TabItem: add possibility to attach an EventHandler

fix #953

Author: gucio321

Widgets.go

@@ -612,10 +612,11 @@ func (d *DummyWidget) Build() {
 
 // TabItemWidget is an item in TabBarWidget.
 type TabItemWidget struct {
-	label  string
-	open   *bool
-	flags  TabItemFlags
-	layout Layout
+	label        string
+	open         *bool
+	flags        TabItemFlags
+	layout       Layout
+	eventHandler *EventHandler
 }
 
 // TabItem creates new TabItem.
@@ -648,6 +649,12 @@ func (t *TabItemWidget) Flags(flags TabItemFlags) *TabItemWidget {
 	return t
 }
 
+// EventHandler allows to attach a custym EventHandler to the tab item in order to detect events on it.
+func (t *TabItemWidget) EventHandler(handler *EventHandler) *TabItemWidget {
+	t.eventHandler = handler
+	return t
+}
+
 // Layout is a layout displayed when item is opened.
 func (t *TabItemWidget) Layout(widgets ...Widget) *TabItemWidget {
 	t.layout = Layout(widgets)
@@ -656,7 +663,13 @@ func (t *TabItemWidget) Layout(widgets ...Widget) *TabItemWidget {
 
 // BuildTabItem executes tab item build steps.
 func (t *TabItemWidget) BuildTabItem() {
-	if imgui.BeginTabItemV(t.label, t.open, imgui.TabItemFlags(t.flags)) {
+	start := imgui.BeginTabItemV(t.label, t.open, imgui.TabItemFlags(t.flags))
+
+	if t.eventHandler != nil {
+		t.eventHandler.Build()
+	}
+
+	if start {
 		t.layout.Build()
 		imgui.EndTabItem()
 	}

examples/widgets/widgets.go

@@ -161,7 +161,9 @@ func loop() {
 			g.TabItem("Multiline Input").Layout(
 				g.Label("This is first tab with a multiline input text field"),
 				g.InputTextMultiline(&multiline).Size(g.Auto, g.Auto),
-			),
+			).EventHandler(g.Event().OnClick(g.MouseButtonLeft, func() {
+				fmt.Println("MultipleInput tab clicked!")
+			})),
 			g.TabItem("Tree").Layout(
 				g.TreeNode("TreeNode1").Flags(g.TreeNodeFlagsCollapsingHeader|g.TreeNodeFlagsDefaultOpen).Layout(
 					g.Custom(func() {