Added callback functions for focus and blur events.

box.go

@@ -45,9 +45,15 @@ type Box struct {
 	// The alignment of the title.
 	titleAlign int
 
-	// Whether or not this box has focus.
+	// Whether or not this box has focus. This is typically ignored for
+	// container primitives (e.g. Flex, Grid, Pages), as they will delegate
+	// focus to their children.
 	hasFocus bool
 
+	// Optional callback functions invoked when the primitive receives or loses
+	// focus.
+	focus, blur func()
+
 	// An optional capture function which receives a key event and returns the
 	// event to be forwarded to the primitive's default input handler (nil if
 	// nothing should be forwarded).
@@ -398,13 +404,39 @@ func (b *Box) DrawForSubclass(screen tcell.Screen, p Primitive) {
 	}
 }
 
+// SetFocusFunc sets a callback function which is invoked when this primitive
+// receives focus. Container primitives such as Flex or Grid may not be notified
+// if one of their descendents receive focus directly.
+//
+// Set to nil to remove the callback function.
+func (b *Box) SetFocusFunc(callback func()) *Box {
+	b.focus = callback
+	return b
+}
+
+// SetBlurFunc sets a callback function which is invoked when this primitive
+// loses focus. This does not apply to container primitives such as Flex or
+// Grid.
+//
+// Set to nil to remove the callback function.
+func (b *Box) SetBlurFunc(callback func()) *Box {
+	b.blur = callback
+	return b
+}
+
 // Focus is called when this primitive receives focus.
 func (b *Box) Focus(delegate func(p Primitive)) {
 	b.hasFocus = true
+	if b.focus != nil {
+		b.focus()
+	}
 }
 
 // Blur is called when this primitive loses focus.
 func (b *Box) Blur() {
+	if b.blur != nil {
+		b.blur()
+	}
 	b.hasFocus = false
 }
 

dropdown.go

@@ -507,9 +507,10 @@ func (d *DropDown) closeList(setFocus func(Primitive)) {
 
 // Focus is called by the application when the primitive receives focus.
 func (d *DropDown) Focus(delegate func(p Primitive)) {
-	d.Box.Focus(delegate)
 	if d.open {
 		delegate(d.list)
+	} else {
+		d.Box.Focus(delegate)
 	}
 }
 
@@ -518,7 +519,7 @@ func (d *DropDown) HasFocus() bool {
 	if d.open {
 		return d.list.HasFocus()
 	}
-	return d.hasFocus
+	return d.Box.HasFocus()
 }
 
 // MouseHandler returns the mouse handler for this primitive.

flex.go

@@ -207,6 +207,7 @@ func (f *Flex) Focus(delegate func(p Primitive)) {
 			return
 		}
 	}
+	f.Box.Focus(delegate)
 }
 
 // HasFocus returns whether or not this primitive has focus.
@@ -216,7 +217,7 @@ func (f *Flex) HasFocus() bool {
 			return true
 		}
 	}
-	return false
+	return f.Box.HasFocus()
 }
 
 // MouseHandler returns the mouse handler for this primitive.

form.go

@@ -550,7 +550,7 @@ func (f *Form) Draw(screen tcell.Screen) {
 // Focus is called by the application when the primitive receives focus.
 func (f *Form) Focus(delegate func(p Primitive)) {
 	if len(f.items)+len(f.buttons) == 0 {
-		f.hasFocus = true
+		f.Box.Focus(delegate)
 		return
 	}
 	f.hasFocus = false
@@ -595,10 +595,10 @@ func (f *Form) Focus(delegate func(p Primitive)) {
 
 // HasFocus returns whether or not this primitive has focus.
 func (f *Form) HasFocus() bool {
-	if f.hasFocus {
+	if f.focusIndex() >= 0 {
 		return true
 	}
-	return f.focusIndex() >= 0
+	return f.Box.HasFocus()
 }
 
 // focusIndex returns the index of the currently focused item, counting form

frame.go

@@ -148,14 +148,14 @@ func (f *Frame) Focus(delegate func(p Primitive)) {
 	if f.primitive != nil {
 		delegate(f.primitive)
 	} else {
-		f.hasFocus = true
+		f.Box.Focus(delegate)
 	}
 }
 
 // HasFocus returns whether or not this primitive has focus.
 func (f *Frame) HasFocus() bool {
 	if f.primitive == nil {
-		return f.hasFocus
+		return f.Box.HasFocus()
 	}
 	return f.primitive.HasFocus()
 }

grid.go

@@ -250,7 +250,7 @@ func (g *Grid) Focus(delegate func(p Primitive)) {
 			return
 		}
 	}
-	g.hasFocus = true
+	g.Box.Focus(delegate)
 }
 
 // HasFocus returns whether or not this primitive has focus.
@@ -260,7 +260,7 @@ func (g *Grid) HasFocus() bool {
 			return true
 		}
 	}
-	return g.hasFocus
+	return g.Box.HasFocus()
 }
 
 // InputHandler returns the handler for this primitive.

pages.go

@@ -243,7 +243,7 @@ func (p *Pages) HasFocus() bool {
 			return true
 		}
 	}
-	return false
+	return p.Box.HasFocus()
 }
 
 // Focus is called by the application when the primitive receives focus.
@@ -260,6 +260,8 @@ func (p *Pages) Focus(delegate func(p Primitive)) {
 	}
 	if topItem != nil {
 		delegate(topItem)
+	} else {
+		p.Box.Focus(delegate)
 	}
 }
 

textview.go

@@ -648,7 +648,7 @@ func (t *TextView) Focus(delegate func(p Primitive)) {
 	// Implemented here with locking because this is used by layout primitives.
 	t.Lock()
 	defer t.Unlock()
-	t.hasFocus = true
+	t.Box.Focus(delegate)
 }
 
 // HasFocus returns whether or not this primitive has focus.
@@ -657,7 +657,7 @@ func (t *TextView) HasFocus() bool {
 	// callback.
 	t.Lock()
 	defer t.Unlock()
-	return t.hasFocus
+	return t.Box.HasFocus()
 }
 
 // Write lets us implement the io.Writer interface. Tab characters will be