window. add close button interceptor to react on the window closing b…

…efore anything is done (#1180)

Add SetCloseIntercept to be able to veto window close.
Be aware client code should call window.Close() if the action was desired.

Fixes #467

internal/driver/glfw/window.go

@@ -74,6 +74,7 @@ type window struct {
 	mouseLastClick     fyne.CanvasObject
 	mousePressed       fyne.CanvasObject
 	onClosed           func()
+	onCloseIntercepted func()
 
 	xpos, ypos    int
 	width, height int
@@ -292,6 +293,10 @@ func (w *window) SetOnClosed(closed func()) {
 	w.onClosed = closed
 }
 
+func (w *window) SetCloseIntercept(callback func()) {
+	w.onCloseIntercepted = callback
+}
+
 func (w *window) getMonitorForWindow() *glfw.Monitor {
 	xOff := w.xpos + (w.width / 2)
 	yOff := w.ypos + (w.height / 2)
@@ -404,7 +409,20 @@ func (w *window) Close() {
 	if w.viewport == nil {
 		return
 	}
-	w.closed(w.viewport)
+
+	w.viewport.SetShouldClose(true)
+
+	w.canvas.walkTrees(nil, func(node *renderCacheNode) {
+		switch co := node.obj.(type) {
+		case fyne.Widget:
+			cache.DestroyRenderer(co)
+		}
+	})
+
+	// trigger callbacks
+	if w.onClosed != nil {
+		w.queueEvent(w.onClosed)
+	}
 }
 
 func (w *window) ShowAndRun() {
@@ -446,19 +464,14 @@ func (w *window) Canvas() fyne.Canvas {
 }
 
 func (w *window) closed(viewport *glfw.Window) {
-	viewport.SetShouldClose(true)
+	viewport.SetShouldClose(false)
 
-	w.canvas.walkTrees(nil, func(node *renderCacheNode) {
-		switch co := node.obj.(type) {
-		case fyne.Widget:
-			cache.DestroyRenderer(co)
-		}
-	})
-
-	// trigger callbacks
-	if w.onClosed != nil {
-		w.queueEvent(w.onClosed)
+	if w.onCloseIntercepted != nil {
+		w.queueEvent(w.onCloseIntercepted)
+		return
 	}
+
+	w.Close()
 }
 
 // destroy this window and, if it's the last window quit the app

internal/driver/glfw/window_test.go

@@ -821,6 +821,38 @@ func TestWindow_Clipboard(t *testing.T) {
 	cb.SetContent(cliboardContent)
 }
 
+func TestWindow_CloseInterception(t *testing.T) {
+	d := NewGLDriver()
+	w := d.CreateWindow("test").(*window)
+	w.create()
+
+	onIntercepted := false
+	onClosed := false
+	w.SetCloseIntercept(func() {
+		onIntercepted = true
+	})
+	w.SetOnClosed(func() {
+		onClosed = true
+	})
+	w.Close()
+	w.waitForEvents()
+	assert.False(t, onIntercepted) // The interceptor is not called by the Close.
+	assert.True(t, onClosed)
+
+	onIntercepted = false
+	onClosed = false
+	w.closed(w.viewport)
+	w.waitForEvents()
+	assert.True(t, onIntercepted) // The interceptor is called by the closed.
+	assert.False(t, onClosed)     // If the interceptor is set Close is not called.
+
+	onClosed = false
+	w.SetCloseIntercept(nil)
+	w.closed(w.viewport)
+	w.waitForEvents()
+	assert.True(t, onClosed) // Close is called if the interceptor is not set.
+}
+
 // This test makes our developer screens flash, let's not run it regularly...
 //func TestWindow_Shortcut(t *testing.T) {
 //	w := createWindow("Test")

internal/driver/gomobile/window.go

@@ -9,10 +9,11 @@ import (
 )
 
 type window struct {
-	title    string
-	visible  bool
-	onClosed func()
-	isChild  bool
+	title              string
+	visible            bool
+	onClosed           func()
+	onCloseIntercepted func()
+	isChild            bool
 
 	clipboard fyne.Clipboard
 	canvas    *mobileCanvas
@@ -92,6 +93,10 @@ func (w *window) SetOnClosed(callback func()) {
 	w.onClosed = callback
 }
 
+func (w *window) SetCloseIntercept(callback func()) {
+	w.onCloseIntercepted = callback
+}
+
 func (w *window) Show() {
 	menu := fyne.CurrentApp().Driver().(*mobileDriver).findMenu(w)
 	menuButton := widget.NewButtonWithIcon("", theme.MenuIcon(), func() {
@@ -103,7 +108,7 @@ func (w *window) Show() {
 
 	if w.isChild {
 		exit := widget.NewButtonWithIcon("", theme.CancelIcon(), func() {
-			w.Close()
+			w.tryClose()
 		})
 		title := widget.NewLabel(w.title)
 		title.Alignment = fyne.TextAlignCenter
@@ -129,6 +134,15 @@ func (w *window) Hide() {
 	}
 }
 
+func (w *window) tryClose() {
+	if w.onCloseIntercepted != nil {
+		w.onCloseIntercepted()
+		return
+	}
+
+	w.Close()
+}
+
 func (w *window) Close() {
 	d := fyne.CurrentApp().Driver().(*mobileDriver)
 	pos := -1

test/testwindow.go

@@ -5,11 +5,12 @@ import (
 )
 
 type testWindow struct {
-	title      string
-	fullScreen bool
-	fixedSize  bool
-	focused    bool
-	onClosed   func()
+	title              string
+	fullScreen         bool
+	fixedSize          bool
+	focused            bool
+	onClosed           func()
+	onCloseIntercepted func()
 
 	canvas    *testCanvas
 	clipboard fyne.Clipboard
@@ -112,6 +113,10 @@ func (w *testWindow) SetOnClosed(closed func()) {
 	w.onClosed = closed
 }
 
+func (w *testWindow) SetCloseIntercept(callback func()) {
+	w.onCloseIntercepted = callback
+}
+
 func (w *testWindow) SetPadded(padded bool) {
 	w.canvas.SetPadded(padded)
 }

window.go

@@ -64,6 +64,10 @@ type Window interface {
 	// SetOnClosed sets a function that runs when the window is closed.
 	SetOnClosed(func())
 
+	// SetCloseIntercept sets a function that runs instead of closing if defined.
+	// Close() should be called explicitly in the interceptor to close the window.
+	SetCloseIntercept(func())
+
 	// Show the window on screen.
 	Show()
 	// Hide the window from the user.