, filters...)
+		if !ok {
+			break
+		}
 		switch e := e.(type) {
 		case key.FocusEvent:
 			b.focused = e.Focus

widget/dnd.go

@@ -65,8 +65,12 @@ func (d *Draggable) Update(gtx layout.Context) (mime string, requested bool) {
 	}
 	d.pos = pos
 
-	for _, ev := range gtx.Events(&d.handle, transfer.SourceFilter{Type: d.Type}) {
-		if e, ok := ev.(transfer.RequestEvent); ok {
+	for {
+		e, ok := gtx.Event(&d.handle, transfer.SourceFilter{Type: d.Type})
+		if !ok {
+			break
+		}
+		if e, ok := e.(transfer.RequestEvent); ok {
 			return e.Type, true
 		}
 	}

widget/dnd_test.go

@@ -34,7 +34,7 @@ func TestDraggable(t *testing.T) {
 	stack.Pop()
 
 	drag.Update(gtx)
-	r.Events(drag, transfer.TargetFilter{Type: drag.Type})
+	r.Event(drag, transfer.TargetFilter{Type: drag.Type})
 	r.Frame(gtx.Ops)
 	r.Queue(
 		pointer.Event{
@@ -52,21 +52,27 @@ func TestDraggable(t *testing.T) {
 	)
 	ofr := &offer{data: "hello"}
 	drag.Update(gtx)
-	r.Events(drag, transfer.TargetFilter{Type: drag.Type})
+	r.Event(drag, transfer.TargetFilter{Type: drag.Type})
 	drag.Offer(gtx, "file", ofr)
-	r.Frame(gtx.Ops)
 
-	evs := r.Events(drag, transfer.TargetFilter{Type: drag.Type})
-	if len(evs) != 2 {
-		t.Fatalf("expected 3 event, got %d", len(evs))
+	e, ok := r.Event(drag, transfer.TargetFilter{Type: drag.Type})
+	if !ok {
+		t.Fatalf("expected event")
 	}
-	ev := evs[0].(transfer.DataEvent)
+	ev := e.(transfer.DataEvent)
 	if got, want := ev.Type, "file"; got != want {
 		t.Errorf("expected %v; got %v", got, want)
 	}
 	if ofr.closed {
 		t.Error("offer closed prematurely")
 	}
+	e, ok = r.Event(drag, transfer.TargetFilter{Type: drag.Type})
+	if !ok {
+		t.Fatalf("expected event")
+	}
+	if _, ok := e.(transfer.CancelEvent); !ok {
+		t.Fatalf("expected transfer.CancelEvent event")
+	}
 	r.Frame(gtx.Ops)
 	if !ofr.closed {
 		t.Error("offer was not closed")

widget/editor.go

@@ -380,7 +380,11 @@ func (e *Editor) processKey(gtx layout.Context) {
 	}
 	// adjust keeps track of runes dropped because of MaxLen.
 	var adjust int
-	for _, ke := range gtx.Events(&e.eventKey, filters...) {
+	for {
+		ke, ok := gtx.Event(&e.eventKey, filters...)
+		if !ok {
+			break
+		}
 		e.blinkStart = gtx.Now
 		switch ke := ke.(type) {
 		case key.FocusEvent:

widget/enum.go

@@ -66,7 +66,11 @@ func (e *Enum) Update(gtx layout.Context) bool {
 		if e.focused && e.focus == state.key {
 			filters = append(filters, key.Filter{Name: key.NameReturn}, key.Filter{Name: key.NameSpace})
 		}
-		for _, ev := range gtx.Events(&state.tag, filters...) {
+		for {
+			ev, ok := gtx.Event(&state.tag, filters...)
+			if !ok {
+				break
+			}
 			switch ev := ev.(type) {
 			case key.FocusEvent:
 				if ev.Focus {

widget/example_test.go

@@ -109,7 +109,11 @@ func ExampleDraggable_Layout() {
 		ds.Pop()
 
 		// Check for the received data.
-		for _, ev := range gtx.Events(&drop, transfer.TargetFilter{Type: mime}) {
+		for {
+			ev, ok := gtx.Event(&drop, transfer.TargetFilter{Type: mime})
+			if !ok {
+				break
+			}
 			switch e := ev.(type) {
 			case transfer.DataEvent:
 				data := e.Open()

widget/selectable.go

@@ -319,7 +319,11 @@ func (e *Selectable) processKey(gtx layout.Context) {
 			key.Filter{Name: "A", Required: key.ModShortcut},
 		)
 	}
-	for _, ke := range gtx.Events(e, filters...) {
+	for {
+		ke, ok := gtx.Event(e, filters...)
+		if !ok {
+			break
+		}
 		switch ke := ke.(type) {
 		case key.FocusEvent:
 			e.focused = ke.Focus