make sure SetView is called only once, otherwise fail fast

core/bandmap/bandmap.go

@@ -156,8 +156,10 @@ func (m *Bandmap) Close() {
 
 func (m *Bandmap) SetView(view View) {
 	if view == nil {
-		m.view = new(nullView)
-		return
+		panic("bandmap.Bandmap.SetView must not be called with nil")
+	}
+	if _, ok := m.view.(*nullView); !ok {
+		panic("bandmap.Bandmap.SetView was already called")
 	}
 
 	m.view = view

core/callinfo/callinfo.go

@@ -102,9 +102,12 @@ type View interface {
 
 func (c *Callinfo) SetView(view View) {
 	if view == nil {
-		c.view = new(nullView)
-		return
+		panic("callinfo.Callinfo.SetView must not be called with nil")
+	}
+	if _, ok := c.view.(*nullView); !ok {
+		panic("callinfo.Callinfo.SetView was already called")
 	}
+
 	c.view = view
 	c.view.SetPredictedExchangeFields(c.theirExchangeFields)
 }

core/entry/entry.go

@@ -165,9 +165,12 @@ func (c *Controller) emitCallsignLogged(callsign string, frequency core.Frequenc
 
 func (c *Controller) SetView(view View) {
 	if view == nil {
-		c.view = &nullView{}
-		return
+		panic("entry.Controller.SetView must not be called with nil")
+	}
+	if _, ok := c.view.(*nullView); !ok {
+		panic("entry.Controller.SetView was already called")
 	}
+
 	c.view = view
 	c.Clear()
 	c.refreshUTC()
@@ -301,10 +304,6 @@ func (c *Controller) StartAutoRefresh() {
 
 func (c *Controller) refreshUTC() {
 	c.asyncRunner(func() {
-		if c.view == nil {
-			return
-		}
-
 		utc := c.clock.Now().UTC()
 		c.view.SetUTC(utc.Format("15:04"))
 	})

core/newcontest/newcontest.go

@@ -42,9 +42,12 @@ type Controller struct {
 
 func (c *Controller) SetView(view View) {
 	if view == nil {
-		c.view = new(nullview)
-		return
+		panic("newcontest.Controller.SetView must not be called with nil")
 	}
+	if c.view != nil {
+		panic("newcontest.Controller.SetView was already called")
+	}
+
 	c.view = view
 }
 

core/parrot/parrot.go

@@ -73,10 +73,15 @@ func (p *Parrot) Notify(listener any) {
 }
 
 func (p *Parrot) SetView(view View) {
-	p.view = view
-	if view != nil {
-		view.SetParrotActive(p.active)
+	if view == nil {
+		panic("parrot.Parrot.SetView must not be called with nil")
+	}
+	if p.view != nil {
+		panic("parrot.Parrot.SetView was already called")
 	}
+
+	p.view = view
+	view.SetParrotActive(p.active)
 }
 
 func (p *Parrot) SetInterval(interval time.Duration) {

core/rate/rate.go

@@ -69,9 +69,12 @@ func (c *Counter) StartAutoRefresh() {
 
 func (c *Counter) SetView(view View) {
 	if view == nil {
-		c.view = new(nullView)
-		return
+		panic("rate.Counter.SetView must not be called with nil")
+	}
+	if _, ok := c.view.(*nullView); !ok {
+		panic("rate.Counter.SetView was already called")
 	}
+
 	c.view = view
 	c.view.SetGoals(c.qsosGoal, c.pointsGoal, c.multisGoal)
 	c.view.ShowRate(c.QSORate)

core/score/score.go

@@ -97,9 +97,12 @@ func (c *Counter) Result() int {
 
 func (c *Counter) SetView(view View) {
 	if view == nil {
-		c.view = new(nullView)
-		return
+		panic("score.Counter.SetView must not be called with nil")
+	}
+	if _, ok := c.view.(*nullView); !ok {
+		panic("score.Counter.SetView was already called")
 	}
+
 	c.view = view
 	c.view.SetGoals(c.contestPointsGoal, c.contestMultisGoal)
 	c.view.ShowScore(c.readScore) // READ

core/settings/settings.go

@@ -162,9 +162,12 @@ func (s *Settings) SetWriter(writer Writer) {
 
 func (s *Settings) SetView(view View) {
 	if view == nil {
-		s.view = new(nullView)
-		return
+		panic("settings.Settings.SetView must not be called with nil")
+	}
+	if _, ok := s.view.(*nullView); !ok {
+		panic("settings.Settings.SetView was already called")
 	}
+
 	s.view = view
 	s.showSettings()
 }